Monthly Archives: February 2014

Electronics

Day 1 with the 4D Systems Intelligent LCD: Fail.

First off, I can point fingers, you can point fingers, who cares.. the fact is I’m pretty underwhelmed by my first day with the “Intelligent LCD”. I purchased the 4D Systems uLCD-43PCT LCD based on a SparkFun YouTube video describing how to use the product and associated software.This product is “intelligent” because it has it’s own processor and serial interface. The idea is to build the interface in software on your PC, drop it on a flash card and program the display.. then just use some simple serial commands to update the display, offloading all that work so I can add this to simple PIC projects with ease. By the p/n you can tell I got the 4.3″ LCD with capacitive touch screen.

I ordered the LCD second day air from Mouser ( @MouserElec ) because they offered the best price I could find. ($190+20) On the YouTube product review, Nick at SparkFun mentioned that he was using the 4D Systems USB to serial adapter because Spark Fun’s doesn’t work and can damage it (due to wiring?). I checked the specs and it says the LCD is 5V tolerant. I used my USB to serial adapter (TTL serial) which works great with PICs as long as they’re 5V tolerant. Well unfortunately, no luck… I can tell the LCD is communicating in some fashion because with a terminal client and with the terminal client built into the “Workbench” software (wasn’t that the name of the Amiga OS?).. in both programs I could enter carriage breaks or other characters and get some serial response from the LCD (usually NULLs (0x00).).. so there is some communication going on.. but the Workbench software itself declares the LCD is not attached. I also confirmed some communication with my logic analyzer. I ordered the 4D systems USB converter from Sparkfun and now I’m back to waiting. How lame.. if you really-really need a specific adapter why not just include it? what is the BOM on something like that? $1-2

I guess I’ll find out in a couple days when my Spark Fun order comes in. I was really hoping to get my display loaded. I spend a few hours on Sunday and Monday tweaking my design… TBC.

01ac1faae7f7a345fcea704ccb59b096fffb9fc41e 019f6ccc9d33cd592d6fa150307fb3f9bed275f037 0129ce0b8710388f61d5c50c95fcf4ec4ab9e0d820

Electronics

Experiment: TCN75A Temp sensor investigation

I covered the TCN75A i2C sensor a few weeks ago in a simple test to practice using I2C. I had never used I2C before and I knew it was time to stop avoiding it and jump in if I was going to use some of the fun chips and modules. Shortly after posting my results and code I jumped into @tymkrs IRC (visit their site if you’re curious) and Victor ( @vicatcu ) must have at least caught the article subject as he asked me if I noticed the chip runs a little warm (I think he mentioned roughly a deg C?). I had also noticed that oddity myself but I ignored it as I was only concerned with the actual communication. Victorย  ( @vicatcu ) posed the question: what would happen if I had a vented circuit board? Would that cure the chip from running hot?

Well that was half-brilliant wasn’t it? I had to know! Does under chip venting on the PCB effect temperature readings? I decided to purchase more sensors and SOIC break out boards as well as make sure my Fluke 51 was calibrated.

Upon receiving the SOIC breakout boards I took one and carefully used a Dremel to mill out the package outline. I had started to design my own PCBย  but I abandoned that because I didn’t want to wait for fabrication. I mounted the new sensor on it’s vented PCB then plugged the sensors right next to each other on breadboard and put the temperature probe wedged between the boards. Obviously factors like mounting the sensor near power transistors or near your power supply are always going to have some effect on your readings, and in some cases maybe that’s what your application is meant for. I wanted to take those factors out of the equation. My workshop heating and A/C was off for over a day when I did this test… no windows where open and the chips had been prepped for about 1/2 hour on the board while I wrote the code to test them out. I decided to read data straight from the I2C bus with some confirmation on RS-232 telemetry. I did this in case I introduced any math problem in my conversion in code. I also stuck with Celsius over Fahrenheit because that was the native output of the sensor.

SOIC breakout board with vent cut into it
SOIC breakout board with vent cut into it
The setup of the initial test.
The setup of the initial test.

After downloading code and checking everything out my Fluke 51 read 25.8 deg C, the un-vented TCN75A read 26.06 deg C and the vented TCN75A read 25.81 deg C. Over time the un-vented sensor would measure up to 0.400 deg C away from the other two. It’s not 1 deg C but it is something.

The TCN75A boards are back to back with the K type probe between them. To the bottom right you see the I2C pull up resistors with the logic analyzer tied to them. The PIC16F1509 is just to the right.

Temp sensor telemetry
Temp sensor telemetry; don’t mind the calculator. I was confirming a hexadecimal I2C address.

Test #2, a muffin fan…. same set up. No real change; roughly the same results.

Test #3! What about a change in temperature? I grabbed a cardboard box, put my test circuit and a bowl of ice with some water in the bottom of it, with a muffin fan blowing into the bowl and covered the whole thing in with saran wrap. Not the most insulated thing but I was only looking for a couple degrees. The test proved interesting… both sensors had some lag, and the venting only offered some minor help. It caught up first but they still have a fair amount of lag over the K type probe. In the graph provided I measured at even intervals over 15 minutes. The box settled out at the end (not enough insulation I imagine) the temperature flattened out so I dropped that data.

The Fluke 51 with K type thermocouple vs the normally mounted and modified mounting TCN75A temp sensors.
The Fluke 51 with K type thermocouple vs the normally mounted and modified mounting TCN75A temp sensors.

I can live with the results. I think if I were going to design a board where I wanted as close to an accurate temperature as I could get with this part I would definitely have a milled vent. In hind-sight I would make the vent so it is along the chip axis and protrudes past the edges of the chip. Thanks again to Victor for the great idea!

Tools and Test Equipment

Weller WD1001 and other updates

I’ll get the “other” updates out-of-the-way before talking about my new love! I’ve collected a solid number of PIC development boards over the last couple years and in about 3-4 weeks I’m going to do a review over what I have collected and what I’ve liked and disliked about them. Do you have any suggestions on a board I just can not miss? I am not sponsored, nor do I collect any money from blogging so I’m not going to buy dozens but I’d be willing to buy a few additional boards if someone has been holding off on pulling the trigger on a purchase. I’m not much of a “review” type person but I’m passionate about development boards for prototyping and I would hope my review would help give someone something to think about before purchasing something for their first or second project; PIC based or not. E-mail away!

It’s a changing of the guard on my bench. My beloved EC1002 is being replaced by the WD1001. It took me a while to decide on the WD1 platform. I decided on the WD1001 over the WD1002 strictly based on the pencil. The WMP appears to be more helpful for small circuit soldering. The WD1 base is very robust, it could be used as a weapon in a pinch. They cord to the pencil appears like it’s made from something that’s near impossible to tangle and is very flexible. The stand… a dream. The only thing it was missing out of the box was a connector to ground it. There is a base connector attachment which appears to be a 1/8″ mono tip/sleeve audio-type jack. I’ll just have to build something myself. Otherwise I’m in love with the purchase.

Weller WD1001 boxed

@whixr was really trying to sell me on the Hakko FX-888… he is in love with his. I did consider the purchase despite feeling like the blue/yellow made it difficult for me to take it seriously as a tool. They have a new silver version; Perhaps I’ll buy one to test out and send to my brother.ย I was also seriously considering Metcal.. but after a little I can tell I’ll have no regrets with the WD1002.

Old and New

Adam Fabio was definitely on team-Metcal and he just about had me sold. It all boiled down to a review of the WD1001 on YouTube and how agile that pencil is.

Check out how close you are to the work with that WMP handle! I really feel in control.

The handle and tip perfect for up-close small work!

 

Not the most exciting thing in the world, but a good iron really makes like easier. I put my time in with 25 and 35 watt wall corded pencils. The old radio shack models, even the 35W weller… nothing beats a nice thermostatically controlled station.

C DIY Electronics Microcontrollers PIC Robotics

Project Update: Spunk The Annoying Robot

The last robot I built was a Roomba Sumo Robot (Talos) for a small competition with co-workers. While collecting parts for this little eBay robot platform I got for somewhere in the neighborhood of 15$USD, I grabbed my Pololu motor controller and remember that I wrote that whole Sumo robot in ASM; that was a lot of code between two PICs.

The little robot I’m building now has very few specifications. It’s goal in life is to follow you around, but not too close. It should back away when needed and basically run around, pausing for a while in its search for someone to follow around. My wife named it Spunk because she’s certain to be the one it annoys most.

I’ve built the project as seen in the photo and written all primary code.. ordered a lot of battery management parts to see what I like the best. Determined I can’t get the robot to “find” people with the sensors I have, so I ordered more… so this little guy is half-done. I’ll shelve him until more parts arrive. I really only grabbed it down as it was 4 projects deep in the to-do list because I haven’t kept up with pre-ordering parts, or worse.. ordered the wrong things. I’m still on the hunt for a better display for the WX radio, ordered items for my RS-485 project, etc. etc..

The heart of Spunk is a PIC 18F14K22 on a TAUTIC 20 pin development board. Maybe Jayson ( @TAUTIC ) needs to pay me for all this advertising? ๐Ÿ˜‰ jk.. I just bought a couple of the boards because they fit my type of prototyping perfectly. This was my last one… time to make an order over at @tindie for some more.

Spunk getting probed.
Spunk getting probed.

For now, no code. I’ll post the old ASM code for the Pololu motor controller and the C code as well once it get it properly commented and make sure it at least mostly works. Once I do some real roving tests I’ll throw it on YouTube (and maybe the first tests of Talos as well)… TBC for now.

C Electronics PIC

Checkout: @tymkrs MIDI In Me + PIC18F14K22

I don’t want anyone thinking they’re going to see a bunch of music related items on the blog because I’m really no good at such things. My brother on the other hand is very talented and we recently decided he needed some more MIDI toys. A lot of his music is already created with the help of MIDI.

MIDI is “Musical Instrument Digital Interface“; a standard that defines hardware and protocol. If you want more information on it such as specifications Google is your friend.

My brother had some information on the specification but not really anything that helped me much. I did a lot of reading on the specifications on the MIDI Manufacturers Association webpage and then countless other sites describing the protocol in length. It even looks like there is a tutorial on the Arduino site, although I didn’t look at it because I don’t use them. Again, I’m not going to go into the protocol anymore than I discussed the specification. I’ll let you do that leg work. However, the *really* short version is there are a couple key commands followed (usually) by some extra bytes (generally 1 or 2). All the data is transmitted like normal 8N1 serial data at 31.25kbaud. Lucky for me 31.5k has a nice PIC SPBRG division value for low error rate (at 4MHz).

Hardware Interface: I decided I wasn’t going to build the 5mA loop interface and I remembered the Toymakers ( @tymkrs ) had a nice little interface board already built. One trip on over to their Tinde Store and I had it a few days later.

It’s a small kit, it came well packed, and it fit the bill just fine. I have nothing but praise this little kit with only one tiny little nit-picky mention. I wish they included a URL of the location of the instructions for building the kit. They had a couple resistors and I needed to know what was R1, R2, etc.. it was easy to find, a return trip to Tindie linked instructions, a construction video! and a lot of information on their website. So I know I’m picky.. If they wanted to make a 9.7 a 10.. that’d be it ๐Ÿ˜‰

The Toymakers Midi In Me Kit.
The Toymakers Midi In Me Kit.

After everything was plugged in, code was loaded on the PIC, a MIDI device plugged in.. etc.. I checked out the MIDI kit to see response and how noisy it might be… no complaints here.. it looked good…

MIDI In signal edge TEK0000

The Firmware: It’s just “sample” code. I haven’t written any real output yet because my brother is in charge of the “analog” bits which really means he is going to figure out what he wants in block diagrams and I will have to figure out how to make it happen in circuit. Right now I’m reading the MIDI signal in on UART by interrupt… and checking for my command signal. (I’m using a Control Change because of my MIDI device… you will most likely want to change this). The control change value is 0xB1 in my case, then… my device (Knob #1) which is 0x11 … and finally it gives me a value (knob position 0x00 to 0x7F). I’m taking that position value and transmitting it out the UART to my PC…

 

The output dropped onto my PC. Note: RealTerm allows me to enter in 31250 baud.. 8N1
The output dropped onto my PC. Note: RealTerm allows me to enter in 31250 baud.. 8N1
MIDI on the LA
MIDI on the LA

 

I used the TAUTIC 20 pin dev board (any groaning of “AGAIN??”??) … but a change-up! ๐Ÿ™‚ I used a PIC 18F14K22 … because I felt like getting crazy ๐Ÿ˜‰ and the 18 series is optimized for C so I will probably go back to the 18F series … I think the last time I used one was my ESR meter?  A few changes switching to the 18 series.. but nothing huge. Just getting used to slightly different registers.  Last warnings about the code; It’s simple… it’s just checking to see if your interface it working… (or if you’re sending MIDI and you don’t have a scope or LA). It has a lot of clutter because I was using it for some other non-MIDI related testing but it’s easy to spot and delete if you need to copy it as a starting point for whatever you’re working on. (Do share!)

/* 
 * File:   main.c
 * Author: Charles M Douvier
 * Contact at: http://iradan.com
 *
 * Created on February 8, 2014, 11:39 AM
 *
 * Target Device:
 * 18F14K22 on Tautic 20 pin dev board
 *
 * Project: MIDI Slave
 *
 *
 * Version:
 * 0.1  Configuration, 31.25Kbaud TX&RX
 * 0.2  Grab MIDI byte from 31.25K MIDI and turn around and TX the value of the
 *      MIDI command. <CMD: Control Change><Device><Value>
 *      <B1><11><value> //my example
 *
 */
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 4000000 //4Mhz FRC internal osc
#define __delay_us(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define __delay_ms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))
#endif

#include <xc.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

//config bits
#pragma config FOSC=IRC, WDTEN=OFF, PWRTEN=OFF, MCLRE=ON, CP0=OFF, CP1=OFF, BOREN=ON
#pragma config STVREN=ON, LVP=OFF, HFOFST=OFF, IESO=OFF, FCMEN=OFF

#define _XTAL_FREQ 4000000 //defined for delay

/*
 * Variables
 */

    long int    decm;           //long temp
    int     tempi;              //temp
    int     i, ilevel;                  //temp
    int     itxdata;            //int RS232 tx data
    char    buf[10];            //buff for iota
    volatile unsigned int uart_data;    // use 'volatile' qualifer as this is changed in ISR

/*
 *  Functions
 */

    void interrupt ISR() {

    if (PIR1bits.RCIF)          // see if interrupt caused by incoming data
    {
        uart_data = RCREG;     // read the incoming data
        PIR1bits.RCIF = 0;      // clear interrupt flag
                                //
    }

}

void uart_xmit(unsigned int mydata_byte) {

    while(!TXSTAbits.TRMT);    // make sure buffer full bit is high before transmitting
    TXREG = mydata_byte;       // transmit data
}

void serial_init(void)
{

    // calculate values of SPBRGL and SPBRGH based on the desired baud rate
    //
    // For 8 bit Async mode with BRGH=0: Desired Baud rate = Fosc/64([SPBRGH:SPBRGL]+1)
    // For 8 bit Async mode with BRGH=1: Desired Baud rate = Fosc/16([SPBRGH:SPBRGL]+1)

    TXSTAbits.BRGH=1;       // select low speed Baud Rate (see baud rate calcs below)
    TXSTAbits.TX9=0;        // select 8 data bits
    TXSTAbits.TXEN = 1;     // enable transmit

    RCSTAbits.SPEN=1;       // serial port is enabled
    RCSTAbits.RX9=0;        // select 8 data bits
    RCSTAbits.CREN=1;       // receive enabled

    //BRGH=1        31.25KHz
    //SPBRG=7

    SPBRG=7;               //

    PIR1bits.RCIF=0;        // make sure receive interrupt flag is clear
    PIE1bits.RCIE=1;        // enable UART Receive interrupt
    INTCONbits.PEIE = 1;    // Enable peripheral interrupt
    INTCONbits.GIE = 1;     // enable global interrupt

         __delay_ms(50);        // give time for voltage levels on board to settle

    //  uart_xmit('S');         // transmit a character example

}

void init_io(void) {
    TRISAbits.TRISA0 = 0; // output
    TRISAbits.TRISA1 = 0; // output
    TRISAbits.TRISA2 = 0; // output
    TRISAbits.TRISA4 = 0; // output
    TRISAbits.TRISA5 = 0; // output

    ANSEL = 0x00;         // no A/D
    ANSELH = 0x00;

    TRISBbits.TRISB4 = 0; // RB4 = nc
    TRISBbits.TRISB5 = 1; // RB5 = nc
    TRISBbits.TRISB6 = 0; // RB6 = nc
    TRISBbits.TRISB7 = 0; // RB7 = nc

    TRISCbits.TRISC0 = 0; // output
    TRISCbits.TRISC1 = 0; // output
    TRISCbits.TRISC2 = 0; // output
    TRISCbits.TRISC3 = 0; // output
    TRISCbits.TRISC4 = 0; // output
    TRISCbits.TRISC5 = 0; // output
    TRISCbits.TRISC6 = 1; // input
    TRISCbits.TRISC7 = 1; // input

}

void set_cmd11(void)
{
    //set an AD output
                while(uart_data==0x11)
            {
                i++; //wait for next char
            }
            ilevel = uart_data;         //finally the value
            uart_xmit(ilevel);
}

void check0xb1(void)
{
    if (uart_data == 0xB1)
    {
            while(uart_data==0xB1)
            {
                i++; //wait for next char
            }
            if ( uart_data == 0x11)     //and the knob 1 is "device 11"... 
               set_cmd11();
    }
}

int main(void) {

    init_io();

    // set up oscillator control register, using internal OSC at 4MHz.
    OSCCONbits.IRCF = 0x05; //set OSCCON IRCF bits to select OSC frequency 4MHz
    OSCCONbits.SCS = 0x02; //set the SCS bits to select internal oscillator block

    serial_init();

    decm=30;            //testing

    ltoa(buf,decm,10);  //long conversion to buffer
    tempi=strlen(buf);  //uh, adding leading zeros..
    uart_xmit('+');
    uart_xmit(itxdata);
    uart_xmit('.');
    LATAbits.LATA0=0;

    while (1) {

        i++;

        while (uart_data)
        {
            check0xb1();    //my midi device is sending a Control Change 0xB1
            uart_data=0;
        }

    }
    return (EXIT_SUCCESS);
}

 

Electronics

A note on conformal coating

In 1992 I was in high school going to a magnet school half-time for electronics. During the school year we had a regional electronics competition across the valley with all the school electronics programs in area. I don’t remember every bit of the competition; but as you can imagine there was theory, circuit analysis, math, troubleshooting and a practical soldering test. I somehow pulled off first place.. but not without having to pull off a soldering feat! Someone must have donated old through-hole aerospace related PCBs. There was a huge box of PCBs and they all had one ugly thing in common: Every single one had a thick layer of conformal coating! I’m guessing they came from Boeing. I was lucky; I’d run into these before or I’d likely not have won the competition. But I’ll get to that… Conformal coating comes in five (some claim six) types: Silicone, Epoxy, Acrylic, Polyurethane, and I’ll roll it up in “others”. They each have their application depending on your needs.. dielectric strength, flexibility, moisture resistance, etc. I typically use Silicone because it is flexible, and has good moisture resistance. The rest of this conversation is probably best viewed in video; so with that…

warning: this video drags on a little, 9 minutes could have easily been 4. I’m still not great at the whole video thing and I decided just to do this in one take.

Back to high-school days competition; the challenge was simple. Remove a two components and replace with new parts. I had gotten lucky that they had used acrylic coating and I chipped/scraped away most of the conformal coating without much damage or scaring. Everyone else just went and burnt through the coating to de-solder their targets… well as you can imagine it turned into a mess. Mine wasn’t anything I’d nail on a wall but apparently it was enough to be “award winning” ๐Ÿ™‚

C Electronics Microcontrollers PIC Programming Weather

Project: Si4707 Weather Radio

I purchased a Silicon Labs Si4707 weather band radio break out board (BOB) from Sparkfun a couple of months ago and finally did something with it. The Si4707 has a SAME ( Specific Area Message Encoding ) processor that allows alerting for only for a certain kinds of warnings. The weather band radio board receives from 162.40MHz to 162.55MHz; Its outputs is a 1/8″ jack with enough output to power a small speaker with low volume or earphones at a comfortable level of listening.

LCD Display of Si4707 Weather Band Radio Project
LCD Display of Si4707 Weather Band Radio Project

For my project I used MPLABX 2.0 with the XC8 C compiler. I decide to post this project before I was done programming because I’m about to customize this project for what I want. I thought it was a good time to make it available if a reader was interested in customizing the project without all the work of tearing apart what I had done. The code has all the right nuts and bolts and at most of the hard work done for you. All a person needs to do is a little(?) configuration to make the project meet your needs. You might consider going in another direction; volume up/down (programmable feauture!), tune up/down, and of course working with the SAME information, who knows?

Right now on the bench the PIC powers up, resets and powers up the radio, then tunes the radio via I2C to 162.55MHz. It finishes up by reading back the status and then dumps the Tuned Frequency and RSSI ( Received Signal Strength Indicator ) on to the LCD… then off to infinite loop land. In the next few days I plan on having my seven buttons for “quick tune” to the common frequencies (.40, 425, .45, etc..) and one additional monitor/standby switch. My radio will normally be silent and once it receives a weather alert it will un-mute the speaker and alert the LCD. The Standby/Monitor button will reset my alert.

I’ll throw my finished code up on github and you can download my version in a week or so [I’ll edit this and drop a link in when I’ve actually done this].

Another note of interest: the output of the audio amplifier is kind of weak. I recommend building another amplifier stage if you want the thing to wake you up in a weather emergency.

The attached code this is really rough around the edges.. I lot of hacking went into this and all of the unused functions are totally untested.

The Si4707 WX RX:

Okay, so $30.. not a bad price. And in the end I’m happy with the performance.

HOWEVER! The items I don’t like about it…

1. Sparkfun’s BOB threw pull up resistors on it.. that is annoying. I realize you can cut them out but .. how about some 2mm jumpers or something? I got burnt by them trying to get the I2C working. (RTFM!) ๐Ÿ™‚ I noticed lot of people seem to have issues with them being poorly sized according to the feedback I’ve read.

2. Wow it this thing pokey. I was a little confused by the application note for the product to determine worst case tune time, etc… basically I just ended up putting in 1000ms because 300ms was hit and miss for me. If I read it correctly worse case tune time for the AM radio version of the chip is 28 seconds!?

3. I2C! Well it worked fine but I suspect the board is a little noisy? with about 2 inches of wire leads I got enough ringing when the BOB wasn’t loaded by the logic analyzer for comm to fold. I ended up have to enable slew.  I also slowed the unit down to 25KHz from 100KHz because I have to wait for it anyways. It’ll probably work fine at 100KHz with slew on.

Top view of Si4707 Weather Band Radio Project. The power supply sits on the back of the LCD/keypad support board and the weather band sits sandwiched between the TAUTIC dev board and daughter-protoboard. The speaker was just thrown in there for quick testing.
Top view of Si4707 Weather Band Radio Project. The power supply sits on the back of the LCD/keypad support board and the weather band sits sandwiched between the TAUTIC dev board and daughter-protoboard. The speaker was just thrown in there for quick testing.

The circuit in general:

I haven’t included a schematic nor do I have any plans to. The photos show you I really am not using any support components besides LCD 10k pot you normally put on an LCD. I would have had pull up resistors but they were not required because of the BOB having them pre-installed.  You should be able to re-create the circuit just by looking at my TRISx/LATx initialization in the code. I commented it my version of adequate-enough… If you’re stumped, just ask!

5.0V input to run the LCD backlight and LCD main power (a standard 2 line 44780 compatible). The five volts also feeds the switching power supply to supply the PIC and 4707 with 3.3V power. I mistakenly thought the 4707 ran on 3.3V because I had been using an I2C product that was 3.3V only then had done a little switching around, oops… no harm, just a waste of the regulator. The 4707 runs 2.7-5.5V. My push button switches are designed to run in a 2×4 matrix. See the //notes in the code. Finally my PIC. I’m using (again!) the Microchip PIC 16F1509 microcontroller with a Tautic 20 pin development board and it’s daughter-board for a little prototyping space. I could maybe stretch this 20 PIN MCU a little more but I probably should have picked a slightly larger PIC for the IO. It’s enough for me though.

Side view. Note the whole project was just slapped on top of a piece of old PCB.. It's not even FR4.. just some old stuff. I made some "mounts" out of small copper strap and soldered the protoboard to the bare copper clad board.
Side view. Note the whole project was just slapped on top of a piece of old PCB.. It’s not even FR4.. just some old stuff. I made some “mounts” out of small copper strap and soldered the protoboard to the bare copper clad board.

So my final thoughts are I still have a lot of work and a lot of clean up work on this project. My temp mounting doesn’t have me totally won over. I also don’t like my “keypad” … I might by a pre-build “shield” and adapt it or maybe design my own PCB. I haven’t even hooked up the buttons because I haven’t decided if I’m happy-enough if the hardware.

The code:



/*
 * File:   newmain.c
 * Author: Charles M Douvier
 * Contact at: http://iradan.com
 *
 * Created on January 26, 2014, 12:00 PM
 *
 * Target Device:
 * 16F1509 on Tautic 20 pin dev board
 *
 * Project:
 *  I2C Testing with the TCN75A
 *
 * Version:
 * 0.1  Start Bit, and Control Byte ... check
 * 0.2  /ACK NAK and Stop ... check!
 * 0.3  works+232
 *
 */
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 4000000 //4Mhz FRC internal osc
#define __delay_us(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define __delay_ms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))
#endif

#include 
#include 
#include 
#include 

//config bits
#pragma config FOSC=INTOSC, WDTE=OFF, PWRTE=ON, MCLRE=ON, CP=OFF, BOREN=OFF, CLKOUTEN=OFF, FCMEN=OFF
#pragma config WRT=OFF, STVREN=OFF, LVP=OFF


#define _XTAL_FREQ 4000000 //defined for delay
#define device_address  0b1001000       // unused for now

    unsigned int ACK_bit;
    int i, x;   //garbage flags
    long int tempi, tempn, tempx, tempy, temp10, temp25;
    unsigned char byte, tempbyte1, tempbyte2;
    unsigned char StatusByte;
    unsigned char RESP1Byte, RESP2Byte, RESP3Byte, RESP4Byte, RESP5Byte;
    unsigned char RESP6Byte, RESP7Byte, RESP8Byte, RESP9Byte, RESP10Byte;
    unsigned char RESP11Byte, RESP12Byte, RESP13Byte, RESP14Byte;
    char buf[10];

void init_io(void) {

    ANSELA = 0x00; // all port A pins are digital I/O
    ANSELB = 0x00; // all port A pins are digital I/O
    ANSELC = 0x00; // all port B pins are digital I/O

    TRISAbits.TRISA0 = 0; // keypad strobe 1
    TRISAbits.TRISA1 = 0; // keypad strobe 2
    TRISAbits.TRISA2 = 0; // RADIO /RST
    TRISAbits.TRISA3 = 1; // /MCLR
    TRISAbits.TRISA4 = 0; // LCD RS
    TRISAbits.TRISA5 = 0; // LCD EN

    TRISBbits.TRISB4 = 1; // RB4 I2C SDA, has to be set as an input
    TRISBbits.TRISB5 = 1; // RB5 NC (RESERVED RS232)
    TRISBbits.TRISB6 = 1; // RB6 I2C SCLK, has to be set as an input
    TRISBbits.TRISB7 = 0; // RB7 NC (RESERVED RS232)

    TRISCbits.TRISC0 = 0; // LCD D4
    TRISCbits.TRISC1 = 0; // LCD D5
    TRISCbits.TRISC2 = 0; // LCD D6
    TRISCbits.TRISC3 = 0; // LCD D7
    TRISCbits.TRISC4 = 1; // button col 1
    TRISCbits.TRISC5 = 1; // button col 2
    TRISCbits.TRISC6 = 1; // button col 3
    TRISCbits.TRISC7 = 1; // button col 4
}

/*
 *  LCD Interface Functions
 *  standard 44780 format 2 lines
 */

void lcd_strobe (void)  //TOGGLE LCD_EN
{
    LATAbits.LATA5 = 0;
    __delay_ms(20);
    LATAbits.LATA5 = 1;
}

/* write a byte to the LCD in 4 bit mode */

void lcd_write(unsigned char c)
{
	LATC = c >> 4;
	lcd_strobe();
	LATC = c;
	lcd_strobe();
        __delay_us(100);
}

/*
 * 	Clear and home the LCD
 */

void lcd_clear(void)
{
	LATAbits.LATA4 = 0;
	lcd_write(0x1);
        __delay_ms(2);
}


/* write a string of chars to the LCD */

void lcd_puts(const char * s)
{
	LATAbits.LATA4 = 1;	// write characters
	while(*s)
		lcd_write(*s++);
}

/*
 * Go to the specified position
 */

void lcd_goto(unsigned char pos)
{
	LATAbits.LATA4 = 0;
	lcd_write(0x80+pos);
}

/*
 *      Write 16 spaces on LCD 2 to avoid blanking, (ugly CLEAR effect)
 *      this is slow but work for my needs
 */

void    lcd_clrline1(void)
{
    lcd_goto(0);
    lcd_puts("                ");
    lcd_goto(0);
}

void    lcd_clrline2(void)
{
    lcd_goto(40);
    lcd_puts("                ");
    lcd_goto(40);
}

/* initialise the LCD - put into 4 bit mode */

void lcd_init(void)
{
	LATAbits.LATA4 = 0;	// write control bytes
        LATC = 0x03;
        __delay_ms(150);         //power on delay
	lcd_strobe();
        __delay_ms(5);
	lcd_strobe();
        __delay_ms(5);
	lcd_strobe();
        __delay_ms(5);
	LATC = 0x02;             // set 4 bit mode
        __delay_ms(5);
	lcd_strobe();
        __delay_ms(5);
	lcd_write(0x28);	// 4 bit mode, 1/16 duty, 5x8 font
	lcd_write(0x08);	// display off
	lcd_write(0x0C);	// display on cursor+blink off
	lcd_write(0x06);	// entry mode
}

/*
 *  I2C Functions
 *
 */

void I2C_ACK(void)
{
   PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
   SSP1CON2bits.ACKDT=0;        // clear the Acknowledge Data Bit - this means we are sending an Acknowledge or 'ACK'
   SSP1CON2bits.ACKEN=1;        // set the ACK enable bit to initiate transmission of the ACK bit to the serial eeprom
   while(!PIR1bits.SSP1IF);    // Wait for interrupt flag to go high indicating transmission is complete
}

void Send_I2C_Data(unsigned int databyte)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSPBUF = databyte;              // send databyte
    while(!PIR1bits.SSP1IF);    // Wait for interrupt flag to go high indicating transmission is complete
}

unsigned char RX_I2C_Data (void)
{

    RCEN = 1;               //
    while( RCEN ) continue;
    while( !BF ) continue;
    byte = SSPBUF;
   return byte;
}

void I2C_Control_Write(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSP1BUF = 0xC6;             // send the control byte 4707 Addr w/ SEN=1
    while(!PIR1bits.SSP1IF)     // Wait for interrupt flag to go high indicating transmission is complete
        {
        i = 1;
          // place to add a breakpoint if needed
        }
    PIR1bits.SSP1IF=0;

}

void I2C_Control_Read(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSP1BUF = 0xC7;             // send the control byte
    while(!PIR1bits.SSP1IF)     // Wait for interrupt flag to go high indicating transmission is complete
        {
        i = 1;
          // place to add a breakpoint if needed
        }
    PIR1bits.SSP1IF=0;
   }

void I2C_Start_Bit(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSPCON2bits.SEN=1;          // send start bit
    while(!PIR1bits.SSP1IF)    // Wait for the SSPIF bit to go back high before we load the data buffer
        {
        i = 1;
        }
    PIR1bits.SSP1IF=0;
}

void I2C_check_idle()
{
    unsigned char byte1; // R/W status: Is a transfer in progress?
    unsigned char byte2; // Lower 5 bits: Acknowledge Sequence, Receive, STOP, Repeated START, START

    do
    {
        byte1 = SSPSTAT & 0x04;
        byte2 = SSPCON2 & 0x1F;
    } while( byte1 | byte2 );
}
/*
 * Send the repeated start message and wait repeated start to finish.
 */
void I2C_restart()
{
    I2C_check_idle();
    RSEN = 1; // Reinitiate start
    while( RSEN ) continue;
}

void I2C_Stop_Bit(void)
{
    PIR1bits.SSP1IF=0;          // clear SSP interrupt bit
    SSPCON2bits.PEN=1;          // send stop bit
    while(!PIR1bits.SSP1IF)
    {
        i = 1;
        // Wait for interrupt flag to go high indicating transmission is complete
    }
}

void I2C_NAK(void)
{
    PIR1bits.SSP1IF=0;           // clear SSP interrupt bit
    SSP1CON2bits.ACKDT=1;        // set the Acknowledge Data Bit- this means we are sending a No-Ack or 'NAK'
    SSP1CON2bits.ACKEN=1;        // set the ACK enable bit to initiate transmission of the ACK bit to the serial eeprom
    while(!PIR1bits.SSP1IF)     // Wait for interrupt flag to go high indicating transmission is complete
    {
        i = 1;
    }
}

/*
 *  Si4707 WB RX Functions
 *
 */

void Tune400(void)
{
//162400	64960	FDC0

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();                 // send control byte

    Send_I2C_Data(0x50);                 //Tune Frequency
    Send_I2C_Data(0x00);                 //0x00
    Send_I2C_Data(0xFD);                 //
    Send_I2C_Data(0xC0);                 //...

    I2C_Stop_Bit();

    __delay_ms(1000);					//tune delay
}

void Tune425(void)
{
//162425	64970	FDCA

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();                 // send control byte

    Send_I2C_Data(0x50);                 //Tune Frequency
    Send_I2C_Data(0x00);                 //0x00
    Send_I2C_Data(0xFD);                 //
    Send_I2C_Data(0xCA);                 //...

    I2C_Stop_Bit();

    __delay_ms(1000);					//tune delay
}

void Tune450(void)
{
//162450	64980	FDD4

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();                 // send control byte

    Send_I2C_Data(0x50);                 //Tune Frequency
    Send_I2C_Data(0x00);                 //0x00
    Send_I2C_Data(0xFD);                 //
    Send_I2C_Data(0xD4);                 //...

    I2C_Stop_Bit();

    __delay_ms(1000);					//tune delay
}

void Tune475(void)
{
//162475	64990	FDDE

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();                 // send control byte

    Send_I2C_Data(0x50);                 //Tune Frequency
    Send_I2C_Data(0x00);                 //0x00
    Send_I2C_Data(0xFD);                 //
    Send_I2C_Data(0xDE);                 //...

    I2C_Stop_Bit();

    __delay_ms(1000);					//tune delay
}

void Tune500(void)
{
//162500	65000	FDE8

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();                 // send control byte

    Send_I2C_Data(0x50);                 //Tune Frequency
    Send_I2C_Data(0x00);                 //0x00
    Send_I2C_Data(0xFD);                 //
    Send_I2C_Data(0xE8);                 //...

    I2C_Stop_Bit();

    __delay_ms(1000);					//tune delay
}

void Tune525(void)
{
//162525	65010	FDF2

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();                 // send control byte

    Send_I2C_Data(0x50);                 //Tune Frequency
    Send_I2C_Data(0x00);                 //0x00
    Send_I2C_Data(0xFD);                 //
    Send_I2C_Data(0xF2);                 //...

    I2C_Stop_Bit();

    __delay_ms(1000);					//tune delay
}

void Tune550(void)
{
//162550	65020	FDFC

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();                 // send control byte

    Send_I2C_Data(0x50);                 //Tune Frequency
    Send_I2C_Data(0x00);                 //0x00
    Send_I2C_Data(0xFD);                 //
    Send_I2C_Data(0xFC);                 //...

    I2C_Stop_Bit();

    __delay_ms(1000);					//tune delay
}

void VolumeUp(void)
{
//future use
}

void VolumeDown(void)
{
//future use
}

void VolumeMAX (void)
{
    // Reset Volume
}
void VolumeMUTE (void)
{
    //Mute Sound

}

void CheckStatus (void)
{
/*
 * STATUS BYTE
 *	[7] CTS	Clear to Send.
 *	0 = Wait before sending next command.
 *	1 = Clear to send next command.

 *	[6] ERR	Error.
 *	0 = No error
 *	1 = Error

 *	5:4 Reserved Values may vary.

 *	[3] RSQINT	Received Signal Quality Interrupt.
 *	0 = Received Signal Quality measurement has not been triggered.
 *	1 = Received Signal Quality measurement has been triggered.

 *	[2] SAMEINT	SAME Interrupt (Si4707 Only).
 *	0 = SAME interrupt has not been triggered.
 *	1 = SAME interrupt has been triggered.

 *	[1] ASQINT	Audio Signal Quality Interrupt.
 *	0 = Audio Signal Quality measurement has not been triggered.
 *	1 = Audio Signal Quality measurement has been triggered.

 *	[0] STCINT	Seek/Tune Complete Interrupt.
 *	0 = Tune complete has not been triggered.
 *	1 = Tune complete interrupt has been triggered.

*/
//0x52 RX_STATUS
//STATUS, RESP1 (VALID), RESP2 FREQ_H, RESP3 FREQ_L, RESP4 RSSI, RESP5 SNR

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();
    Send_I2C_Data(0x52);                //TUNE STATUS
    Send_I2C_Data(0x00);                //DONT CLEAR INT

    I2C_restart();
    I2C_Control_Read();

    RX_I2C_Data();                      //STATUS
	StatusByte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //VALID
	RESP1Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //FREQ1
	RESP2Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //FREQ2
	RESP3Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //RSSI
	RESP4Byte = byte;
    I2C_ACK();

    RX_I2C_Data();                      //SNR
	RESP5Byte = byte;
    I2C_NAK();                          //NAK

	I2C_Stop_Bit();                     // Send Stop Bit

//Update Freq Display
//Update RSSI
}



CheckFlag(unsigned value, unsigned bitindex)
{
//1=0x000000_0
//CheckFlag(BYTE,1);

    return (value & (1 << bitindex)) != 0;
}


void CheckSAME(void)
{
//0x54   SAME_STATUS
//STATUS, ARG1, ARG2, STATUS, RESP1-RESP13.
//
//ARG1 0:INTACK 1:CLRBUF
//ARG2 READ_ADDR
//3:RSQINT 2:SAMEINT 1:ASQINT 0:STCINT

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();
    Send_I2C_Data(0x54);                //SAME STATUS
    Send_I2C_Data(0x00);                //DONT CLEAR INT
	Send_I2C_Data(0x00);                //Start location

    I2C_restart();
    I2C_Control_Read();

    RX_I2C_Data();                      //STATUS
	StatusByte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP1Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP2Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP3Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP4Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP5Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP6Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP7Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP8Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP9Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP10Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP11Byte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //
	RESP12Byte = byte;
    I2C_ACK();

    RX_I2C_Data();                      //
	RESP13Byte = byte;
    I2C_NAK();                          //NAK

	I2C_Stop_Bit();                     // Send Stop Bit

        if (CheckFlag(StatusByte,2))
            i=1;    //TODO
}


void ResetSAME(void)
{
//0x54   SAME_STATUS
//STATUS, ARG1, ARG2, STATUS, RESP1-RESP13.
//ARG1 0:INTACK 1:CLRBUF
//ARG2 READ_ADDR
//3:RSQINT 2:SAMEINT 1:ASQINT 0:STCINT

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();
    Send_I2C_Data(0x54);                //SAME STATUS
    Send_I2C_Data(0x03);                //Dump Buffer and Reset SAME Int.
	Send_I2C_Data(0x00);                //Start location

    I2C_restart();
    I2C_Control_Read();

    RX_I2C_Data();                      //STATUS
	StatusByte = byte;
    I2C_ACK();

	RX_I2C_Data();                      //don't care about the rest..
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

	RX_I2C_Data();                      //
    I2C_ACK();

    RX_I2C_Data();                      //
    I2C_NAK();                          //NAK

	I2C_Stop_Bit();                     // Send Stop Bit
}


void Monitor(void)
{
    //TODO

}

void Standby(void)
{
    //TODO

}

MultiFunction()
{
LATAbits.LATA0=0;   //TODO
LATAbits.LATA1=1;

__delay_ms(2000);

	if (LATCbits.LATC3)
	Monitor();
	else
	Standby();

}

poll_buttons()      //TODO
{
//check buttons for switch. no need for debounce, polling is long in the case of keydown.

LATAbits.LATA0=1;
LATAbits.LATA1=0;
__delay_ms(5);

if (LATCbits.LATC4)
	Tune400();
if (LATCbits.LATC5)
	Tune425();
if (LATCbits.LATC6)
	Tune450();
if (LATCbits.LATC7)
	Tune475();

LATAbits.LATA0=0;
LATAbits.LATA1=1;
__delay_ms(5);

if (LATCbits.LATC4)
	Tune500();
if (LATCbits.LATC1)
	Tune525();
if (LATCbits.LATC2)
	Tune550();
if (LATCbits.LATC3)
	MultiFunction();
}

void RST_4707(void)
{
        LATAbits.LATA2 = 0;
        __delay_ms(50);
        LATAbits.LATA2 = 1;
}

void display_missing(void)
{
    lcd_clrline1();

    lcd_puts("Si4707 missing.");
}

void display_freq(void)
{
    lcd_clrline1();

    lcd_puts("FREQ: ");
    CheckStatus();
    //RESP4Byte
    temp25 = 25;
    temp10 = 10;
    tempn = RESP2Byte;
    tempy = 256;
    tempx = RESP3Byte;
    tempi = tempn*tempy;
    tempi = tempi+tempx;
    tempi = tempi*temp25;
    tempi = tempi/temp10;

    ltoa(buf,tempi,10);  //long conversion to buffer
    lcd_puts(buf);
    lcd_puts(" KHz");
}

int main(void) {

    OSCCONbits.IRCF = 0x0d;     //set OSCCON IRCF bits to select OSC frequency 4MHz
    OSCCONbits.SCS = 0x02;
    OPTION_REGbits.nWPUEN = 0;  //enable weak pullups (each pin must be enabled individually)

    init_io();

    __delay_ms(250);            //let the power settle

     lcd_init();
    __delay_ms(10);
     lcd_clear();

                                //display test message
    lcd_puts("iradan.com");
    lcd_goto(40);

    TRISBbits.TRISB6 = 1;

    SSPSTATbits.SMP = 1;
    SSPCONbits.SSPM=0x08;       // I2C Master mode, clock = Fosc/(4 * (SSPADD+1))
    SSPCONbits.SSPEN=1;         // enable MSSP port
    SSPADD = 0x27;              //figure out which one you can ditch sometime (probably either)
    SSP1ADD = 0x27;             // 100KHz
                                //0x09 = 100KHz
    // **************************************************************************************

    RST_4707();

    __delay_ms(100);                    // let everything settle.

    I2C_Start_Bit();                    // send start bit
    I2C_Control_Write();                // send control byte with read set
 
    x=0;                                // temp feature, TODO
    if (!SSP1CON2bits.ACKSTAT)
    x=1;                 //device there? /ACked?

    Send_I2C_Data(0x01);                //power up
    Send_I2C_Data(0x53);                //command per AN332
    Send_I2C_Data(0x05);
    I2C_Stop_Bit();

    __delay_ms(1000);                     //power up delay...

    I2C_Start_Bit();                     // send start bit
    I2C_Control_Write();                 // send control byte
    Send_I2C_Data(0x50);                 //Tune Frequency
    Send_I2C_Data(0x00);                 //0x00
    Send_I2C_Data(0xFD);                 //65020 (162.550)
    Send_I2C_Data(0xFC);                 //... FDFC
    I2C_Stop_Bit();

    __delay_ms(1000);                    //tuning delay

    if (x==1)
        display_freq();
    else    
        display_missing();

    lcd_clrline2();   //clear LCD line 2 by writting " " and return
    lcd_puts("RSSI: ");
    tempi = RESP4Byte;
    ltoa(buf,tempi,10);  //long conversion to buffer
    lcd_puts(buf);

    while (1) {
        poll_buttons();
        i=1;    //  do nothing for now..
        __delay_ms(100);                      // delay.. just because
    }
    return;
}

C Electronics Microcontrollers PIC Programming

I2C with the 16F1509 and TCN75A

What are you looking at? More code. Joy!

I know I’ve been doing a lot of these code tidbits lately but it’s what has been driving me to sit at the bench. This is my first I2C project.. I pulled heavily from many sources of snippets, documentation and projects; microchip forums (*some of it wrong*), app data, both pieces of product data and a lot of trial and error… mostly error.

In a run up to my weather radio project I needed to get familiar with using I2C with the XC8 compiler. I’ve been focusing most of my experimenting with the 16F1509 lately so I’ll be sticking with it again here. I switched to the ‘1509 from the 16F628A. In the future I have the 16F916 I have plans for and then I’ll go back to the 18F series to work on the USB project in the no-so-distant future.

Before I prepared to working on this project Jayson Tautic mentioned you don’t work on I2C without a logic analyzer; I’ve never known a person to be so absolutely correct about anything, ever. So, I bought one. My little logic analyzer was absolutely required, I know I wouldn’t have gotten this finished without it. You’ll note the screen shot… catching these little burps with a scope would have been pretty difficult.

Successful read of the TCN75A
Successful read of the TCN75A

I’m really thankful he recommended the Saleae. It was on the top of my list but his recommendation sold me on pulling the trigger.

This article is not to explain or go into the I2C protocol, there are a ton of “101” articles out there.. just pick one, or two, or three. I started with this one from embedded lab.

I picked the TCN75A temp sensor for this I2C test. I had a BMP085 but I accidentally blew it up on 5V when I threw my RS-232 board on and forgot I had the sensor still plugged in… Ooops! The BMP085 is a 3.3V device. I really need to buy a dual breadboard power supply one of these days!

In short to communicate with this TCN75A you write the “Write” control byte to the I2C bus, you look for your /ACK set your pointer and set the configuration byte… wait “forever” (240ms according to DS21935A) for the conversion, write the write control byte address, set the pointer, restart, write the “read” control byte and grab your two bytes of temperature data. You should /ACK the first byte of received data.. NAK the second. I made the mistake of /ACKing both bytes.. that causes the I2C slave to hang the SDA low..

In slightly more detail:

START I2C
Send Address 0x90
Send 0x01 conf pointer
Send 0xE1 “one shot” 12bit conversion
STOP I2C
…wait
START I2C
Send Address 0x90
0x00
RESTART I2C
Send Address 0x91
READ I2C //HIGH
ACK
READ I2C //LOW
NAK
STOP I2C

 

The circuit... TCN75 on the bottom left of the breadboard. The PIC microcontroller is the think the PICKit3 is plugged into and I'm dumping the raw data to RS-232 (bottom right).
The circuit… TCN75 on the bottom left of the breadboard. The PIC microcontroller is the think the PICKit3 is plugged into and I’m dumping the raw data to RS-232 (bottom right).

 

So it worked… I dumped the raw info to the UART. I didn’t really feel like dumping it to an LCD or anything since I’d be more likely to use this for telemetry than for a local display. It’s a good starting block to a vasic project. I’ll add the code on my code sample page later on this weekend but for now you can find it below….

The code:

/* 
 * File: newmain.c
 * Author: Charles M Douvier
 * Contact at: http://iradan.com
 *
 * Created on January 26, 2014, 12:00 PM
 *
 * Target Device:
 * 16F1509 on Tautic 20 pin dev board
 *
 * Project:
 * I2C Testing with the TCN75A
 *
 * Version:
 * 0.1 Start Bit, and Control Byte ... check
 * 0.2 /ACK NAK and Stop ... check!
 * 0.3 works+232
 *
 */
#ifndef _XTAL_FREQ
#define _XTAL_FREQ 4000000 //4Mhz FRC internal osc
#define __delay_us(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000000.0)))
#define __delay_ms(x) _delay((unsigned long)((x)*(_XTAL_FREQ/4000.0)))
#endif
#include <xc.h>
//config bits
#pragma config FOSC=INTOSC, WDTE=OFF, PWRTE=ON, MCLRE=ON, CP=OFF, BOREN=OFF, CLKOUTEN=OFF, FCMEN=OFF
#pragma config WRT=OFF, STVREN=OFF, LVP=OFF
//IESO=OFF
#define _XTAL_FREQ 4000000 //defined for delay
#define device_address 0b1001000 // TCN75A Address (A012 =0)
unsigned int ACK_bit;
 int i;
 unsigned char byte, tempbyte1, tempbyte2;
void init_io(void) {
ANSELA = 0x00; // all port A pins are digital I/O
 ANSELB = 0x00; // all port A pins are digital I/O
 ANSELC = 0x00; // all port B pins are digital I/O
 TRISAbits.TRISA0 = 1; // output
 TRISAbits.TRISA1 = 1; // output
 TRISAbits.TRISA2 = 1; // output
 TRISAbits.TRISA3 = 1; // output
 TRISAbits.TRISA4 = 1; // output
 TRISAbits.TRISA5 = 1; // output
TRISBbits.TRISB4 = 1; // RB4 I2C SDA, has to be set as an input
 TRISBbits.TRISB5 = 1; // RB5 = nc
 TRISBbits.TRISB6 = 1; // RB6 I2C SCLK, has to be set as an input
 TRISBbits.TRISB7 = 0; // RS232 TX
TRISCbits.TRISC0 = 0; // output
 TRISCbits.TRISC1 = 0; // output
 TRISCbits.TRISC2 = 0; // output
 TRISCbits.TRISC3 = 0; // output
 TRISCbits.TRISC4 = 0; // output
 TRISCbits.TRISC5 = 0; // output
 TRISCbits.TRISC6 = 0; // input
 TRISCbits.TRISC7 = 0; // input
 LATCbits.LATC0 = 1;
 LATCbits.LATC1 = 0;
 LATCbits.LATC2 = 0;
}
void uart_xmit(unsigned int mydata_byte) {
while(!TXSTAbits.TRMT); // make sure buffer full bit is high before transmitting
 TXREG = mydata_byte; // transmit data
}
void serial_init(void)
{
// calculate values of SPBRGL and SPBRGH based on the desired baud rate
 //
 // For 8 bit Async mode with BRGH=0: Desired Baud rate = Fosc/64([SPBRGH:SPBRGL]+1)
 // For 8 bit Async mode with BRGH=1: Desired Baud rate = Fosc/16([SPBRGH:SPBRGL]+1)

 TXSTAbits.BRGH=1; // select low speed Baud Rate (see baud rate calcs below)
 TXSTAbits.TX9=0; // select 8 data bits
 TXSTAbits.TXEN = 1; // enable transmit
 RCSTAbits.SPEN=1; // serial port is enabled
 RCSTAbits.RX9=0; // select 8 data bits
 RCSTAbits.CREN=1; // receive enabled
SPBRGL=25; // here is calculated value of SPBRGH and SPBRGL
 SPBRGH=0;
PIR1bits.RCIF=0; // make sure receive interrupt flag is clear
 PIE1bits.RCIE=1; // enable UART Receive interrupt
 INTCONbits.PEIE = 1; // Enable peripheral interrupt
 INTCONbits.GIE = 1; // enable global interrupt
__delay_ms(50); // give time for voltage levels on board to settle
 uart_xmit('R'); // transmit some data
 uart_xmit('S');
 uart_xmit('T');
}
void I2C_ACK(void)
{
 PIR1bits.SSP1IF=0; // clear SSP interrupt bit
 SSP1CON2bits.ACKDT=0; // clear the Acknowledge Data Bit - this means we are sending an Acknowledge or 'ACK'
 SSP1CON2bits.ACKEN=1; // set the ACK enable bit to initiate transmission of the ACK bit to the serial eeprom
 while(!PIR1bits.SSP1IF); // Wait for interrupt flag to go high indicating transmission is complete
}
void Send_I2C_Data(unsigned int databyte)
{
 PIR1bits.SSP1IF=0; // clear SSP interrupt bit
 SSPBUF = databyte; // send databyte
 while(!PIR1bits.SSP1IF); // Wait for interrupt flag to go high indicating transmission is complete
}
unsigned char RX_I2C_Data (void)
{
RCEN = 1; // 
 while( RCEN ) continue;
 while( !BF ) continue;
 byte = SSPBUF;
 return byte;
}
void I2C_Control_Write(void)
{
 PIR1bits.SSP1IF=0; // clear SSP interrupt bit
 SSP1BUF = 0x90; // send the control byte (90 TCN75, EF BMP085)
 while(!PIR1bits.SSP1IF) // Wait for interrupt flag to go high indicating transmission is complete
 {
 i = 1;
 // place to add a breakpoint if needed
 }
 PIR1bits.SSP1IF=0;
}
void I2C_Control_Read(void)
{
 PIR1bits.SSP1IF=0; // clear SSP interrupt bit
 SSP1BUF = 0x91; // send the control byte (90 TCN75, EF BMP085)
 while(!PIR1bits.SSP1IF) // Wait for interrupt flag to go high indicating transmission is complete
 {
 i = 1;
 // place to add a breakpoint if needed
 }
 PIR1bits.SSP1IF=0;
 }
void I2C_Start_Bit(void)
{
 PIR1bits.SSP1IF=0; // clear SSP interrupt bit
 SSPCON2bits.SEN=1; // send start bit
 while(!PIR1bits.SSP1IF) // Wait for the SSPIF bit to go back high before we load the data buffer
 {
 i = 1;
 }
 PIR1bits.SSP1IF=0;
}
void I2C_check_idle()
{
 unsigned char byte1; // R/W status: Is a transfer in progress?
 unsigned char byte2; // Lower 5 bits: Acknowledge Sequence, Receive, STOP, Repeated START, START
do
 {
 byte1 = SSPSTAT & 0x04;
 byte2 = SSPCON2 & 0x1F;
 } while( byte1 | byte2 );
}
/*
 * Send the repeated start message and wait repeated start to finish.
 */
void I2C_restart()
{
 I2C_check_idle();
 RSEN = 1; // Reinitiate start
 while( RSEN ) continue;
}
void I2C_Stop_Bit(void)
{
 PIR1bits.SSP1IF=0; // clear SSP interrupt bit
 SSPCON2bits.PEN=1; // send stop bit
 while(!PIR1bits.SSP1IF)
 {
 i = 1;
 // Wait for interrupt flag to go high indicating transmission is complete
 }
}
void I2C_NAK(void)
{
 PIR1bits.SSP1IF=0; // clear SSP interrupt bit
 SSP1CON2bits.ACKDT=1; // set the Acknowledge Data Bit- this means we are sending a No-Ack or 'NAK'
 SSP1CON2bits.ACKEN=1; // set the ACK enable bit to initiate transmission of the ACK bit to the serial eeprom
 while(!PIR1bits.SSP1IF) // Wait for interrupt flag to go high indicating transmission is complete
 {
 i = 1;
 }
}
int main(void) {
OSCCONbits.IRCF = 0x0d; //set OSCCON IRCF bits to select OSC frequency 4MHz
 OSCCONbits.SCS = 0x02; 
 OPTION_REGbits.nWPUEN = 0; //enable weak pullups (each pin must be enabled individually)
init_io();
 serial_init();
SSPCONbits.SSPM=0x08; // I2C Master mode, clock = Fosc/(4 * (SSPADD+1))
 SSPCONbits.SSPEN=1; // enable MSSP port
 SSPADD = 0x09; //figure out which one you can ditch sometime (probably either)
 SSP1ADD = 0x09; // 100KHz
 // **************************************************************************************
 __delay_ms(50); // let everything settle.
 I2C_Start_Bit(); // send start bit
 I2C_Control_Write(); // send control byte with read set
if (!SSP1CON2bits.ACKSTAT)
 LATCbits.LATC1 = 0; //device /ACked?
Send_I2C_Data(0x01); //pointer
 Send_I2C_Data(0xE1); //1 shot, 12bit res
 I2C_Stop_Bit();

 __delay_ms(500); //wait for conversion
I2C_Start_Bit(); // send start bit
 I2C_Control_Write(); // send control byte with read set
 if (!SSP1CON2bits.ACKSTAT)
 LATCbits.LATC1 = 0;
 Send_I2C_Data(0x00); //pointer
I2C_restart(); //restart
 I2C_Control_Read();
 RX_I2C_Data(); //read high
 tempbyte1=byte;
 I2C_ACK(); //ACK
 RX_I2C_Data(); //read low
 tempbyte2=byte;
 I2C_NAK(); //NAK
 //I2C_restart();
 I2C_Stop_Bit(); // Send Stop Bit
uart_xmit(tempbyte1); //send data off raw by UART
 uart_xmit(tempbyte2);
 __delay_ms(1); // delay.. just because
while (1) {
 __delay_ms(500);
 LATCbits.LATC0 = 1; //blinky
 __delay_ms(500);
 LATCbits.LATC0 = 0;
 }
 return;
}