Month: April 2014

Jayson Tautic had mentioned, on IRC the other day, a Fourth system with the ability to run on a PIC… that pretty cool (mad scientist stuff!). It prompted me to consider connectivity; I posted my progress on the recent Digi One SP project that came out of that on my last post.

It’s been noticed that Jayson sleeps far fewer hours than I do, this is further proof! At lightning speeds (maybe that’s why he sells a lightning sensor?) he has his Pi running ser2net which connects the internet to a terminal port and from there to the serial port of his PIC running FlashForth. Jayson has Forth running on an 18F14K22 on his 20pin dev board which can also be found on his tindie store. I have never reviewed/commented on someone else’s project but I thought this was extremely clever and demanded attention. He won’t admit it was much of course, he’s far to modest. What’s next? What does this open up for us 8-bit PIC developers? Well I tell you what.. I have some ideas you’ll see in the near future!

Today was a FR4-AIL day, again. Still no PCBs in the mail today; I suspect this will be a PITA because they never left the Oregon post office.

With that I wasn’t really in the mood for any “real” electronics today. Jayson Tautic mentioned he put Fourth on a PIC 18F14K22 which is pretty cool. It got me thinking, one thing and then another and on to connectivity which lead me digging into the old project bins.

I’m sure it’s been done over and over but it hasn’t been done by me; I’ll see if I can put a PIC online. Maybe a simple text game?

Out of the projects bin came a Rev A11 XPort… well an hour later it went right back into the box. I think the old versions weren’t really friendly for what I was thinking.. next attempt was a Digi One SP. I bought one off eBay a while back; I’m way more familiar with these as I had installed a couple of them for a radio station for some telemetry.

The whole set up on the Digi One SP is pretty easy; logon by web browser, set up a static IP, etc, etc… the only tricky part was Serial Port set up. It would seem the Serial Port Profile setup should be to the “Modem In” profile but in fact to initiate a connection from ethernet you need to choose “Modem Out”. No problem..

So this is how I tested the setup:

I used RealTerm to connect to the serial port, it’s ANSI emulation but I used ASCII so I could the control characters. I connected my EdgePort (USB<–>RS232) through a null modem adapter to the DigiOne SP. On the ethernet side I used Putty; with a little poking I connected to the Digi One with “RAW” TCP to port 2001.

The connection tidbits are done, now I have to order a wireless bridge so I can get an ethernet port down in my bench (all wifi)… in the mean-time I also set up dyndns with my router because we don’t have a static IP address… TBC.

To be honest, I have never considered using the PIC 16F1509 digital to analog converter before. I was considering integrating a DAC internally or externally to a microcontroller for my brother’s synth project. I started on the microchip site and found a number of smaller PICs, 12F1501.. 16F1503, that had a 5bit DAC. The 16F753 has a 9bit and the 16F17* series has a 8bit DAC. I stuck with the old standby 16F1509 as I needed a serial port for MIDI and I had it sitting on an easy-to-use dev board. I ordered a 16F17* series PIC a while back because they have some interesting peripherals and I will probably build a board around it for the resolution.

Turns out the DAC is probably the easiest peripheral I’ve used on the PIC. It took me longer to wait for the PICKit to update from 18F configuration to 16F. BUT.. if you’re having issues.. here you go:

A simple voltage follower (or however you want to buffer the output) is needed on the DAC output. It’s not designed to drive anything.

Don’t expect screaming speeds out of this thing…it’s just not going to happen. I ran mine up to 1.3KHz, which is more than enough for what I’m trying to accomplish. If you put an A/D converter in you could use that to control your ramp speed and you’d have yourself a nice driver for your VCO input on test equipment with properly conditioned output.

The code:

/*
* File: main.c
* Author: Charles M Douvier
* Contact at: http://iradan.com
*
* Created on April 13, 2014, 1:14 PM
*
* Target Device:
* 16F1509 on Tautic 20 pin dev board
*
* Project: DAC ramp test
*
* Version:
* 1.0
*
*/
#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=OFF, MCLRE=ON, CP=OFF, BOREN=ON, CLKOUTEN=OFF, IESO=OFF, FCMEN=OFF
#pragma config WRT=OFF, STVREN=OFF, LVP=OFF

#define _XTAL_FREQ 4000000 //defined for delay

int x; //DAC counter

/*
*
*/
void init_io(void) {
TRISAbits.TRISA0 = 0; // output
TRISAbits.TRISA1 = 0; // output
TRISAbits.TRISA2 = 0; // DAC2
TRISAbits.TRISA3 = 0; // output
TRISAbits.TRISA4 = 0; // output
TRISAbits.TRISA5 = 0; // output
// TRISAbits.TRISA6 = 0; // output
// TRISAbits.TRISA7 = 0; // output

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

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

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

void init_dac(void)
{
DACCON0bits.DACPSS = 0; //VDD ref
DACCON0bits.DACOE2 = 1; //output 2 enable (RA2)
DACCON0bits.DACEN = 1; //enable DAC
}

int main(void) {

// set up oscillator control register, using internal OSC at 4MHz.
OSCCONbits.IRCF = 0x0d; //set OSCCON IRCF bits to select OSC frequency 4MHz
OSCCONbits.SCS = 0x02; //set the SCS bits to select internal oscillator block
OPTION_REGbits.nWPUEN = 0; // enable weak pullups (each pin must be enabled individually)

init_io();
init_dac();

x = 0;

while (1) {

for (x = 0; x < 31; ++x)
{ //DAC is 5 bit
DACCON1bits.DACR = x; //dump count into DAC value
__delay_us(25);
}

}
return (EXIT_SUCCESS);
}