[Edit: I’ve added the .asm code in the “Code” page in the menu above. Below you can find the .HEX file for easy programming]
A successful test on my WWVB signal generator. I’m going to shy away from calling it a transmitter because I don’t think there is any allowances for any broadcasting on 60KHz, so to stay legal I would imagine you’d need to conform to part 15, shield everything, use an attenuator and dump the signal into a shielded box with the clock? I somehow doubt the FCC checks up on sub-mW transmissions on 60KHz though.
The concept is simple, 1 baud rate transmission of a 60 frame packet. The amplitude shift keying (ASK) system WWVB transmits is recreated using a CMOS CD4066 switch. Dump a 60KHz sine wave (keeping in mind maximum input/output signal specifications) into one of the switch ports. Use the output on PORTB.0 of the PIC to control the switch and the other side of the switch goes to you device under test (I used a couple feet of wire as an antenna and just placed the wire in the neighborhood of the clock receiver). It’s a no brainer. Check out the NIST site on WWVB if you want more details. I’ll probably re-port the code to a 12F629 when I get my new PICKit3 in and I’ll likely build a board with a 60KHz generator.. maybe I’ll even sell it on Tindie if I’m feeling ambitious.
The Test! I was getting my ass kicked earlier this week as my circuit was not working and it seemed like everything was just right. It did force me to really tweak my timing to make it within my range of error on being able to measure the exact pulse widths, I don’t know how precise it has to be but I assume that’s up to the algorithm decoding the signal. Turns out it wasn’t my code or circuit.. My $15 Fred Meyer “black friday special” atomic clock doesn’t work. It won’t receive the real WWVB (set up aligned with Boulder, CO away from electronics, blah blah). I was getting the proper signals out of the module, so I yanked the module out of the clock and hooked it up to a receiver designed by N0QBH. I mirrored his project here. He has a website for the project here. I used his schematic, ditched the need for the LCD and just grabbed my data off the RS232. Done! You can see a before and after output screenshot in the photos below.
My WWVB signal generator code (HEX) for a 16F628A is found here . Is it lame of my just to provide the HEX? yeah…. but all you need to do is hook up PORTB.0 to switching input of a 4066 with a signal generator feeding a 60KHz sine wave and you’re in business. (And a resistor pulling /MCLR (PORTA.5) up as well if that wasn’t obvious? I’m using the internal oscillator; no xtal needed). You are stuck with my fixed date of course.. which is why you want my assembly code right? No problem. Just ask… really (comment or e-mail). I don’t want to post it because I don’t really like comment trolls. This code is super BETA but at an acceptable starting point. Lots of opportunity for optimizing it as well. Why didn’t I improve on this code? Because I don’t need to. I’m just using it to test receivers I’ve purchased from the UK and I’ll be working on a project with those in a little while.
My time/date is static here is a snippet of the main line code:
CALL MARKER ;MARKER FRAME REFERENCE BIT CALL ONE ;40min CALL ZERO ;20min CALL ZERO ;10min CALL ZERO ;Reserved CALL ZERO ;8mins CALL ZERO ;4mins CALL ONE ;2mins CALL ZERO ;1mins CALL MARKER ;MARKER 1
… and so for some photos
The clock with the module removed, luckily they printed the pin diagram on the board. 5V, Gnd, PON, and TCO
Both the generator and receiver on the breadboard. The transistors form the RS-232 driver for the receiver.