New Project: AVR Programmer

I’ve been trying to break the Joust rebuild project into meaningful chunks. My recent attempt at designing a circuit for manufacture in EAGLE didn’t pan out; it seemed both too big, because I hadn’t yet breadboarded all the sub-circuits as a single large circuit, and at the same time too small, because it would have been little more than those simple sub- circuits that I had successfully breadboarded. I’d have taken a lot of risk to fabricate a fairly boring PCB.*

Rather than hem and haw about what exactly to build next for Project 8821, I decided to take Quinn’s approach and gain experience building a tool that I knew for sure I’d need:

This is going to be an AVR in-system programmer and XSVF player. True, I could buy a USBtiny clone for $10 on eBay or a real one in kit form for $26 shipped, and in fact I have plenty of gizmos capable of programming AVRs, but I don’t have anything that can also program CPLDs, the JTAG Whisperer notwithstanding. The JTAG Whisperer is great in a pinch, but I really need it to speak 3.3v and to not require my Arduino, which is often enlisted in other projects.

And unlike any other AVR programmer I’m aware of, mine won’t require that frickin’ ugly and gigantic 6-pin ISP ribbon cable. See that angled footprint in the lower-right corner? It’s going to have a socket sticking out of it at a right angle, so it’ll be a cinch to stick the board directly onto the target without any cable whatsoever. (Actually, by “whatsoever” I really mean it’ll need just a mini-USB cable on the other end, but those are so commonplace and compatible with other devices that I don’t consider it an inconvenience to keep one on my desk. So it doesn’t really count as a cable.)

I’ll be sending this board out for manufacture shortly. I’m excited about it because I honestly think it’ll be a pretty darn good AVR programmer. I might have a couple extra boards left over, so if you don’t have your own programmer and need one, leave a comment. I’ll probably need one more rev of the PCB and still have the small matter of writing the firmware, but I’d love to have others using my creations!

Update: made some changes (VCC separate from 8u2 supply, VCC-5V header removed) after great suggestions from frank26080115, who is also the creator of the USnooBie. Thanks, Frank!

*“Boring” is a strong word. If I stuck a serial port on that board, it’d be at least as fascinating as any home computer that existed before the video-capable Apple ][. But I want to stay on project target; if I added a serial port, then I’d have to write 6809 software to _use_ it. Given my self-imposed project constraint of avoiding getting into 6809 software and instead treating the Williams ROMs as an invariant, the serial port wouldn’t make sense.