so this didn't work out so well

A project log for a "true" in system programmer

I'm on vacation, not bored

davedarkodavedarko 11/21/2022 at 16:150 Comments

Image of PCB shows shortcuts on PCB connector that have been later fixed. Small board of 2cm x 4cm

twitter back log from 2020-10-24

"Time flies when you're trying to have fun with a two year old project. This is my take on an ISP for AVR and Attiny chips, than can power the target with 3V, 5V or translate to the target's voltage. I always wondered why the old version was sometimes shorting out and now I know.

The version before had POGO pins soldered directly to the pads (yes, they were mirrored for that). They were replaced with a "standard" 6 pin socket and this works fine. I was able to program plenty of targets with the new programmer. They just would not start.

With the POGO pins I never noticed that, because as soon as I was done programming with it, the target was powered on it's own and started fine. But now the reset line was held LOW because the reset pin turned into an INPUT.

The level-shifter I'm using is not bidirectional, but the direction of communication can be selected. So I lifted the pins and rewrote the USBASP firmware to change the direction whenever the red LED turns on and off (basically). Now nothing works anymore and I'm asking myself:

Should I change the schematics and find a bi-directional tri-state level-shifter? Or should I scope it and see if it's fixable with some delays?"

It seems to just work with the 5V circuitry and boots normally. Maybe it's behaving weird when it's 3.3V on the receiving side. Hm nope, also works with 3.3V. Maybe it was the target then, need to remember what I wanted to program back then.