Works only without Zener diode?!?

[TomSchimana]

Hi.

I have assembled the ps2pico and have a question about it. I took the version which is for PS/2 Keyboards

I currently have the whole thing put together on a breadboard. It didn't work initially. After some tests, I figured out to remove the Zener diode between GPIO14 and Ground. The other one from GPIO17 to Ground is still in place.

After removing it, everything worked immediately. Now I'm concerned that I might face issues with overvoltage later on.

In the picture, you can see my wild setup. 😉
Inside the rectangle is the Zener diode from GPIO 17 to Ground, and where the arrow is pointing, I removed it.

On the VBUS, there is pretty much exactly 5 volts. If I measure GPIO 14 to Ground or even GPIO 17, it's 0.5?!?! Whether the Zener diode is connected or not. Maybe I'm doing something wrong or I assembled it incorrectly. The Zener diodes are 3.6V 5W.
When I place a 10K resistor between GPIO 14 and Ground, everything still works.

Should I just leave it or is something "wrong", even though it works without the diode?
Thanks in advance!

[No0ne]

I think the problem is that there are only 10k pull-ups on the board according to: http://land-boards.com/PiPicoMite01/PiPicoMite01_Rev2_Schematic.pdf
And the zener pulls down the voltage too much behind the second 10k.

But you could try the following:
use my other project https://github.com/No0ne/ps2x2pico/releases/tag/beta-0.8
and connect like this:
Board GND to Pico GND
Board 5V to Pico VBUS
Board J10 Pin 12 (=GP9) to Pico GPIO11
Board J10 Pin 11 (=GP8) to Pico GPIO12

This should work without any additional components.

[No0ne]

Here I've started another project for the picomite: https://github.com/No0ne/hid2cdc