Hi Ian, you are quite correct, I could not find a diagram of the keyboard the other day, so did not see thatDon't you have this backwards? The LED drivers are open collector - i.e. you switch them to ground to enable the LED - the common 5V on pin 16 of SK3 is the positive side of every LED - you can see this most clearly with the power LED via R71 directly to ground. R72 you mention is on the cathode side of the drive LED. From your Pi GPIO, you could control the LED through an NPN transistor (e.g. 2N3904) connected to the low side (SEL0* side) of R72.
, but looking at the datasheet for the 82C711 it has an open drain output for the Drive0 pin and it's active low. Sorry if I misled anyone. Yes I would recommend using a transistor buffer stage, but this is probably a bit more involved now. I'm guessing that code running on the Pi is probably designed to switch the LED directly. In which case it would pull the GPIO pin low to switch the LED on, there does not seem to be an "open" mode that I can see. As far as I can see the max sink current is still 16mA. Providing a suitable current limiting resister is chosen there should not be a problem. Lastly I think it would make sense to configure the Pi GPIO to use 5V.Statistics: Posted by kfro — Fri Jan 03, 2025 10:32 pm