HP41C with Rp Pico attached

[Tinue]

Thank you both. I realize that I highjack this thread, so if I am out of line please let me know. I need to interface with the HP C4103A, which is a 5V device. I read about the tolerance to 5V, but as written the RP2040 chip needs to have booted and switched the GPIO to "input", before 5V can be applied. It's a bit risky, when the C4103A is receiving IR on power up: If the C4103A boots up first it can damage the Pico.

I only have a 74AHC125 lying around. These are bus drivers, but can be used as level shifters. They work fine for shifting up, but I never tried them for shifting down. The data sheet hints at this to maybe be allowed, but it's not within spec.

I thought that you were maybe using a simple voltage divider, because I see lots of resistors in the video ;-)