HP41C with Rp Pico attached

[MeindertKuipers]

(12-02-2023 11:26 AM)Tinue Wrote:  I thought that you were maybe using a simple voltage divider, because I see lots of resistors in the video ;-)

For a quick and dirty downshifter you can use a voltage divider, as long as the speed is not too high. The resistors in my video are pullups on the output enables for the HP41 outout signals (towards the HCT125) to ensure that the outputs are not driven while the RP2040 is idle.
Using the '125 works well, its input high is low enough for the RP2040 outputs at 3.3V even when powered at 6V. But the 40109 is a much better solution for levelshifting up. Actually I have a spare 40109 on the breadboard ready for testing.