Thanks to the both of you!
I'm glad no one had any complaints about the BC550.
seems a little complex
Yes. Should have noted that relay / zener pulldown was sourced from 70's console and meant for simple switches. I think its complexity had to do with PSU stabilization? Circuit draws more current while unselected than selected.
add would be a small series resistor before the 10uF cap that decouples the incoming supply to slow up its recharge current
Unfortunately there's no going back at this point; those little relay sub assemblies are already in place in the hundreds. May I ask, why slow the recharging, potential noise?
Use internal pullup of the controller.
Yeah, after some reading, found a suggested minimum 1k pulldown was needed to produce .5mA, the minimum current required for button contacts to self clean. Perhaps the button was built to do this mechanically, but playing it safe. Was this bad information?
- Dampening a digital output is unnecessary.
Playing with this was fun. Cap is just precautionary. I found that when base of BC550 was left floating, my hand acted like a touch sensor and put it into oscillation, as well if M/C ground and PSU ground lose reference. Cap acts like a sort-of schmitt should anything get accidently disconnected (I had this image of a session getting ruined because my desk was buzzing).
You only need one resistor in series with the LED.
Yessr, thank you. Only did it this way so each mc pin has current protection, which is probably redundant as protection is likely on-chip as well.
One diode should be enough if they don't sit a meter apart.
Good to know! But too late to change.
