[sdiy] gates and clock inputs to a microprocessor

[Jason Proctor]

hey Danjel,

on the Arduino module i used MC34072 comparators with the threshold 
set to 1.2v or thereabouts, on digital inputs and outputs. works 
fine. the opamps are powered from a unipolar supply so there's no 
negative voltage possibility.

someone correct me if i'm wrong here, but the pullups only come into 
play when there's nothing connected to the input. it's to prevent the 
pin from floating, which uprocs don't like. if you have something 
else connected, then its impedance will be much less than the pullup 
value and whatever's the other side of the pullup won't count for 
much.

on the analogue inputs & outputs i used opamps with scaling and 
biasing to convert the Ard's 0-5v voltage range to +/-5v at the 
outside world. this is so that an Ard LFO sketch could have a bipolar 
output, and that bipolar input signals would behave "properly". just 
like an analogue module.

i kinda dropped the ball on my part of getting the Ard circuit and 
board layout together (sorry Byron...) but i hope to have something 
sorted soon. the circuit will go to sdiy for feedback and approval 
before anything goes to fab.

hth
J



>I am working on module where I have a microprocessor receive gate/trig
>inputs for clock and reset controls.
>
>what do I need in terms of analog circuits to condition those inputs?
>e.g.
>-for input over voltage protection would I use a resistor plus 5V zener?
>-comparator to allow low voltage signals trigger?
>-series diode to protect from negative voltage?
>
>Also the uP will be outputting gate signals. Should these be buffered
>or can I just drive straight from the output pins?  (it is an
>atmega168)
>
>Also if the input pins of the microprocess are using pullups, how
>would I have an incoming pulse trigger on rising edge? would I need to
>put it through an inverter?
>
>I am sure all this stuff has been covered and well documented in
>schematics. I am going to head over to MFOS to get some ideas but
>thought it would be good to check some other resources.
>
>
>cheers,
>Danjel
>_______________________________________________
>Synth-diy mailing list
>Synth-diy at dropmix.xs4all.nl
>http://dropmix.xs4all.nl/mailman/listinfo/synth-diy