Replacing a pushbutton with circuitry

Thread Starter

yardleydobon

Joined Apr 19, 2009
19
I'm hacking an mp3 player that has a pushbutton switch. The input pin of the chip
that senses button presses is normally pulled up to 3V. When the tactile button
is pressed the pin gets shorted to ground. I want to replace the mechanical action
of pressing a button with a signal from another circuit.

My control line switches from floating to ground when the event of interest
occurs. How can I make the mp3 player interpret this signal as a button press?

Is a capacitor between the input pin and the control line good enough?
Or would it be better to use a pnp in parallel with the pushbutton with control
line going to the base?
 

Thread Starter

yardleydobon

Joined Apr 19, 2009
19
Well it's obvious when you say it like that!:D

The grounds are in common.
I'm sorry I should have been more specific. The pushbutton only momentarily
brings the input pin to ground, but the control signal _stays_ at ground for a long
while. So I need to pulse the pin to ground.

I can think of two ways to do this:
A capacitor between the input pin and control line would act as a temporary short
bringing the pin to ground. I think I need a large resistor going directly
to ground to drain the capacitor too.

An RC circuit that pulses the base of a transistor driving it to saturation temporarily
might also work. I think using a FET would be better though.

It's a pretty simple problem that I'm sure has been solved thousands of times by
people hacking off the shelf gadgets with pushbuttons, but I couldn't find the answer
with google or in the forums. I just want somebody to tell me the "right" answer.
 
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