Hello,
I have a recording/playback module hooked up to a switch which closes the circuit for the playback button. However the switch I'm using (actually an infrared beam device) closes the circuit too long (about three seconds) which puts the recording/playback module into record mode instead of playback mode. (The circuit needs to be closed for no more than one second.)

I was wondering if I could use a capacitor in series with my switch to "pulse" the voltage which triggers the playback (4.7 volts). However, I don't want to increase the voltage, or do anything else which might damage the circuit. I just want to shorten the time that the circuit is closed.

Could a capacitor be used to control this length of time? If a capacitor could be used to do this, what value would be needed (the voltage measured across the switch is 4.7vdc)?

Thanks,
Zach

PS. I'd also like to know the formula used to figure the proper capacitance so I can understand the logic behind it.

 

Hello,

Perhaps you can use a differentiator circuit.
http://www.interq.or.jp/japan/se-inoue/e_ckt1.htm
You can place a diode (anode to ground) across the resistor to cut back the negative going pulse.

This link comes from the EDUCYPEDIA page on RC and RL circuits.
http://www.educypedia.be/electronics/analogrc.htm

Greetings,
Bertus