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dine1967 8th April 2003 01:45 PM

Momentary relay driving circuit
I bought the following chip from renton which is a preprogrammed PIC and works on sony protocol. I would like to use this for remote control of my preamp (volume up /down). The problem with the chip is that its output is not in pluse mode. ie. if I press the remote , the corresponding output goes from 0 to 1. It stays at 1 till I press the button again. Is there any circuit to drive relays momentarily ie it clicks everytime the output at PIC changes???? thanks

thylantyr 8th April 2003 02:57 PM

Many ways to skin a cat.

Edge triggered "one-shots".

Example; The cmos chip, the 4538 is a monostable multivibrator.
It's edge triggered, either rising or falling edge (you pick).
You select the output pulse duration. Connect the output
to a transistor to drive the relay.

tiroth 8th April 2003 03:19 PM

We need something triggered on both rising AND falling edge though, right? Two ORd 4538s (one rising, one falling) I guess. There has to be a more elegant solution though...

thylantyr 8th April 2003 06:15 PM

You get two one-shots in one IC package, use two
or'ing diodes to drive the relay transistor. Are you looking
for a single transistor solution, something simpler along
those lines?

tiroth 8th April 2003 06:38 PM

Ah...didn't think of that obvious solution. Nice!

dine1967 8th April 2003 06:57 PM

isn't this same as a standard IC555 timer in monostable mode. Iam new to this digital stuff .... please help

thylantyr 8th April 2003 07:44 PM

I think the 555 mono mode only triggers on negative edges.

dine1967 8th April 2003 08:02 PM

thanks, will order the IC and get cracking.

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