Jason White wrote:

> Hello All. I'm currently working on a project that requires me to use
> 2 1:16 multiplexers to interface with various peripherals due to
> limited I/O. I'm curious how much (RC?) filtering would be required to
> make a short fast pulse (eg. 1-10khz 1-5% duty cycle) a suitable
> signal to drive a relay.
>=20
> Thanks
>=20
> relay: odd Chinese 20A H-Bridge relay on hooked up via opto-coupler,
> No other specs
> multiplexers: CD74HC4067M
> MCU - 16f690

Use a diode plus capacitor to create a peak detector. Use a FET as=20
switch to the opto. Resistor to ground determines time before FET turns=20
off. High impedance of gate lets you use small cap values.
It WILL have a slow turn off which may cook the opto.
In which case use a 74HC14 schmitt trigger to square it up (no FET=20
needed). (available as a single channel SMT part SN74LVC1G17DCKR & similar)

Or use something like a 74HC123 retriggerable monostable with a timeout=20
longer than your refresh rate. (also available as a single channel SMT=20
part).

Robert


--=20
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