Re: Mictester's CMOS Relay Bypass Module

Posted by Freppo on
URL: http://guitar-fx-layouts.238.s1.nabble.com/Mictester-s-CMOS-Relay-Bypass-Module-tp19021p45383.html

purity wrote

Thanks for the addition Freppo.
Am I wrong in stating that a flyback diode as youve described is not desired for this latching relay as the current to trigger the relay must flow both ways (or actually the flyback voktage should be blocked both ways)? Two zeners rated at 5.1V with the anodes tied together, and the cathodes across the coil are more (?) suitable for this application.

Also, the transistor part is to convert the constant high / low output of the inverters to a single bidirectional pulse towards the relay coil, which only needs a pulse and not a constant current. Minute current consumption is the design idea here in case you dont know the reasoning behind this circuit. Your alternative could use a more common and cheaper nonlatching relay though.

I didn't know that this layout was for a latching relay. In that case you are right. My bad. :)
Two zeners would be the way to go for overvoltage protection (which the schematic lacks).
My version (which I have used alot with good results) uses a common nonlatching relay.

Aha, I see the point of the transistor section now. However, it would be possible to omit a few components and shrink the layout a bit by using a pair of the unused inverters as the edge to pulse converters insted of the additional transistors, and C1 and R1 are still not needed for the flip flop.