(Fixxed) Kemet EA2-5SNJ relay

[Crispy]

I bought my first relay and a momentary foot switch and was wondering if i would be able to get it to work with out the microcontroller IC . i was thinking i could make some kind of flip flop with transistors to change the polarity through my relay coil and toggle that with my momentary foot switch but i have no idea how to do that. i was hoping someone might be able to point me to a schematic i can study or if i will in fact need the microcontroller IC/ PCB. thank you for any advice on this topic.

 

[Robert]

There's a schematic in the PDF for the latching version of the Basic Relay Bypass.

https://docs.pedalpcb.com/project/LatchingRelayBypass-PedalPCB.pdf

 

[Crispy]

Thank you for the link, i think i just do not understand that schematic how it changes the polarity to the coil, it looks like ground is fixed . im thinking i should just get the PCB and do it right .

 

[Robert]

A PCB would be much easier, but here's how it works.

Q2 and Q3 form a push-pull amplifier, they can source or sink current through C3 and the relay coil.

We'll assume C3 is completely discharged.


To latch the relay Q2 applies 9V to C3, which begins to charge.
As C3 charges up the current through the capacitor also flows through the relay coil. This burst of energy latches the relay.
Once C3 is completely charged up to VCC current flow stops and C3 remains charged up to 9V.





To unlatch the relay Q3 grounds the positive end of C3, which is still charged up to 9V from the latch cycle. The stored charge in C3 causes current to flow the opposite direction through the relay coil, unlatching the relay. Once C3 is fully discharged current flow stops, and now the circuit is back where we started... ready to latch again.

 

[Crispy]

thank you so much for taking the time to write all that out. that makes it completely clear how it works. that is really clever how C3 makes it all work like it does.

 

[jubal81]

Win for the search function.
I was looking at that schematic today and wondering about this setup, since my first thought would have been tying pin 10 of the relay to V/2 and roll without the capacitor.

 

[Robert]

The cool thing about this setup is you can jump the capacitor and use a non-latching relay in the same circuit.

You can also put a resistor across the capacitor and reduce the current consumption of a non-latching relay.