Relay Bypass for Stereo Pedals

[bree9217]

Hi! Long time lurker, first time posting to a forum so forgive me for any ignorance.

I'm trying to figure out if I can use one PIC12F675 microcontroller, one SPST soft click footswitch and two relays to switch on and off a stereo pedal. I did several searches on here and google and couldn't find something that worked.

I've been using the code and layout from Coda Effects for mono relay switching.
https://www.coda-effects.com/2016/04/relay-bypass-conception-and-relay.html

I have it breadboarded and I've tried wiring the relays in parallel as well as adding transistor relay drivers from the microcontroller to both relays. Still I only get one relay to switch or neither.

So I guess my question is, can this circuit be modified to activate two relays or does the microcontroller need to be reprogrammed to do so?
Thanks!

[iainpunk]

dude, welcome to the forum

it depends on the particular type of relais you use, i find it odd that the relais is connected to the PIC, so maybe it will supply enough current to active both coils.
otherwise, you'd have to employ the help of transistors to supply the current needed.
if you use both coils in parallel, you don't need to add another diode, the current will only flow through one anyways.

cheers, Iain

[bree9217]

Thanks for the response!
The PIC works well enough for one relay just fine but not two in parallel. I've tried using transistor relay drivers to get it to work and it still only activates one relay. I'm not sure if I'm wiring the drivers up correctly though, as I don't know much about them

[iainpunk]

the coil is connected to GP4 and GP5, what are the voltages on the pins in both the 'on' and 'off' state?
this determines if NPN or PNP transistors should be used.
remember that the coils should be parallel, not series. (its a common mistake i see often on various forums)

cheers, Iain

[bree9217]

the voltages with just one relay wired up like the schematic
GP4
off-4.934   on-4.521
GP5
off-4.933   on-1.208

[bree9217]

and with one driver and one relay, it works just fine. When I add a second driver and relay, the second one won't activate

[iainpunk]

take the coils off of GP4 and implement this schematic, most small transisors will work for this kind of Relay, 2N3906, BC557, AC128* etc...

cheers, Iain

* don't use an AC128, it will work, but its wasted on this since a cheapo transistor works as well, better used in a fuzz pedal

[bree9217]

I'm still having no luck. I used a 3906 and tried with one relay and two in parallel and neither worked. I tried with two separate drivers as well. I was able to get one driver/relay to work when I used an NPN 3904 previously but when I added a second driver/relay, it didn't work. Might try again tomorrow with fresh eyes

[bree9217]

fresh eyes helped! My dumb self had misplaced a ground connection it works perfectly now! Thank you for all your help!

[iainpunk]

nice!
glad i could help

cheers, Iain