Request: Latching relay switching circuit

Want to replace that regular 3PDT stomp switch with one of those nice “soft-touch” momentary switches? Here’s a vero layout for a latching relay circuit based on a schematic by R.G.Keen. This particular layout works with the dual coil latching relay from smallbear (NEC EA2-5TNJ) which is the one I used. Other relays may or may not work; have a look at the datasheet for the NEC and compare.

And here’s a picture of my finished circuit. Works like a charm.

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14 thoughts on “Request: Latching relay switching circuit

  1. Ooh… i found the correct name of the needed switch arrangement: S-R latch (with two individual momentary contacts, one for “Set” and one for “Reset”)

  2. Hey Harald, im slowly working on the “programmable switcher” idea… I´ve found that we need a kind of switching that have individual inputs for ON and OFF states. With a single latch control, we dont be able to “select” the state with the dips… this configuration will only alter the previous state. Maybe the same design configured to perform a “OR” gate will work… not sure.

  3. That is actually quite an intriguing idea. Afraid I don’t have much time these days either, but I’ll definitely keep it in mind. Do let us know if you end up making it 🙂

  4. There’s not enough room on the board as it is so you’d most likely have to tack on a tiny additional board with just the 78L05 and 2x caps of decent size (47uF maybe). You need three strips, “input” at +9v, ground at center and “output” gives you +5v. Caps go from either +v side towards center and ground.

  5. “I guess when using a TQ2-L-5V it doesn’t hurt to add a 78L05 and a couple of caps, right?”

    So how exactly would you wire that ^ up?

  6. Right, without knowing much about that particular relay I’d say that’s a good idea. You don’t want to exceed the voltage limit.

  7. I guess when using a TQ2-L-5V it doesn’t hurt to add a 78L05 and a couple of caps, right?

  8. Hi Jimmy,
    Yes you wire it up like you would a regular DPDT mechanical switch using the “SW 1” – “SW 6” in place of the switch lugs. And no, you won’t be able to use a bi-colored LED with this circuit I’m afraid.

  9. This is awesome – thank you so much for your postings – I’m looking forward to trying out some pedal builds! I’ve put these circuits together to build a quiet bypass looper – I was wondering do I wire the board up as if I was wiring up a standard dpdt mech. switch? I was also wondering if there was a way to use this setup with a bicolored led (for an ab box?) prob not possible with current layout – but is this a possibility for the future?
    Great work!

  10. I don’t think that relay will work, sorry. It’s a single-coil and you need a double coil. I had a look at the other relays they had and I couldn’t see any that would fit (do keep in mind I’m not an expert at this).
    Here’s a link to the one I used:
    If you look at the data sheet for the NEC-ea2 you’ll see what the double-coil one looks like.

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