A simple Relay Bypass

[owlexifry]

LCSC has suitable relays for cheap as chips and good shipping. If you're doing more than a couple relays, then having a vero may end up being a tedious, repetitive process for what is essentially a modular part. I just had 30 made with all the components on SMD except the relay for a buck a piece. With relay, it would have been ~$2.20 each (I just have an inventory of relays to use). That's not such a bad price if you build a lot of pedals.

i’m probably only going to do like x3 max. i don’t do heaps of builds.
just wanted to whip up those few on vero.

If you’re using a 9v relay, you don’t need to drop voltage/current, so you’d just use a jumper.

thanks for the tip

That relay is not the size you think it is. Take another look at the datasheet.

is this not the same spacing as in my layout?

 

[Chuck D. Bones]

Nevermind...

I was looking at the first Tayda link. Watch out for the height on the one you picked.

 

[owlexifry]

so when i first fired up the circuit it was immediately apparent that my layout (above) had the bypass/active routing backwards (LED on in bypass).

revised layout (for 12V circuit, 520R/9V coil):


verified

fitted it to a CE-2 build running @ 12V. was quite a squeeze.
but it works!
it's an awesome switch. i love it.
thanks for sharing this circuit @Chuck D. Bones

 

[Chuck D. Bones]

You are very welcome.

 

[Big Monk]

@Chuck D. Bones

I'm working up the design for the Forum Monk Vibe in the big enclosure.

Can this bypass be configured to switch a Bi-Color LED?

 

[Chuck D. Bones]

How many leads on the LED?

 

[Big Monk]

How many leads on the LED?

Common Anode likely, so 3, with 2 cathode leads.

 

[Chuck D. Bones]

If your plan is to have the LED glow one color when the relay is engaged and another color when the relay is disengaged, I can think of two ways to do it.
1. Add a transistor and two resistors to drive one of the LEDs to the opposite state of the other one.
2. Illuminate one of the LEDs constantly. A Red/Green LED will glow Red/Yellow or Green/Yellow, depending on which LED is on constantly.

If you had a 2-lead bidirectional LED, then there is another option.

 

[Big Monk]

If your plan is to have the LED glow one color when the relay is engaged and another color when the relay is disengaged, I can think of two ways to do it.
1. Add a transistor and two resistors to drive one of the LEDs to the opposite state of the other one.
2. Illuminate one of the LEDs constantly. A Red/Green LED will glow Red/Yellow or Green/Yellow, depending on which LED is on constantly.

If you had a 2-lead bidirectional LED, then there is another option.

How would #1 integrate into your existing simple bypass?

 

[Brett]

How would #1 integrate into your existing simple bypass?

Unverified, but maybe something like this would work for your application:

*Updated drawing per @Chuck D. Bones suggestion in post #113 below.

 

[Big Monk]

Unverified, but maybe something like this would work for your application:
View attachment 58663

Nailed it. That was @Chuck D. Bones solution as well.

 

[Big Monk]

Quick question as I try and do some design work for the Forum Univibe:

If I were to use more than one DPDT relay for the Speed switching, am I correct in this assumption:

If I place two relay coils in parallel, would I use their parallel resistances in the coil resistance calc to get my proper coil resistor?

 

[Chuck D. Bones]

Unverified, but maybe something like this would work for your application:

Wow, great minds. That gate stopper resistor (RX5) should be larger to guarantee it does the job. I like 10K for that.

 

[Chuck D. Bones]

Quick question as I try and do some design work for the Forum Univibe:

If I were to use more than one DPDT relay for the Speed switching, am I correct in this assumption:

If I place two relay coils in parallel, would I use their parallel resistances in the coil resistance calc to get my proper coil resistor?

Yes, but the 555 does not have infinite drive capability. When powered by 9V, we cannot expect the 555 to sink more than 30mA. If the sum of the coil currents exceed that, then you need a MOSFET to drive the coils. This is an example "requirements creep" where a circuit works fine until someone changes the requirements.

 

[Big Monk]

Yes, but the 555 does not have infinite drive capability. When powered by 9V, we cannot expect the 555 to sink more than 30mA. If the sum of the coil currents exceed that, then you need a MOSFET to drive the coils.

The more I think about it, standard switching may be the best bet if this is going to be a forum build.

 

[Brett]

...That gate stopper resistor (RX5) should be larger...I like 10K for that.

I figured the values may need to be adjusted some, but thank you for confirming! I've updated my post above for posterity.

 

[Paul.Ruby]

This is just FYI. I made a discrete soft-touch toggle circuit for my TPA3118 power amp pedals that would also work for all this stuff, if anyone want such a thing. This link jumps to the post about it in the TPA3118 amp thread.

TPA3118 60W Power Amp Module

EDIT #2: I've decided this is not worth the effort. The only way to really avoid pop is with proper behavior. Don't plug in a speaker cab until everything is powered. Unplug speaker cab first for power down. A mute button or stand-by on the amp might be a nice-to-have, but still requires proper...

forum.pedalpcb.com

 

[Brett]

This is just FYI. I made a discrete soft-touch toggle circuit for my TPA3118 power amp pedals that would also work for all this stuff, if anyone want such a thing. This link jumps to the post about it in the TPA3118 amp thread.

TPA3118 60W Power Amp Module

EDIT #2: I've decided this is not worth the effort. The only way to really avoid pop is with proper behavior. Don't plug in a speaker cab until everything is powered. Unplug speaker cab first for power down. A mute button or stand-by on the amp might be a nice-to-have, but still requires proper...

forum.pedalpcb.com

This is cool. You may want to consider posting a new thread for this since it’s not really related to this circuit.

 

[sammo303]

I have a few questions that I haven't seen on this thread. Apologies if I'm covering old ground.

- Looking through relay datasheets it seems like current draw reduces with increasing coil voltage, which is to be expected. Given the current passes through the 555 which can't tolerate too much, is there any downside to simply using a relay with a 9v coil to remove R4 and minimise current draw?
- If we use a latching relay instead, besides other modifications, would I be right in thinking the limit on current through the 555 could be increased due to the short duration during state change? If so, perhaps a simple circuit could still be used to drive more than one relay if that was ever needed.
- Any idea what modifications would be required to make the circuit work with a latching relay? Pedalpcb's basic relay switching schematic is a fair bit more complicated for the latching relay option so I suspect modifications will end up sacrificing the simplicity but keen to hear if anyone thinks a similarly bare bones schematic may work.

Thanks,
Sam

 

[Chuck D. Bones]

Yes
No
More mods than are practical IMHO. Without getting into the gory details, if you want to reliably drive a latching relay, use a microcontroller.