Simplest relay bypass possible - no microcontroller

spi

Well-known member
I don't see a pad for an LED on these... is there a way to hook one up without having to take up one side of the relay?
The SW pad connects to ground when pedal is on, to control led. You can make little vero board to hold your led and CLR, with power coming from +V and ground going to the SW pad.
 

PedalPCB

Admin (Robert)
Staff member
If you flip the board over and look on the back there are markings for installing an LED directly to the relay bypass PCB.
Omit the transistor that is normally installed in this location. (Q2 on the Latching board)

1619383617280.png

For the Latching PCB R1 becomes the current limiting resistor.
1619383714964.png
 
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PedalPCB

Admin (Robert)
Staff member
Doh, what a mess these two projects have become. :ROFLMAO: :cautious:


It's the second 10K below the 555. (All the way at the bottom)
 

Sage

New member
What happens if power is removed while the pedal is engaged? Will the latching version switch back to bypass to allow signal through?
So I bought several of the latching version of these to try out, and I just finished using one to convert a Boss pedal to true bypass. Some observations:

1. If you remove power while the pedal is engaged, the pedal will remain switched "on," which means you won't be able to switch it back to bypass mode until power is reapplied. Until then it stays engaged, which means it won't allow signal through. If you need the pedal to switch to bypass mode when power is lost, the non-latching version should do that.
2. When power is reapplied, the pedal switches to bypassed mode, regardless of whether it was bypassed before it lost power. So if you lose power while the pedal is engaged, and then power comes back, the pedal will be bypassed.
3. Switching is surprisingly reliable. Debouncing is solid. I haven't been able to trip it up. Holding down the switch does NOT cause the relay to oscillate back and forth, like in some flip-flop driven circuits.

All in all, I'm very impressed with these. The fact that it doesn't require a microcontroller makes it friendlier to DIY than most other latching relay boards I've seen. In fact, this is the only non-microcontrolled latching relay board I'm even aware of. It's my new favorite module for converting Boss and Ibanez pedals to true bypass.
 

equinox

New member
I likewise bought a couple of these also and am AMAZED at how well they work, thank you soo much Buggs!! This is exactly what I was looking for and NO micro controlled and just simple 555 flip-flop circuit.:)

They draw almost no power consumption beyond the LED at like 3mA. I was measuring like 28mA on the non-latching.

Yes, as someone said, if power disconnected, they will revert to Bypass mode, which I prefer, so good with that also and to start out every power up with clean and everything bypassed.

Still waiting on the document release to see how this circuit is working!! When will it and a schematic be available??
 

equinox

New member

Hey PierBit,

NO. A5w-K will NOT work as the circuit and TQ2-L-5V are set up for a "Latching" type of circuit. These relays circuits are either Latching or Non-Latching and again, this is for "Latching" type. Buggs and PedalPCB have another board for non-latching thou. The difference is once triggered, the Latching-type uses very little current, but can cost more. The non-latching is less espensive, but higher current draw!

Takamisawa DOES have "Latching" type relays. but you would need an "AL" in the model not "A", as the "A5w-K" is non-latching type if you look at the datasheet!

I'm still waiting on the Schematic!! :O It's been months and an easy circuit. Not sure what is taking so long, maybe too many other projects, but would suggest FIFO flow, so not working on future ones unless current are closed out. A schematic and documentation release would be greatly appreciated.

p.s. - The board and design works excellent, so much appreciated!
As long as Latching-type and similar pinouts and voltage, you should be able to use in any of the same type of relay.
 

PedalPCB

Admin (Robert)
Staff member
Not sure what is taking so long, maybe too many other projects, but would suggest FIFO flow
Right now I'm prioritizing the projects that can't easily be built without the docs. (Unique drill templates, special wiring diagrams, optional/alternate parts, etc)
 

PierBit

New member
Hey PierBit,

NO. A5w-K will NOT work as the circuit and TQ2-L-5V are set up for a "Latching" type of circuit. These relays circuits are either Latching or Non-Latching and again, this is for "Latching" type. Buggs and PedalPCB have another board for non-latching thou. The difference is once triggered, the Latching-type uses very little current, but can cost more. The non-latching is less espensive, but higher current draw!

Takamisawa DOES have "Latching" type relays. but you would need an "AL" in the model not "A", as the "A5w-K" is non-latching type if you look at the datasheet!

I'm still waiting on the Schematic!! :O It's been months and an easy circuit. Not sure what is taking so long, maybe too many other projects, but would suggest FIFO flow, so not working on future ones unless current are closed out. A schematic and documentation release would be greatly appreciated.

p.s. - The board and design works excellent, so much appreciated!
As long as Latching-type and similar pinouts and voltage, you should be able to use in any of the same type of relay.
Thank you so much
 

equinox

New member
Ok. On vaca from 7/5 until 7/19 and took some time yesterday. I think I have this Simple Relay Bypass Latching design figured out!
I don't know where it originated and the Docs are still outstanding. Buggs can verify this, but I'm 99% certain it's correct.
Again, I've tried about 4 different designs from just using 3904/3906's and NO 555's to using this one, to using one's non-latching and latching and I like this one and it works the very best! So kudo's to Buggs and whoever originated this from. The response and non-triggered switching is again, the best I've tried and I have a use for this, so very important.

Attached is the design I came up with for this, but needs confirmation. Until then....Enjoy! Simple Relay Bypass Latching - Schematic.png
 

equinox

New member
fyi, i did a little test today...checked the current draw difference between Non-Latching and Latching built exactly and with 5mm Red LEDs.
The results were as follows, fyi....

Non-Latching (disengaged) -2mA
Non-Latching (engaged) -34mA
Latching (disengaged) -2mA
Latching (engaged) - 3mA
 

PedalPCB

Admin (Robert)
Staff member
It doesn't feel right calling it an original design since it's such a simple circuit using common topologies, but the Latching circuit isn't really directly copied from any other design. I don't know of any others that are exactly the same.

Using the 555 in monostable mode (as a flip-flop) is a basic task, it's in all the text books and the 555 datasheet. It's been done in quite a few pedals over the years, more recently known as "Incandenza Bypass", but has been much longer than that.

The Latching version builds on that and uses the charging/discharging properties of a relatively high value capacitor. When voltage is first applied to the capacitor a high current will flow as it charges. As the capacitor charges the current will reduce to near zero. This provides the short "positive flowing" current pulse required to latch the relay.

When it's time to unlatch the relay the positive side of the capacitor (which is still fully charged) is pulled to ground, causing current to discharge in the opposite direction. This provides the short "negative flowing" current pulse required to unlatch the relay.

The push-pull amplifier serves two purposes... It takes the load off of the 555 timer, but more importantly it also inverts the state of the flip-flop circuit to ensure the circuit always starts up with the relay disengaged. Without the push-pull the circuit would work, but the power-on state would be unpredictable.


I have a modification for the non-latching version that can bring the engaged current consumption down to around 10mA but haven't had a chance to add it to the PCB yet.
 

slackshampoo

New member
I have a EA2-5TNJ latching relay I was hoping would work. It unfortunately doesn’t appear to. But, I’m also not totally clear on how this should be wired up. Not sure how the sw and gnd pads are supposed to be wired. I saw the earlier post that stated an LED should be hooked up instead of the 3904 transistor above the 555, I’m assuming that means the other pad for the transistor should be left empty?
 

PedalPCB

Admin (Robert)
Staff member
EA2-5TNJ is a dual coil latching relay, you need a single coil latching relay. The Kemet part number for that would be EA2-5SNJ.

If you're using the relay module with a PedalPCB project then the IN/GND/SW/OUT pads are a direct connection to the pads at the bottom of the effect PCB. The relay module will light the LED on the main effects PCB, no substitutions are needed.

The SW and GND pads are used to light the LED on the effect PCB, if you're using a PCB from any other supplier then you might need to install an LED in the place of the 3904 transistor as described above and ignore the SW/GND pads.
 
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