A Switching Scheme

jubal81 · Post by **jubal81** » 19 Feb 2013, 03:05

Just thinking - is there a way to wire this up so that pressing one button sends an 'off' signal to the other? That way only one effect will be active at a time.

Damn, I really need to learn how to program ...

mictester · Post by **mictester** » 19 Feb 2013, 06:54

jubal81 wrote:Just thinking - is there a way to wire this up so that pressing one button sends an 'off' signal to the other? That way only one effect will be active at a time.

Damn, I really need to learn how to program ...

Don't bother with programming - take a look at a 4013 dual bistable. It'll do what you want!

xbobbytherookiex · Post by **xbobbytherookiex** » 22 Feb 2013, 11:04

I was wondering if somebody could make a pdf file for a board that can be used with momentary switches shown in this post or a vero layout
https://www.freestompboxes.org/viewtopic ... &start=120
Please can you write values and components used, if you have the time? Can Panasonic TQ2-L 5VDC relay be used? I just want to make a true bypass looper with momentary switches cause 3pdt switches keep breaking on me. Sorry for all the questions, I am an amature builder. Thanks in advance.

mmolteratx · Post by **mmolteratx** » 12 Mar 2013, 20:40

Had some fun and made a template for myself to use with a momentary SPST. Verified it today with a Fuzz Face circuit.

mmolteratx · Post by **mmolteratx** » 13 Mar 2013, 02:12

Hey Mictester, I can't get the relay to actuate with a battery. Reading voltages, my power supply is putting out 9.3V, all of my batteries between 8.6-8.8V. The latch actuates and the LED will light up, but the relay won't switch. Are the battery voltages just too low?

mictester · Post by **mictester** » 13 Mar 2013, 07:52

mmolteratx wrote:Hey Mictester, I can't get the relay to actuate with a battery. Reading voltages, my power supply is putting out 9.3V, all of my batteries between 8.6-8.8V. The latch actuates and the LED will light up, but the relay won't switch. Are the battery voltages just too low?

I can't read the relay part number from your photograph. Are you using the right one? Is the capacitor in series with the relay coil big enough? I usually use 220µ or 100µ (either will work reliably with the specified relay). Please note that this MUST use the single-coil latching version of the relay (not the humbucker version!

)

mmolteratx · Post by **mmolteratx** » 14 Mar 2013, 03:27

mictester wrote:
mmolteratx wrote:Hey Mictester, I can't get the relay to actuate with a battery. Reading voltages, my power supply is putting out 9.3V, all of my batteries between 8.6-8.8V. The latch actuates and the LED will light up, but the relay won't switch. Are the battery voltages just too low?
I can't read the relay part number from your photograph. Are you using the right one? Is the capacitor in series with the relay coil big enough? I usually use 220µ or 100µ (either will work reliably with the specified relay). Please note that this MUST use the single-coil latching version of the relay (not the humbucker version! )

Using a Takamisawa AL5WN-K. Capacitor is 100u. Voltages on the 40106 with a power supply are 7.6-7.8V. Removed the resistor in series with my power supply (47R) and jumpered it, now a battery will work down until ~8.6V.

mictester · Post by **mictester** » 14 Mar 2013, 06:20

What value is the series resistor with your LED? There could be some "current robbing" issue going on. I use 15k or even 18k in series with my LEDs because they are low current / high brightness types and they're visible in daylight even with that kind of value! If you still have issues, please put up the circuit you've used and the board layout - there may be a mistake you've overlooked, and I frequently find that it's a good idea to have another person look over my work - they often find the obvious error that I've missed!

mmolteratx · Post by **mmolteratx** » 14 Mar 2013, 06:35

LED CLR was the problem. Upped it to 15k from 6k8 and now it's working flawlessly down to around 7.5V or so. Need to replace the LEDs with higher brightness ones though.

EDIT: I love this switching scheme though. Switch is $1.50, I bought 1000 relays for $350 and a 40106 is 20¢ in quantity. Other parts are practically free since I've got so many. So a little over $2 for switching now, and I don't have to deal with those piece of shit blue 3PDTs. Dunno if I like it better than triggering a CD4066 with a 40106, but the price I got on the relays made me give it a try, and the fact that it resorts to bypass when power is cut is certainly nice.

jonasx26 · Post by **jonasx26** » 14 Mar 2013, 19:02

mmolteratx wrote:Here's a drop in PCB that uses a momentary switch. Haven't yet built it, but all looks good. 1.1375" x 1.0500".

[ Image ]

.brd - http://dl.dropbox.com/u/8021347/Relay.brd
.sch - http://dl.dropbox.com/u/8021347/Relay.sch

What happens when both inputs and outputs of the inverter is grounded?
Input is at ground > output tries to go high, but it can't.. Draws lots of current, could kill the chip.

mictester · Post by **mictester** » 16 Mar 2013, 01:07

mmolteratx wrote: Dunno if I like it better than triggering a CD4066 with a 40106, but the price I got on the relays made me give it a try, and the fact that it resorts to bypass when power is cut is certainly nice.

I prefer it to the 4066 - we're talking a solid copper path (that's the new "true bypass", by the way). You can connect two relays with the coils in parallel so you can have QPDT switching if you want (for stereo effects). I've also used the extra ways to mute high gain circuits more effectively to prevent noise breakthrough in bypass mode. The little relays are not susceptible to static damage (whereas the 4066 can easily be fried), and the current drawn by the whole circuit is negligible - your LED draws much more!
One thing that I've done on recent builds is to add a small value resistor in the positive supply of the transistor part of the switch (I use 10Ω) just to help prevent switching spikes breaking through into high gain effects.
I've used this switch with wah, fuzz, flange, phase, chorus, echo and all the rest. It started out as a way of using up a drawer full of SPDT Carling switches (that were almost indestructible) that had been removed when doing "true bypass" mods to Cry Baby pedals!

mictester · Post by **mictester** » 16 Mar 2013, 01:23

rasta_maleek wrote:what could i do to use the same relay, but 9v type?

You'd need a higher supply rail. The capacitor just dumps a small current pulse of about ½Vbatt through the relay. To get the ~8V pulse that the nominally 9V relay would need, you're going to have to use a 15V supply.

mictester · Post by **mictester** » 16 Mar 2013, 01:27

bubstance wrote:Just so it's there, here's a combination of mictester's circuit and a debounced bistable flip-flop using a 555.
.

The 555 will draw more current than the whole of the rest of the pedal!

Chugs · Post by **Chugs** » 28 Mar 2013, 20:28

I tried the 40106 with momentary switch version and it works but when power is applied to the pedal the LED will light even though the pedal in bypass. Tapping the switch will turn the LED off and put the bypass mode and led back in sync. Any suggestions to remedy this?

mictester · Post by **mictester** » 29 Mar 2013, 01:31

Draw exactly what you've built - I'll try to help you debug it. On some that I've built, I've had to introduce a simple power-on reset circuit to guarantee that everything is in the correct state.

Chugs · Post by **Chugs** » 29 Mar 2013, 10:34

Thanks. Here is what I built.

MAmstutz · Post by **MAmstutz** » 31 May 2013, 23:40

What an awesome build! Has anyone made a vero layout for a momentary switch? I believe everything I am seeing is SPDT unless I am mistaken...

deafbutpicky · Post by **deafbutpicky** » 01 Jun 2013, 13:08

I posted one a while ago.

adielricci · Post by **adielricci** » 01 Jun 2013, 15:35

Another idea, without relays:

trixdropd · Post by **trixdropd** » 04 Jun 2013, 05:30

mictester wrote:You'll all know my hatred of the crappy TPDT and similar footswitches.

I still have customers who insist on "true bypass" and a "solid copper path bypass". Buffered bypass is almost always better, but just to satisfy these (very wealthy / influential) musicians, I frequently use bistable relays. Many players are deeply distrustful of mains powered effects, and (perversely) demand batteries that last for many hours. I also have a large supply of really sturdy SPDT footswitches (like the old "Carling" ones). To overcome the deficiencies of the switches (they crackle and can't do proper bypass), I've been using the following circuit. The relay is easily available from all the major suppliers (including many Ebay ones) and if used in this circuit, draws micro-amps!

Ultra-low_current_relay.png
The relay is slightly unusual - it has two stable positions, and is set and reset by small current pulses sent in one direction then the other through the coil. The transistors I used in the originals were BC183L for the NPN and BC213L for the PNP. You can also use 2SC1815 and 2SA733 or BC550 and BC560. The last batch of them had blue LEDs wired across the anode of the diode to ground through a 8k2 resistor, and used 2N3703 (PNP) and 2N3706 (NPN), and were made to fit on to the back of the footswitch.

The circuit gives six big advantages:

1. Hermetically sealed gold contacts - clean and quiet switching.
2. Additional relays can be put in parallel with the first one. You might have to increase the 100µF to 220 µF, but the switching will be entirely reliable.
3. Draws minute current - the whole of the battery power will be used to power your effect and the indicator LED!
4. Passes the "disconnected battery" "True Bypass" test.
5. Costs less than a good quality DPDT footswitch.
6. Allows simple connection of an indicator LED.

A couple questions...

How can this circuit be "reversed" in that instead of the ground being the switch, i want the ground always connected and the +v to be my switch, this way I can make a 2 loop box with a trs connector with a common ground. In this current iteration I end up with a common + on the sleeve which is less than ideal. I'd also like the led indicator.

If that can be achieved, how about my "remote" switch having an led as well and being powered only with the 2 switch wires. Can it be done with this setup somehow??

A Switching Scheme [documentation]