A Switching Scheme

Post by **bubstance** » 18 May 2012, 22:36

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

**EDIT** I think the numbering on the relay is bunged up, but the concept is there.

jimosity · Post by **jimosity** » 19 May 2012, 16:03

I'm also interested in a version that uses a momentary switch.
Specifically a layout of some sort (PCB, perf) or a schematic is cool too.

Post by **bubstance** » 19 May 2012, 21:06

The one above is for a momentary.

jimosity · Post by **jimosity** » 20 May 2012, 16:30

Pinout on the AL5WNK should be:
1= + POSITIVE
2= NC1 (SEND)
3= COMMON1 (SEND)
4= NO1 (SEND)
5= NOT USED
6= NOT USED
7= NO2 (RETURN)
8= COMMON2 (RETURN)
9= NC2 (RETURN)
10= GND

I just made a custom library/part for Eagle, but I can't figure out how to move the name placement on the pinouts in the symbol view.
I tried leaving it as is with overlapping names on the symbol view; then though I could smash it in schematic view to move the pin names around, but that doesn't work.
Any ideas on how to do that? I'll then share the library for the part to make it easier for us.

Post by **bubstance** » 20 May 2012, 18:23

As far as I know the names of pins are fixed and cannot be moved.

jimosity · Post by **jimosity** » 23 May 2012, 00:24

bubstance wrote:As far as I know the names of pins are fixed and cannot be moved.

This is what I'm talking about -- see how the names overlap...I can't figure out how to move those names apart a bit so they are legible.

In Symbol View
http://bandslink.com/share/cap1.JPG

And when you put it in a schematic
http://bandslink.com/share/cap2.JPG

Post by **bubstance** » 23 May 2012, 01:28

Yeah, like I said, I don't think those names can be moved unless you increase the width of the part. I made my relay symbol differently; it makes a bit more sense in my head than an 8 pin device and shows what's happening in the relay. Just use a relay symbol, like below, and then add in symbols for the switches to make a three part element. Then you can arrange it like above and keep the relay symbol separate from the switching elements.

If you want, of course.

rasta_maleek · Post by **rasta_maleek** » 02 Jul 2012, 12:31

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

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 47µF to 100µF, 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.

Relay_Board_Vero_Layout.gif
Remember - the relay MUST be a Takamisawa AL5WN-K. Experiment (and a component shortage!) showed that the capacitor can be as small as 10µF (though it will stop working when the battery gets below about 8.5V) - my latest builds have used 47µF 16V tantalum beads (because I've got a boxful of them). I find that I still have plenty of the "Carling" SPDT footswitches that were pulled from old pedals to use up!

hi mictester
what sholud i do to use this circuit with a 5v/6v supply?
thanks a lot, this is a usefull solution to amp switching

adielricci · Post by **adielricci** » 02 Jul 2012, 15:32

Here's my suggestion of an electronic switching scheme, with a simple flip-flop and bipolar transistors as audio switches, instead of FETs. The 2K2 resistor of the LED can be altered to 10K in the case of superbright ones.

http://www.handmades.com.br/forum/index ... 2422;image

It works.

Chugs · Post by **Chugs** » 02 Jul 2012, 17:27

Cool, but the link requires a password.

jonasx26 · Post by **jonasx26** » 02 Jul 2012, 17:32

adielricci wrote:Here's my suggestion of an electronic switching scheme ..

Can't see the schematic..

What are the advantages of using BJTs instead of FETs?
Seems to me that BJT switching would require very precise DC conditions and source/load-impedances to work properly.

adielricci · Post by **adielricci** » 02 Jul 2012, 21:39

Sorry, I thought the link was open. The reason for using regular bipolar transistors was that FETs were not available easily in my country, and they were extremely sensitive to damage, not to mention much more expensive, at the time I designed this circuit, circa 1987.

https://img225.imageshack.us/img225/614 ... dielmo.png

mictester · Post by **mictester** » 02 Jul 2012, 23:00

rasta_maleek wrote: hi mictester
what should i do to use this circuit with a 5v/6v supply?
thanks a lot, this is a usefull solution to amp switching

Unfortunately you'll need 9V to make the circuit work - it'll work down to about 7.5V but no lower. You'll also have to increase the series capacitor slightly for reliable operation with lowered voltage.

Generating higher voltages from lower voltages is actually quite easy if you use simple switched-mode supply circuits.

jonasx26 · Post by **jonasx26** » 02 Jul 2012, 23:48

Wow. That circuit could use some improvements..

adielricci · Post by **adielricci** » 03 Jul 2012, 00:21

jonasx26 wrote:Wow. That circuit could use some improvements..

Be my guest!

It is the first idea, it worked fine, but I could polarize the transistors with a cleaner source, like a resistive divider with a capacitor, or something along that line.

My intention was to make it as simple as I could, keeping its functionality. Nowadays I prefer to use a 3PDT in my pedals, though.

jonasx26 · Post by **jonasx26** » 03 Jul 2012, 01:23

I'd use op amp voltage followers and CMOS transmission gates in "current mode".

Check out 'Self on Audio' by Douglas Self. It has a great chapter on switching with FETs and CMOS muxes.
Solid state switching can be VERY good when done properly. Sadly, it rarely is. (in the world of stompboxes)

adielricci · Post by **adielricci** » 03 Jul 2012, 11:23

jonasx26 wrote:I'd use op amp voltage followers and CMOS transmission gates in "current mode".

Check out 'Self on Audio' by Douglas Self. It has a great chapter on switching with FETs and CMOS muxes.
Solid state switching can be VERY good when done properly. Sadly, it rarely is. (in the world of stompboxes)

In which case, simplicity goes down the drain. Thank you for the tips, anyway. My proposal dies here.

Post by **The G** » 03 Jul 2012, 14:23

jimosity wrote:[...]
I just made a custom library/part for Eagle, but I can't figure out how to move the name placement on the pinouts in the symbol view.
I tried leaving it as is with overlapping names on the symbol view; then though I could smash it in schematic view to move the pin names around, but that doesn't work.
Any ideas on how to do that? I'll then share the library for the part to make it easier for us.

If you change the visibility from "both" or "pin" to "pad" it'll look like the left symbol:

: Symbols; relay.png (2.44 KiB) Viewed 5437 times

Still, the block variant is not intuitive or easy to use.

You have a custom Eagle library attached, containing both variants. I used the datasheet, but mistakes are still possible. So check it before use.

Emanuele II · Post by **Emanuele II** » 21 Jul 2012, 13:50

my eagle can't load that library..do you have any idea of why it does that??

deafbutpicky · Post by **deafbutpicky** » 16 Oct 2012, 18:28

I made some vero layouts for the momentary- and on/off foot-switch schematics, with the fx-in
grounded while in off state, as mandatory for some higain circuits.
Sorry for the kind of crosslinking, this isn't my "main forum", and musikding is where I keep all my stuff.

http://forum.musikding.de/cpg/displayim ... at=0&pos=0
http://forum.musikding.de/cpg/displayim ... at=0&pos=1

A Switching Scheme [documentation]