Relay Switching queries

[Edd]

Hi all,

I'm planning to build a true bypass remote switching system (based upon Geofex.com's schematic - except hopefully without the jfets and just standard relays+stomp switches)

For the gain stages I'm using 4 loops, and at the moment - from the original schematic - that would mean having to press one off and then the one on. I.e. switching the overdrive off, then switching the distortion on - 2 stomps.
What I'd like to achieve is for each switch to turn off the others and turn on itself.

So for example.
With loop 1 on.
Press loop 4
loop 1 turns off. loop 4 opens.

Press loop 4
Loop 4 turns off (no loops on)

Is this possible?
I'm sorry for throwing such a huge question out there, but I can't find any info on it!
Any help would be greatly appreciated!
Thank you
Edd

[R.G.]

I'm planning to build a true bypass remote switching system (based upon Geofex.com's schematic - except hopefully without the jfets and just standard relays+stomp switches)

For the gain stages I'm using 4 loops, and at the moment - from the original schematic - that would mean having to press one off and then the one on. I.e. switching the overdrive off, then switching the distortion on - 2 stomps.
What I'd like to achieve is for each switch to turn off the others and turn on itself.

Is this possible?

No. To do that without the electronics, you need special mechanical switches which mechanically turn off the other switches when they latch in. There used to be mechanical switch setups which did this; they were used in pushbutton car radio station selectors. They probably are no longer available commercially, but you might cannibalize one from a (very) old car radio. That would not help much, because they are not suitable for stomping. So no, you can't do it with just standard relays and stomp switches.

Now that I typed all that in, yes, there is a way to do it. There is a very old trick with relay logic that can do it. But it's tricky to set up and get working. It relies on the fact that a relay's pull-in current is much greater than its hold-in current. You feed a number of relays with a current limited power supply that lets in holding current but not pull-in current to each relay. I have a vague memory of needing an extra contact on each relay for a latching hold in, but can't quite remember how that works. Anyway, the stomp switches are momentary. When you stomp on them, they route pull-in current to the relay for that switch, and it then grabs all the hold-in current, starving the others. They drop out, leaving only the one relay held in.

This is a PITA of special cases and tinkering to get to work. It's far easier to use the single IC one-of-eight CMOS switching setup I put in my article on switching systems. Those cost about $1.00 a chip. Far simpler and cheaper to get running than relays, because you can build the whole mess with no relays at all, just getting the chip to switch correctly with LEDs, and only when it's running hook up the relays.

[Edd]

Use the single IC one-of-eight CMOS switching setup I put in my article on switching systems. Those cost about $1.00 a chip. Far simpler and cheaper to get running than relays, because you can build the whole mess with no relays at all, just getting the chip to switch correctly with LEDs, and only when it's running hook up the relays.

Now my issue is learning/understanding how those CMOS chips work!
I imagine they're equally as cheap in the UK.

To use the LED only approach, would I end up having a switch on one side of the CMOS, with the LED+Resistor on the other?
Then presumably - from what I do 'know' about them - switching the the switch would invert the LEDs power, and turn it on?

Thank you for the reply, very much appreciated!

[PRR]

> they were used in pushbutton car radio station selectors

Those were not electrical switches. They were mechanical clutches which rocked the tuning capacitor or, more often, coil tuning slugs. Wonderful contraptions. Worth trying to find a 1961 Buick radio in a barn-sale, just to refresh our memory.

I'm not sure if this mechanism is/was as common on Edd's side of the pond.

The type of 1-of switch you mean was common on audio gear and sometimes dishwahers etc. And as you say, even a small cat would not be able to foot-stomp one while playing. The semi-affordable ones would easily go into 2 or more states at once, or none at all.

Yes, it can be done with relays. My head hurts thinking about it.

> understanding how those CMOS chips work!

What understand? There's old engineers from the 1970s who HAD to wire this stuff to have any fun (or pay) at all. Connect the dots.

> I imagine they're equally as cheap in the UK.

A) It's a global economy. Prices are the same everywhere.

B) CMOS is probably a penny cheaper in the UK than the US this year. Our internal economy is saggy but seems OK until I shop in the UK and convert to US $.... ouch! I think our currency printing-press is working overtimes so we *think* we have money, and your bankers are more cautious.

[Edd]

Thanks, I'll have a play with the chips mentioned in the schematics and see what happens (hopefully the right thing!)

I'm also considering putting relays in my guitar - to cut down the signal chain just like in pedalboards - so by the end I should be an expert on relays and CMOS!

[R.G.]

> they were used in pushbutton car radio station selectors

Those were not electrical switches. They were mechanical clutches which rocked the tuning capacitor or, more often, coil tuning slugs. Wonderful contraptions. Worth trying to find a 1961 Buick radio in a barn-sale, just to refresh our memory.

Actually, even though the car-radio things may not have been electrical switches, the electrical switch mechanism did exist. I bought one from a GC products supplier back in the mid 70s for a source selector for a preamp I was building. There was a rack of switches and buttons, and pressing a button mechanically unlatched them all, but locally latched just that one switch.

Oddly, it's the exact mechanical analog of what the CMOS 74C373 circuit does - each input tells all the others "reset" while telling its one switch "no, you stay set just a little longer".

The type of 1-of switch you mean was common on audio gear and sometimes dishwahers etc. And as you say, even a small cat would not be able to foot-stomp one while playing. The semi-affordable ones would easily go into 2 or more states at once, or none at all.

That must be what I was thinking of. I never actually hacked the inside of a car radio. Lost youth and all that, I guess.

Yes, it can be done with relays. My head hurts thinking about it.

The only reason I know that is that a friend who worked in the RCA broadcast division's video tape recording design section (this is obviously back while there was still an RCA that was something other than a trademark) told me about it as an alternate to finding and buying the mechanical-latch one-of-N switch from above. It does work. And it *is* a headache.

[PRR]

> each input tells all the others "reset" while telling its one switch "no, you stay set just a little longer".

Global Reset is AND-ed with NOT-Pushed. Mechanical motion/slop keeps the Pushed signal active after reset drops.

> I never actually hacked the inside of a car radio. Lost youth....

You'd love it. Mechanical contraption, low cost, good precision. If I find one for negligible cost, I'll think of you.

> what I was thinking of.

Newark 1981:


Still available:
MULTI-STATION, 4, DPDT
http://www.switchcraft.com/productsummary.aspx?Parent=451
$19 at Newark, 80 in stock
Full Switchcraft product data (Warning! 32MB PDF file!) Multi-switches start near page 300.

Fairly rugged in finger-bashed use. Not stompable.


While finding that, I found this. Off-topic, but I want to use it before I lose it.

Loading for 4.5V-12V amplifiers. You can compute this, but it is a mess of pi and factor-of-2 errors.

[Edd]

Sorry for bumping this =D
RG is there any info available on the type of relays I should use? - I've finally gotten my guitar finished, hence the move back to effects and the post bump -
I've found a list of 12V relays, although I'm not sure of which contact rating to use? Suggestions would be incredibly useful!
I hope to build a demo circuit in the next month =)
Edd

[R.G.]

Sorry for bumping this =D
RG is there any info available on the type of relays I should use? - I've finally gotten my guitar finished, hence the move back to effects and the post bump -
I've found a list of 12V relays, although I'm not sure of which contact rating to use? Suggestions would be incredibly useful!
I hope to build a demo circuit in the next month =)
Edd

You want relays which specifically say "low signal" or "dry circuit" in their contact ratings. This means the contacts make without high voltages and currents to clean off any crud that gets onto the contacts. Low coil power is good. 9Vdc coil rating is also very good for compatibility in a pedalboard environment. I like the NEC series of TQ... relays. Mouser stocks them in 9V now. Other companies make similar stuff: Panasonic, Omron, etc.

[amptramp]

> they were used in pushbutton car radio station selectors

Those were not electrical switches. They were mechanical clutches which rocked the tuning capacitor or, more often, coil tuning slugs. Wonderful contraptions. Worth trying to find a 1961 Buick radio in a barn-sale, just to refresh our memory.

Have you been sneaking around my house?  I picked up a 1961 Buick radio last year at a garage sale, largely because it used the 12-volt plate voltage series of tubes and I wanted to see how well that worked.  A long time ago, I had a Philco-Ford radio that used electrical switching where you could take the chromed caps off the switches and tune the coil that was underneath the cap to set the station frequency.  As I recall, the ones on the left only tuned the low end of the band and the ones on the right only tuned the high end.  This one had the mechanism where pushing one switch let the others pop out.

[PRR]

> Have you been sneaking around my house?

I forgot my camera. Are you able to take a good picture of the 1950s-1960s Delco/Autolite button-tuning mechanism? What R.G. really should see is a movie taken with a micro-lens.... it's a real contraption and some bits are tiny.

It's actually not a "reset all" logic. The button-plate pushes the rocker-link to the desired angle (tuning). You go through all in-between stations (all, not just set stations). You have to bottom-out or it won't quite get-there. And the selected button does not stay-down (you knew where you were by the 600-1600 scale).

> take the chromed caps off the switches and tune the coil that was underneath the cap

Yes, common enough on older parlor radios and obviously useful in a car, without mechanical contraption. This could be adapted to one-of-several audio switching.

> there is a way to do it. .... But it's tricky.... You feed a number of relays with a current limited power supply

Elaborated article, though still unclear, and surely tricky.

(Click for 74KB GIF)