Help with SP3T relay (on-off-on)

Question

I don't really know electronics, so please excuse my lack of probably even basic knowledge

Ive modified a guitar, with SP3T/DP3T switches, which connect guitar pickups in different configurations (series/parallel/combinations/phases etc.). i used Mini toggle switches. everything is passive - no active electronics.

so, i have a new idea to make a 'computer' controlled version of the same thing (maybe with raspberry pi, or something, i did not think about the 'controlling' part yet).

but i need SP3T relays - and here i need help - there is so many types - most of them are industrial stuff, big bulky.

Can you recommend, or guide me to what type of relays i should be looking for? even proper naming for the stuff i'm looking for will help (googling SP3T relay does not help...)

• i think that i need physical connection, not solid state (its just my guess) - i think that i want a good old mechanical connection here because the switches will be connected to a pickup, so sound quality is important, and i guess solid state may harm the quality...
• i definitely need 3 positions - ON-OFF-ON
• i think i want it to be latching (i don't want to keep applying voltage to keep the switch in ON position)
• i believe it better to get some low voltage activated ones (idk - 5 volts or less?) i don't think battery powered controller (whatever it will be) will have enough oomph.

Thanks in advance!

Answer 1

and i guess solid state may harm the quality

Overcome your fixations here. I'm (also) a guitarist (and music producer) and have recorded probably about 100 of my own songs and, it wouldn't bother me one bit to use solid state switching and dump mechanical relays straight into the garbage. I've also mastered about 500 other songs hence, I have some knowledge in this area that is meaningful.

So, forget about mechanical relays (you'd have to use sealed reed relays anyway to avoid contact oxidation issues) and use analogue multiplexers to do the guitar signal routing. Of course, the devil is in the detail and some will work better than others but, given that this question is fairly open-ended, I can only generalize on the technology.

Using analogue switches will mean battery consumption is in the low mA range (as opposed to relays that will have a high tens of mA consumption).

If analogue switch circuits can be engineered to accurately multiplex microvolt level thermocouple sensors into a common amplifier chain then, there's absolutely no reason why the same ideas can't be used for millivolt level signals from guitar pick-ups. It's a no-brainer for me.

Answer 2

I don't think three position relays exist - you'll probably have to use two SPNO or SPDT relays where you are thinking of using a three-position one.

Latching relay do exist. You will probably want the two-coil type - pulse one coil to operate, pulse the other coil to release. With a single-coil latching relay, you apply power in one polarity to latch, opposite polarity to release.

Answer 3

One could choose two logic level reed relays cascaded to make it choose 3 combinations.
[Off] or 1 or [2].

Latching relays require only CMOS logic which can drive 20 mA with a >2ms pulse for Set, Reset with 2 latching relays (<2A gold plated). They all seem to come in DPDT.

5V logic might be 50 Ohm each so 1V drop on each end so only 3V on coil.

So latching relays demands much more effort with low voltage dropping FET half bridge switches with coil at 5V/20mA=250 Ohms, Ron switch should be <2% each or <= 5 Ohms like a 2N7000 switch 5ohms @ 5V for Nch and similar(?) for Pch.

^{simulate this circuit – Schematic created using CircuitLab}

KEMET UA2-5SNU

Recommendation.

But I think it may be smarter to use a bipolar supply with primary or secondary batteries for non-volatile operation using CMOS Analog Switches using two SPDT channels arrange like above with ESD protection. There are a wide variety of switches from low Ohms to 300 Ohms and wide voltage ranges depending on your needs (xx mV or x V) and R source values.