Help Finding Relays to Buy for a Raspberry Pi

Thread Starter

ChipResearch

Joined May 23, 2022
3
I'm building a custom "wallbox" for my 1952 seeburg jukebox.
This custom "wallbox" will be a Raspberry Pi inside the jukebox, which'll let me make song requested from my phone.

The jukeboxes original wallbox sends song requests by rapidly pulsing a 48V signal (it gets 48v from the jukebox for power, but also pulses it on a "data" wire that returns to the jukebox) I know the exact timings of the signals for every possible request, and I could replicate said signals using a microcomputer and a relay

I have sorted out almost everything, except for a few good relays, which need to handle 48v load, (no amps to speak of as this signal just operates a relay in the jukebox) And the relays must be able to switch rapidly (a max of 26 pulses in less than 3 seconds).

I want 2 relays since I have a second signal wire to run to skip songs. Originally, I tried some simple 3v relays to switch with the pi's logic outputs without any extra power, but it turns out to be dumb. The relays start to move, but don't completely click. I could try linking 2 logic lines together for double Amps, but it seems risky and wrong.

Thus, I need a recommendation for a couple relays I can get on Amazon Canada/US that would work wonders with a Raspberry Pi. I can run a secondary power supply to it. Preferably 5V. Thanks!
 

Alec_t

Joined Sep 17, 2013
13,044
Welcome to AAC!
It's not a good idea to drive a mechanical relay directly by an MCU, because of possible MCU damage by the voltage spike the relay coil generates when the coil switches off. Have you considered using solid-state relays instead?
 

Thread Starter

ChipResearch

Joined May 23, 2022
3
Welcome to AAC!
It's not a good idea to drive a mechanical relay directly by an MCU, because of possible MCU damage by the voltage spike the relay coil generates when the coil switches off. Have you considered using solid-state relays instead?
Thanks for your reply and suggestion! I think you have a good point and I will give it a try :)
 

ErnieM

Joined Apr 24, 2011
8,328
Several places make relay modules with a driver for something like a Pi to drive them correctly. Here's one: EBay Link

This is a 12V relay, so you need to power that correctly. They also come in 5V versions which may be better for you.

You want a "signal relay" (<2 amps) because the higher current ones (like 10A) don't do so well with small current switching over the long haul as they need some current to keep the contacts clean. Signal relays don't have that issue.
 

2Pringles

Joined Apr 9, 2022
33

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MisterBill2

Joined Jan 23, 2018
12,697
You should be able to use a transistor if the 48 volts is DC . But you should also be able to drive a reed relay with a transistor from your processor. Use a transistor with a higher voltage rating, over 100 volts would be good, because a diode will slow the relay drop out quite a bit. It certainly IS possible to run an inductive device without damaging the switching device just by using a transistor with an adequate voltage rating..
 

dl324

Joined Mar 30, 2015
14,902
I need a recommendation for a couple relays I can get on Amazon Canada/US that would work wonders with a Raspberry Pi. I can run a secondary power supply to it. Preferably 5V. Thanks!
Raspberry Pi's operate at 3.3V, so 5V relays are out.

If you show a diagram of what you're planning to switch, members can offer some better solutions.
 

MisterBill2

Joined Jan 23, 2018
12,697
You can certainly drive a relay switching 5 volts with a 3.3 volt signal. Use an NPN transistor in the open-collector arrangement to pull down the relay coil, with 5 volts on the relay.
 
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