Author Topic: ULN2803 Implementation Question  (Read 192 times)

chrisaxeman

ULN2803 Implementation Question
« on: November 19, 2022, 02:15:01 AM »
Hi Guys,

It's been a long time!

Question I have concerns using a ULN2308 to drive some relays. The input trigger voltage for the ULN2308 will be relay driven. Do I need anything like some type of de-bounce circuitry before or after the ULN2308?

I'm building an active breakout box prototype. It is to be used with an RJM Amp Gizmo half-rack function switcher.

The RJM has eight function relays. These are controlled by MIDI messages. The idea of the breakout box is to be able to separate the ground connections from the relays. In their current configuration, mixing the grounds to some degree between relays is unavoidable.

RJM used to offer an active breakout box called the BOB-8 that isolated the 8 relays from one another fully. I thought I'd have a go at making my own.

Type of circuits I was looking at were like some of these:

https://i.stack.imgur.com/Pqto2.png

https://www.twovolt.com/2016/08/24/8-channel-relay-driver-using-uln2803-sugar-cube-relay/

Any help would be appreciated before I get too deep in (I've drilled the box already, so maybe I am).

Another thought I had was something Arduino to give it exclusive control over MIDI, but I'm happy to get this break out box working first, with Arduino being a bit beyond my capability.

Cheers

Chris.
I have no idea what I'm doing,but I like the way it sounds!

Sweetalk

Re: ULN2803 Implementation Question
« Reply #1 on: November 19, 2022, 04:58:24 AM »
I think that any of those circuits will work as you need. The shared ground is on the coil side, not in the switch, so the signal ground will be isolated from each other.

As for the debouce I don't think you'll need any. Wich relay you'll use?

chrisaxeman

Re: ULN2803 Implementation Question
« Reply #2 on: November 19, 2022, 03:00:19 PM »
I think that any of those circuits will work as you need. The shared ground is on the coil side, not in the switch, so the signal ground will be isolated from each other.

As for the debouce I don't think you'll need any. Wich relay you'll use?

Thanks Sweetalk.

Have a bunch of little Fujitsu FBR211 signal relays https://www.fcl.fujitsu.com/downloads/MICRO/fcai/relays/fbr211.pdf

It's all function switching for amps. So not really audio, but part of a bigger picture where I'm trying to avoid ground loops.

Most of the time I could get away with the 4 x TRS setup on the RJM unit as it is. Though as the setup is rack mounted, the breakout box will be mounted in the rear of the rack as an interface. To be able to use it with any of my amps easily is the hope.

Cheers

Chris.
I have no idea what I'm doing,but I like the way it sounds!