Need Help with Isolated Button Control for Relay Driver - Page 1
Forum section: electronics / projects

author: funky2x
author_rank: Contributor
timestamp: April 10, 2025, 08:40:51 pm
content: Hey everyone,I’m working on a project where I need a mechanical button to control a relay driver, but I’m stuck on how to do it while keeping the button and the relay driver circuit completely isolated from each other.What I’m aiming for:The button should only open or close a circuit when pressed.There should be no direct connection to power or ground in the button circuit.The relay driver circuit should be activated by the button press, but it needs to stay isolated from the button, without any interference.Has anyone done something like this or have any ideas on how to make it work? Any help would be greatly appreciated!

author: themadhippy
author_rank: Super Contributor
timestamp: April 10, 2025, 08:45:35 pm
content: kinetic switch?

author: funky2x
author_rank: Contributor
timestamp: April 10, 2025, 08:54:01 pm
content: Momentary / tactical switch

author: themadhippy
author_rank: Super Contributor
timestamp: April 10, 2025, 09:09:42 pm
content: kinetics do come in momentary ,commonly used for door bells.No power or indeed any wires required at the switch,just the receiver and that would come from the drive circuit.

author: bdunham7
author_rank: Super Contributor
timestamp: April 10, 2025, 09:11:49 pm
content: Quote from: funky2x on April 10, 2025, 08:40:51 pmHow isolated? What voltages are involved? There are pneumatic remote controls that are used in wet areas like spas, pools and my garbage disposal. The button is a piston/cylinder and there is a plastic line that goes to a remote switch activator.If your button must be electrical and connected via wires, then perhaps have an RF signal going to a transformer of appropriate specs and isolation and have the button short it. An appropriate receiver circuit should be able to sense that.

author: Eddio
author_rank: Newbie
timestamp: April 11, 2025, 11:04:02 am
content: You can use optical isolation.

author: PGPG
author_rank: Frequent Contributor
timestamp: April 11, 2025, 03:32:46 pm
content: Quote from: funky2x on April 10, 2025, 08:40:51 pmSeveral years ago I got an idea of detecting L change (1..3 coils on very high permeability toroid) caused by conductance of circuit containing wire going through toroid center.I have just made experiments to check L/R time constant change and made a device that distinguish situation when the wire is opened and shorted by some resistance. I'm sure that I got a circuit that shorting by 10 ohm was always detected. I suppose that border was at 20...100 ohm depending on core parameters (high permeability cores have very large parameter dispersion).If you do not need to tolerate some resistance in circuit, but you have only the switch than the problem should be simpler.You can detect several ns time constant changes using LVC gates.According to what I remember in my solution I have 10Hz generator and at one of its slope I compare LR time constant with some RC constant by two delayed slopes driving D and Clock inputs of D flip-flop. So at Q output I have the input state but delayed by 1/10s. As detection takes only some ns you can do it much often than I.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: April 12, 2025, 11:04:42 pm
content: Quote from: funky2x on April 10, 2025, 08:40:51 pmSo you mean toggle on each press ? That needs a flip-flop, or a push-push switch.Quote from: funky2x on April 10, 2025, 08:54:01 pmIf you mean tact switch, those are usually momentary only.Do you have a photo of the switch and any size limits?Quote from: funky2x on April 10, 2025, 08:40:51 pm'completely isolated' is too vague to be useful. What voltage or distance limits do you actually have?You can use OptoPV and OptoNPN isolators for 2500V~5300V isolations, and you add a FlipFlop for toggle operation, and a MOSFET for relay drive.

author: inse
author_rank: Super Contributor
timestamp: April 13, 2025, 06:48:48 am
content: I recently came across a socket mount relay that had a mechanical test button to engage the contacts - is this what you are looking for?