banana jack with interlock shutter - Page 1
Forum section: electronics / projects

author: abeyer
author_rank: Frequent Contributor
timestamp: September 15, 2025, 08:12:36 pm
content: Some multimeters have a mechanical interlock that ensures you can't plug the leads into the wrong jack based on the mode switch...Anyone know of an off the shelf implementation of something like that in a banana jack? Or have vendors all just rolled their own as part of the case/mechanical design?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: September 17, 2025, 02:32:32 pm
content: You write yourself that this is based around the position of the mode switch. So how do you figure this could even be a COTS product? Even if such a system exist, then in what configuration would you want the shutter to operate? Something like 1 out of 5 or further extendable, a bit like the old clunky piano push switches?Also, I never used these, but for me I really do like that my DMM starts beeping at me when the banana plug is in the Amps jack while the DMM switch is in voltage (or another non-Amp) mode. And having to pull the plug out of the jack, and then holding the plug while changing the switch position also seems a bit of a nuisance.Just now I had a look at:https://lygte-info.dk/info/DMMDesignProtection%20UK.htmlAnd lygte mentions 3 other options. Optical with a light beam across the connector (I assume a hole is drilled). Mechanical with a pin though the Banana, and the most common split jack system.

author: abeyer
author_rank: Frequent Contributor
timestamp: September 17, 2025, 05:53:17 pm
content: Quote from: Doctorandus_P on September 17, 2025, 02:32:32 pmDoesn't mean you couldn't package the jack and internal mechanism as a unit with some sort of mechanical linkage needed to the rest of the device that would still be custom. I haven't seen such, and it didn't seem likely, but figured I'd ask if anyone had run across one. I've certainly seen more niche or unusual things that seem to have entire Chinese factories manufacturing them.I was thinking of a use case that's not a DMM and electronic sensing feels like more complexity than is worth introducing. The pin through idea from that link seems interesting, at least, though. Drilling out a hole in a standard jack to accommodate that would be quite a bit less mechanically complex to retrofit than a shutter.

author: shabaz
author_rank: Frequent Contributor
timestamp: September 17, 2025, 08:10:20 pm
content: I don't have a real answer, but had an unrelated issue a while back, where I also didn't want a connector inserted, unless a switch was in a certain position.Since it was just a hobby thing, I went for an unorthodox lever switch (microswitch) arrangement.In the attached photo, it's not possible to plug into the USB socket, because the switch lever is physically in the way. It has to be pushed down to plug into the USB socket, thus ensuring that if ever the user were to use that USB port, then the switch is pressed down.The reason was to do with the top board not being my design, but the bottom one was, and there was some power related issue that I cannot recall.Another option could be to arrange a toggle switch with it covering the banana jack partially. Or 3D-print a rotary knob with a flap that covers it, not great solutions for sure.

author: abeyer
author_rank: Frequent Contributor
timestamp: September 17, 2025, 08:59:30 pm
content: Quote from: shabaz on September 17, 2025, 08:10:20 pmYeah, that's on the lines of what I was thinking about. The pin idea seems mechanically easy enough, and can do a more polished enclosure around that, too, without getting excessively complex. I'm now thinking of having the banana jack through-drilled for a pin interlock, and then a mechanical piece that incorporates the pin itself with an actuator that engages a slide switch.