Is such a device made? - Page 1
Forum section: electronics / beginners

author: Cubbie
author_rank: Contributor
timestamp: May 26, 2021, 04:57:17 am
content: I need to break a wire connection like a toggle switch would do..I want to accomplish this with a cmos logic level. I know I could bias a transistor first.The problem is that I want it to remain in that open state when power is removed.When power is restored, my logic circuit will be reset but I want the "toggle switch"to stay open until I physically push button reset it. I guess I need a externally triggeredcircuit breaker. This is only for 12vdc at 200ma at most.Can't figure out what to use, Thanks, Jim

author: ledtester
author_rank: Super Contributor
timestamp: May 26, 2021, 05:31:48 am
content: So what should happen power up?1) the switch is always open2) the switch assumes the state it was in when power was last removed

author: Cubbie
author_rank: Contributor
timestamp: May 26, 2021, 05:48:58 am
content: 2) the switch assumes the state it was in when power was last removed.Because it was never triggered or it was triggered so now it has to be physically reset.Automobile engine de-mobilizer for a classic car. Delay would be for carjackers. Assuming they can drive a stick. If I park it, I can just pop the distributor cap and pull the rotor.Pressing a momentary button will cause a flip flop to change states biasing a npn transistor which will provide ground to a 555 timer circuit which does not produce a high output for 45 seconds. At this point I want to break the ignition wire or similar. Reset switch or button would be hidden.

author: ledtester
author_rank: Super Contributor
timestamp: May 26, 2021, 06:04:43 am
content: How about latching relay?https://ac-faq.industrial.panasonic.com/en/faq_detail.html?id=41315

author: Cubbie
author_rank: Contributor
timestamp: May 26, 2021, 06:13:58 am
content: Yes I considered a latching relay and even a SCR. I was hoping to physically press a switch to reset it but, maybe that will not be possible.. Thanks.

author: ledtester
author_rank: Super Contributor
timestamp: May 26, 2021, 06:24:13 am
content: If you have power some circuitry could translate the press of a push button to generate the right impulses to the relay's coil to toggle or reset it.

author: Cubbie
author_rank: Contributor
timestamp: May 26, 2021, 07:04:16 am
content: Yes, thanks for your input ledtester, I was thinking I could even use a small battery to toggle the relay back to the closed state since the car is only used in the summer months. That way resetting the relay would be totally independent of the car's 12 volts.Anyway, I got some ideas, Thanks.

author: jh15
author_rank: Frequent Contributor
timestamp: May 26, 2021, 02:42:33 pm
content: I used to just put a hidden switch to turn off the fuel pump. Oh, and the gas guage, to make it look empty.

author: Gregg
author_rank: Super Contributor
timestamp: May 26, 2021, 09:05:23 pm
content: The simple and reliable solution is an automotive relay and a momentary normally open switch.Ignition provides power to the momentary switch which turns on the circuit and when the relay closes it also self powers until the ignition is turned off which resets the circuit.I used this same circuit on my MGA when I rewired it. I had a tiny push button switch hidden where I could reach it under the dash while turning the ignition on so nobody would notice. You also could use a hidden reed switch that would require a magnet to initiate.

author: Cubbie
author_rank: Contributor
timestamp: May 27, 2021, 08:17:26 am
content: I think I might try a magnetic latching relay for this project. Can someone tell me how this 12 volt coil is controlled. Is polarity switched to get it to change states?

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 01, 2021, 02:03:45 pm
content: Some latching relays have external set and/or reset buttons.You may also have success with a magnet on a lever.Or you can do as normal people do, and use an extra switch to send current through one of the relay coils.