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How can I connect 2 keylock switches so they would need to be turned simultaneously to make something occur? Answered

Making an instrument panel for my kids with lots of lights/buttons/etc. I was wondering if there was a way to hookup 2 keylock switches so that they would need to be turned at the same time to make an event occur (buzzer/alarm/something light up/etc.). I'm not sure which direction I wanted to go with this. Even if that's not possible, maybe something that would require both to atleast be turned on to make that event occur. Thanks. I've never worked with the keylock switches.


If you have car ignition style switches that don't latch on - the position that makes the starter turn, then just put them in series connection.


+1. The simplest way to implement "AND" logic is to put the switches in series. (Putting them in parallel would be "OR", of course.)

thanks for your help. I'm really new to electronics and circuitry so I will probably have to google what you said to even understand it, but I'm sure I'll figure it out. Thanks again.

"Series" means you connect the switches (or whatever component you're talking about) "one after the other," like beads on a necklace.
When the switches are in series, they both have to be closed for current to flow through.

"Parallel" means that you connect the same side of both switches to each other, then to a wire on the circuit, and similarly you connect all of the other sides together, then back to a wire on the circuit. When the switches are in parallel, either one can be closed, and current will flow through that one.

Wikipedia has a good article with lots of diagrams.

Beating a dead horse !


The switches everyone is talking about are Momentary push button switches !
What is a momentary push button switch ??

Get two Doorbell switches,
connect them in Series like Steve shows.



I would personally go the electronics route and use either a microcontroller or some cheap IC's to make it happen --

My preference would be to use 2 555 timers in whats called 'one shot' or monostable mode. When they do is take an input and convert it to a single output pulse - regardless of how long the input pulse is (from the key switch) - it won't send another pulse until its turned off and back on again by that switch.

Then as you can see you get a limited window of time from each switch that a pulse will be output.

THEN you hook up an AND gate which requires input from both at the SAME TIME to change the output. It's more electrically complex but it does the job wonderfully.

That's pretty much what I would say, have the key switches turning on two monostable 555 timers with a 500ms or 1 second delay or so, as of human error they won't be able to be turned at exactly the same time, then stick the outputs both through an AND gate, or you could probably hook up some transistors to do it too. 555 timers are very good chips, you can create all kinds of things with them. Mostly timing related things like oscillators and timers, but you can also create latches and even amplifiers with a few external components. I got a whole bunch for 18p each. As for the AND gates, about 40p each. A lot cheaper and more fun than programming a PIC or AVR to do it.

As the AND gate output will only be high for the remaining time of the 555 timers, stick it through a latch, my favorite is a C106D Thyristor, they are very cheap and easy to use. When a voltage is present on the gate, they latch on to allow voltage to pass from the anode to cathode (no external power required), a bit like a latching transistor. They can be reset by shorting the anode and cathode.

However, most key switches I have seen stay latched on as they are a physical switch. The circuit I described above would still work in this case, but it could be eliminated completely if you didn't need them to be turned at the same time, simply wire them in series.