Flip-flop relay? (small pulse to open/close great current)


I was wondering if there exists such device that acts as a relay, but only needing power to change state (i.e. not continous power supply in order to keep the circuit closed)


Yes it is called a latching relay and has two coils one to switch it in one direction and the other coil for the other direction.

That was fast! Thank you!

One last thing: latching dual coil, or single coil?

is it on dual coil you power one or another to switch and in the single coil, every time you power it up ("rising edge", let's say) changes the state?

I'm talking about DPDT in case you need to know that too

You can get both types, single coil with a change in current direction or two coils. Do a search.

There are also "ratchet relays" which a single pulse will throw the relay one way and each additional pulse will throw it back the other way. The difference between this and the latching relay is you dont need to reverse the polarity to change the state of the relay

Actually, that sounds more like the type of thing I'm looking for, would solve a lot of components to reverse the polarity, etc.

The only problem is that after a quick search on digikey, all ratchet relays cost over $100!

You probably could wire a circuit so that a pin would be the 3-state like charlieplex with input-w/pullup doing nothing the output-HIGH switches on and output-LOW switches off.

I dont know what your requirements are as far as what kind of load you need to switch, but Altronix makes ratchet relay RBR1224 which is reasonably priced.


You could trigger it directly from the Arduino, too. You would put a constant voltage on the + and - terminals, and use the Arduino to pulse the trigger.

Here's the link to the data sheet for the relay


Note that you need 12 -24VDC for the relay but you can trigger it with 3 - 24VDC

Hm... I was thinking about something to a lower scale. A simple, cheap DPDT relay that can be "flipped" without too much circuitry around. Anyway, flipping the current can be achieved by setting two pins in the arduino to low and high and viceversa, right? Could that solve it?


What is wrong with this then?

Yeah, that's pretty much what I'm looking for. It's quite expensive though, I'll google around to see if I can get a better price for them (I need a bunch of them!)

I think your idea of expensive is quite unrealistic, you might be able to get them cheaper but that is a good price. They are five times that from farnell

I don't know how unrealistic is because It's the first time I buy these devices. I'm going to build about 30 modules that would likely need about 2 or 3 of these. That kind of doubles the price of the module itself taking into account the components it already needs. If they are all around $6 then I might consider getting just regular DPDT relays.

Sorry if I'm being a bit picky, but I'm new to all this stuff!

What have you done to me? I went off to eBay, just curious, and now I've ordered some!

The OP is in Spain, so....

... from the UK should be attractive? GBP 1.25 + reasonable shipping. (GBP1.50 to UK address)

These have 5v coil, separate coils for "set" and "reset".

BUT! If you don't need the "latching" aspect, why not just ordinary relays? Should be cheaper.

Even if you do need latching... with the Arduino's "write to (built in) EEPROM" capability, you can have "preserve relay state across power cycle". Of course this option won't (always) do what a latching relay will: maintain the relay state DURING a power fail... but whatever it is controlling will be "mis-behaving" during the power fail, anyway, won't it?