I'm using a PIC on a 3v3 circuit to simulate a (normally-open) button press to turn on a machine. To do this, I have some Fujitsu AL3W-K relays. Mine appear to be the double-winding latching type. The nominal voltage is 3V, set voltage is 2v5, and reset voltage is 2v1.

I am new to electronics and I haven't used this type of relay before. It isn't clear to me from the data sheet which pins to connect to my ground and the output pins from my PIC to switch it on/off, and which pins to connect to my hotwired button. There's a diagram that shows a "+" and "-" end of the relay, but connecting those to gnd and 3v respectively doesn't seem to change the connectivity of the pins in between. Maybe I'm not reading the datasheet properly but I am not able to find which pins are which.

How should I connect the pins on my relay in order to simulate button pressing?


1 Answer 1


Probably you want do do something like this:-


simulate this circuit – Schematic created using CircuitLab

The pin diagram is clearly shown on the datasheet:

enter image description here

Note that (for historical reasons) the pin diagram shows the BOTTOM view, rather than top view as most modern datasheets show.

Coils are between 10(+) & 6(-) for SET and 1(+) and 5(-) for RESET.

In the SET state, pins 3 & 4 are connected, and pins 8 & 7 are connected. In the RESET state, pins 2 & 3 are connected, and pins 8 & 9 are connected.

You just pulse one coil or the other briefly to change the state, and it persists until the next pulse even if the power is removed. So if you pulse it to actuate the simulated button and the power goes off before it is released, the simulated button will remain held indefinitely.

If the goal is a simple momentary (not sustained) contact, a latching relay may be a poor choice as it requires twice the drive circuitry of a normal relay and may complicate safety or other operational factors due to it remembering the state.


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