Connect latching relay

I got a bunch of latching relays for my wifi tank project, but how do I actually connect them?

They got 2 sets of switches, and to activate one position, you add 5V across the coil, and to activate the opposite, you connect the 5V the opposite direction.

More information needed as to what you are trying to do.

Until now you have answered your own question. Powering one coil triggers relay, which then latches, and powering the other releases it.


How to connect it to the arduino of curse, I just need to be able to switch it back and forth, without ems from the coil damaging anything.

Google the "H bridge", that's one way to solve your problem. Tom

Below is info from a commercial relay board with a schematic showing how to put a diode across the relay coil to prevent damage to the controlling transistor. This is for a parallel port, which is similar to the output of the arduino.

Doesn't look like a latching relay zoomkat... To switch this from one position to another, I need to reverse the voltage.

It only needs it very short, and it will then stay there without any voltage applied to it, until the polarity is reversed.

The below has info on making a small h-bridge setup that may be needed to do the polarity switching. Latching relays might have a down side as on a loss of power and such, they may be failed in an undesired position.

Latching relays might have a down side as on a loss of power and such, they may be failed in an undesired position.

True, and that is exactly what I need it for ;)

I am using it as a self-kill switch for my tank. So when the voltage drops below 7 volts, it pulls the relay, and switches itself off, and will first be switched back on again when I manually do it, which is how I want it to be. :)

Will try to build that bridge.

No, because it is not a power fail, is is the voltage dropping to a certain point.

I use my voltage divider to measure the voltage, and if it drops to, or below, 7v for more than 2000ms, the Arduino will turn itself off, without an option to turn itself on again, and without having to hold the relay all the time.

If the power is disconnected, and then reconnected, it should power up again and return to the state it were in before.

I have one question concerning the H-bridge. I purchased some bistable relays (small print relais Matsushita DS2E-SL - DC3V) I found a simple method in some other Forum to use them, but I am not sure if there is any reason not to use it. If the Pin is high, Capacitor is charged and Relais switches in one direction. If the Pin is low, Capacitor discharges and switches Relais back.

Pin | | - Coil | + | ____ Capacitor 100µF | GND

Is that allowed? (it works fine) Or can this damage the Arduino on long term?

Below is a link to a auto power off circuit I built that utilizes a single coil 5vdc latching relay. This relay coil only draws 13ma so no transistor switches or H-bridge required. The series cap serves two functions, one to eliminate continuous current draw while in the set mode (while the digital output pin is high) and to store a charge to allow a brief reverse current flow when the digital output pin is brought low to reset the relay. Note that you can NOT use a parallel diode across the coil as it would allow current to bypass the coil in one direction and prevent the bipolar current flow through the coil required of single coil latching relays.

The circuit works as follows, user presses manual momentary switch to power processor chip, first steps in the chip’s program sets the output pin high to set the relay and seal the contacts across the manual switch thus allowing power to be latched on. As the cap charges fully current stops flowing. When the program wants to power the board off it just has to bring the output pin low which resets the relay removing power from the board.

This could be useful for applications where the board is powered with Li-po batteries where you could measure the battery value via analog input (voltage divider may be needed) and have the program turn off the board when the battery reaches end of charge voltage, thus preventing over-discharge damage to the Li-po battery.

The relay I used is still avalible on e-bay at a nice price: