Lazy man's cheat sheet for driving latching relays

[noahshreve]

EA2-5TNU from Kemet/Yageo. 28mA coil current. ATTiny absolute max current per port is 40mA, and I feel 28mA is far enough to be safe. It's also just a short pulse to latch the relay, not a continuous load, so there's no overheating. I haven't had any field failures.

Come to think of it, the relay coil won't see a full 5V from the attiny. There will be some voltage drop on the output pin due to the 178 ohm or so coil resistance loading it. So if it sees, say, 4V, it will only draw 22mA. It's guaranteed to latch reliably down to a minimum of 3.75V.

Don't show this to an EE. He'll blow a fuse

You’re a legend

 

[JTEX]

Nah, just lazy. I truly do not know anyone lazier than me. OK, maybe my teenage son.

 

[Robert]

You can also drive a single coil latching relay using a single microcontroller pin and a capacitor.

Pull the pin high to latch the relay (C1 charges through K1)
Pull the pin low to unlatch the relay (C1 discharges through K1 in the opposite polarity)

 

[JTEX]

You can also drive a single coil latching relay using a single microcontroller pin and a capacitor.

Pull the pin high to latch the relay (C1 charges through K1)
Pull the pin low to unlatch the relay (C1 discharges through K1 in the opposite polarity)
View attachment 89743

Good point. I've done it that way too, in a circuit where there was no microcontroller or even any IC at all. Just relay logic (good thing they taught us relay logic back in high school, or it wouldn't have occurred to me). But in a particular pedal I had to use an attiny anyway, so I might as well use it to drive the relays.