JTEX
Well-known member
The Cheat: use an ATtiny chip to drive latching relays directly!
Yes, it works, it can put out enough juice, I use it every day, just as seen below. No, you don't even need protection diodes across the relay coils. The chip has them built-in. Some ATtiny chips are available in DIP packages, if you don't want to do SMD.
Here's an example from my current project, where I have to drive 3 latching relays and 3 LEDs, triggered by 3 momentary switches. The idle current consumption (with the right programming, putting the chip to sleep almost all the time) is 300 microamps at 5V, plus maybe 1mA total for the 3 LEDS when they're all on (they're very efficient). The relays only draw any juice at all for about 10 milliseconds, the time it takes them to latch. I used an ATtiny167 because I needed many IO pins, but if you have just one relay, you can use an ATtiny85.
The downside is that (just like I had to...), you'll have to teach yourself how to program said ATtiny chip (use the Arduino IDE), and you'll need to put together a thing called an ISP programmer (In-System Programming). You can easily make one from an Arduino Uno or compatible board. It can program the chip via a 6-pin header after it's already on the board, all wired up with relays and all!
I'm way too lazy to write a longer-form tutorial, but I hope this is enough to maybe spark an idea for someone.
Yes, it works, it can put out enough juice, I use it every day, just as seen below. No, you don't even need protection diodes across the relay coils. The chip has them built-in. Some ATtiny chips are available in DIP packages, if you don't want to do SMD.
Here's an example from my current project, where I have to drive 3 latching relays and 3 LEDs, triggered by 3 momentary switches. The idle current consumption (with the right programming, putting the chip to sleep almost all the time) is 300 microamps at 5V, plus maybe 1mA total for the 3 LEDS when they're all on (they're very efficient). The relays only draw any juice at all for about 10 milliseconds, the time it takes them to latch. I used an ATtiny167 because I needed many IO pins, but if you have just one relay, you can use an ATtiny85.
The downside is that (just like I had to...), you'll have to teach yourself how to program said ATtiny chip (use the Arduino IDE), and you'll need to put together a thing called an ISP programmer (In-System Programming). You can easily make one from an Arduino Uno or compatible board. It can program the chip via a 6-pin header after it's already on the board, all wired up with relays and all!
I'm way too lazy to write a longer-form tutorial, but I hope this is enough to maybe spark an idea for someone.
. It doesn't take that long though. Still, I'm hoping Alpha or somebody else will see the light and make the damn part.
