@bzublin: I read the document, very nice and detailed write-up. One thing that I noticed is you use DC voltage (30V) and PWM to drive 24VAC solenoid. I’ve never thought about it. Is this a known method to drive 24VAC solenoid? It sounds similar to the control circuit for step motors. I find it fascinating because I’ve always disliked the AC-based system — it’s the industry standard for decades and nobody bothers to change anything, but in modern days DC adapters are way cheaper, lighter, and easier to find than AC adapters, due to their demand. So I really hope the manufacturers will move towards more DC-based controller and solenoids. That’s what motivated me to design the DC-powered OpenSprinkler, which does not use PWM, but the underlying design principle is similar to yours, that is, use DC to drive the solenoid, and making sure the current through the solenoid is roughly the holding current. In any case, I am interesting in hearing more about the PWM method, what frequency do you use, how well does it work, any potential issues you are aware of etc. Thanks.