I’m looking forward to building a DIY DC version of the OSPi and I need a bit of an explaination of the differences between a MOV and a diode for transient voltage protection. Why is MOV better than a 1N4007 diode or a TVS diode? For the v2.3 DC only a MOV was used?
Thanks a lot for this amazing project!
I want to build a unit to control my future garden and greenhouse automatic watering system 😀 Are those 5$ 24V DC valves any good?
MOV and TVS are designed to handle high surge voltage and are recoverable as soon as the high voltage is removed. Standards diodes like 1N4007 are not designed in the same way, and will be permanently damaged if the voltage exceeds their design maximum. Also, they don’t clamp the voltage so they are pretty much useless for protecting the circuit against high transient voltage.
Comparing MOV and TVS: MOV is cheaper but it will deteriorate over time (every time high voltage is present, it sacrifices a little bit of itself to dissipate the energy). TVS diode is more expensive but is more durable, and is available in surface mount packaging so is easier for surface mount soldering.
$5 valves should be good enough. I don’t know the particular model you are looking at, but valves are pretty cheap these days.
I will go with TVS diodes then. Bit offtopic , I installed the newest Unified Firmware from github but it won’t run. I tried running the OpenSprinkler file but it hangs when getting the weather data. What could be the cause? I’m running the newest Raspbian release on a Pi Zero and I can ping the OpenSprinkler Weather service.
If you run build.sh it will automatically add script to start the firmware on reboot. If you want to run the firmware manually, you should first stop the auto-script from running (our support page for OSPi documents how to stop the script), and then you can run the firmware manually by ‘sudo ./OpenSprinkler’.