Got my Pi last week, was looking for some diy projects, I think this is the good one to try. I’d like to build one from scratch, so where can I find the schematic of OSPi 1.3? I don’t see it on gitHub, it only has 1.2
Ah, didn’t realize 1.3 files are not in. Just checked them in to Github. One quick note, to avoid confusion: the 10 TVSs are all bidirectional (part number SMBJ48CA). Even though the schematic shows them with a diode symbol, they are bidirectional so non-polar.
I noticed that for the valve driver, you have 8 TVS, my understanding is, the TVS needs to be connected in parallel to the protected circuit. Which is why you have one side connected to 24VAC, and another side connected to the valve. However, I don’t see 24VAC is connection to the expansion board port, so how does this work?
That’s a good question. Indeed 24V AC (COM) is not carried over the extension cable. That’s why on the expansion board the TVS is tied to ground, which is carried over the extension cable. This should still work because there is a TVS between COM and ground, so this is equivalent to have two TVS connected in series between a station wire and COM wire.