ospi hat remote from pi

[fatpelt]

would it work to put the hat outside and the pi inside? i have a cat5e cable to the outside of the house so i’d pipe 8 of the pins through that. obviously that would mean the lcd, buttons, sensors (unused), and rf(unused) would either not work, or i’d cable them to the pi directly inside the house. i believe the hat can power itself off the 24vac outside, and the pi could be powered off a 5v usb inside.

if that power works then i think i’d need:
sda (gp2)
scl (gp3)
clk (gp4)
gnd
oe (gp17)
dat (gp27)
lat (gp22)

[Ray]

If you don’t need the LCD, and you don’t use the ADC (analog to digital) sensors, then you don’t even need to connect SDA and SCL. And if you use two separate power supplies (24VAC for OSPi and 5V USB for RPi), then yes you just need GND, CLK, OE, DAT, and LAT.

[fatpelt]

i suppose one other option would be to just put an extension board outside (which i need anyway because of the number of stations i’m running). that has 8 pins, but then i think i’d be pushing 24vac over a cat5. poe is 48v, but, a) this is ac, and b) i think this will be a fair bit more amperage, which would likely be a problem?

[Ray]

The current running on the wires depend on how many zones you will ever run in parallel (concurrently). If you only ever run one valve at a time, the current is about 250mA. Each additional open valve adds another 250mA. With CAT5 wires, the main issue is the wire resistance and the voltage drop. The wire resistance is proportional to the distance, so the longer you have to run the wire the high resistance. That multiplied by the solenoid current tells you the voltage drop. If you know the distance, and it’s a standard CAT5 cable (which I assume has standard wire AWG), and you know how many zones you will open simultaneously, you can ask Gemini or any gen AI about how feasible it is.

[fatpelt]

i would need to find some sort of current clamp to see what’s going over the expander cables, though i expect i’d only run one station at a time. i wasn’t able to narrow down a firm diagram of what the 8 pins are to be sure to make sure i get them right. i’m sure i missed it somewhere obvious.

on the other front though, i’ve patched the 5 aforementioned pins outside and things seem to be working perfectly as you suspected. the hat is powered off the 24v in the pro-c enclosure outside, and all 11 stations run perfectly. the pi is sitting on my desk inside, powered via a 5v brick, happily firing off stations

last couple of things would be to see if i can get the lcd working inside, though i don’t technically need it, and potentially tying in some external monitoring

thanks for an amazing project and support!

[Author]

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