Connecting Zone Expander to RPi without OSPi

[James]

Hi Ray,

I have 2 of the zone expanders on my OpenSprinkler system, and am now trying to use a 3rd for a miscellaneous control directly from a RPi, but have run into a problem in that a test 24VAC octal relay load doesn’t turn off, although when I initially tested it with a high impedance load (resistor and back to back LEDs) it worked fine.

The zone expander input has the 8 pins:
GND: connected to gnd
GND: connected to gnd
PUR: not connected
VCC: connected to 3.3 VDC
NOE: connected to gnd
LAT: latch signal from RPi code
CLK clock signal from RPi code
DAT data signal from RPi code

Cable length is 6″
Pulse widths are about 1 ms

Any thoughts that might help me, like is the 3.3V ok instead of, and what is the PUR line for?

Thanks for any help you offer

Later…
I have confirmed that the my OSPi zone expanders use 3.3V, not 5V, and yellow PUR wire seemed connected to GND, but connecting it to GND on my new system didn’t help.

I swapped out the “new” version 2.1 zone expander with one from my much older OSPi sprinkling system and found that the problem disappeared! Normally I would use this as an indication that my “new” one is defective, but that seems hardly likely given that I’ve only used it for a bit of testing with the high impedance load mentioned above. Another piece of information is that when my relay turns on properly but then fails to turn off, temporarily removing the relay and then plugging it back in results in the relay staying de-energized. Also, when the RPi code attempts to turn the relay off, the relay audibly and momentarily opens, but not long enough for the larger contactor it is meant to operate to even make a sound.

I will order a replacement if you think it the “new” expander is most likely failed. I need to get my sprinkler system up and running, and can’t backtrack on the changes I’m making to the associated pump and level control system.

Later yet… Close examination of the “problem” reveals that the output component is a Z3M 1 amp Triac, so it is not for DC, and it should work.

31 Mar 2019: PROBLEM CORRECTED! The OSPi also sends an Output Enable signal to the Zone Expander, but my non-OSPi RPi to expander only had Data, Clock, and Latch. Adding the OutputEnable to disable the output while the register shifting was in process has corrected the issue, although this doesn’t explain why the older sytle Rev 2.0 Zone Expander Board worked ok with the Expander’s output continuously enabled.

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