8 relay module6/13/2023 ![]() ![]() The ULN2803A will work with the 3.3v gpio of the pi, but the ULN2802A probably wont because the Zener on the input will never allow the 3.3v to drive the Darlington transistors as the Zener will never reach the point were it starts to conduct. I don't yet understand the circuit diagram for the GPIO and the relevance of TTL CMOS PMOS as described above but I guess ill have to dust of the old grey matter and go back to first principles again. "Four versions are available to simplify interfacing to standard logic families: the ULN2801A is designed for general purpose applications with a current limit resistor the ULN2802A has a 10.5 kΩ input resistor and Zener for 14-25 V PMOS the ULN2803A has a 2.7 kΩ input resistor for 5 V TTL and CMOS the ULN2804A has a 10.5 kΩ input resistor for 6-15 V CMOS." I ordered ULN2802A then read the data sheet and suspected I might need the ULN2803A
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