Need 2nd opinion on Wiring diagram.. proximity - isolation - lpt.

[A_Camera]

Some caution, and breadboarding required here. One problem is we're considering a theoretical model, not an electrical model of the EC300-ETH input circuitry. Once upon a time I sketched this out for this site but cannot find the post now.

It is something like (but not sure how precise, or even accurate this is, or the component values.... and I'm not about to dig out my UC300 to double-check)....



The problem is around the 3v3 operation of the internal logic on the EC300, which necessitates the use of the potential divider resistor network shown in the box on the right of the sketch.

This will allow high-intensity LEDs to illuminate even when the input is off (current path through R4/R1/R2).

OP: Just worth breadboarding one channel when you receive the isolator board. Consider your 300ETH-side LED indicators as sacrificial in the overall solution.

I am not sure this is right. The UC300 uses 5V logic, not 3.3V. Pin 14 of the HC14 is directly connected to pin 26 of the IDC connector #5 where the 5V output is (I just measured). Why would there be such weird voltage divider on the input? Also, the manual clearly says: "All output pins are TTL level with 0/5Volts output Voltage levels and an absolute maximum of +-20mAmps current per output channel. All inputs are TTL compatible and accept 0/5Volts Voltage levels."

[Doddy]

I am not sure this is right. The UC300 uses 5V logic, not 3.3V. Pin 14 of the HC14 is directly connected to pin 26 of the IDC connector #5 where the 5V output is (I just measured). Why would there be such weird voltage divider on the input? Also, the manual clearly says: "All output pins are TTL level with 0/5Volts output Voltage levels and an absolute maximum of +-20mAmps current per output channel. All inputs are TTL compatible and accept 0/5Volts Voltage levels."

Actually, for once I might agree with you - perhaps a half-arsed memory of mine of an aborted project to spin a replacement motherboard for the UC300 daughterboard with onboard ruggedised interfaces - and it describes the interface between the 5V motherboard and the 3.3V daughter card.

Yes, OP, ignore my previous senile ramblings.

EDIT: That's helped me to find the old project under Eagle, completely irrelevant for this thread, but for closure for myself....



That's the equivalent circuit for the daughter-card to motherboard interfaces on the UC300 (in case anyone else wants to ruggedise the UC300)