Max485 no differential voltage

I've got a handful of the MAX485 boards. I've hooked a couple of them up for test (5v Vcc, High on the DI-DE-!RE, NC on the RO) and I expected about 1.5v differential on the A-B pins, but I've got only 12 mv. Tried it on three boards, same thing.

With DE high, I didn't think I'd need a failsafe pullup network or even the 120 ohm load resistors. Am I missing something?

Dr Q

Dr_Quark:
I've got a handful of the MAX485 boards. I've hooked a couple of them up for test (5v Vcc, High on the DI-DE-!RE, NC on the RO) and I expected about 1.5v differential on the A-B pins, but I've got only 12 mv. Tried it on three boards, same thing.

With DE high, I didn't think I'd need a failsafe pullup network or even the 120 ohm load resistors. Am I missing something?

Dr Q

And no ground to the Arduino and power?

Paul

Paul, comeon. You can’t have +5 Vcc if you don’t have ground. You’ve just got a wire that wishes it was +5. :o
Dr Q

Was not in your list of connections.