I've been battling with getting a modbus wind vane to send data back to a MEGA through a max485 ttl-rs485 converter. I can see the MEGA's TTL signal going into the MAX485 chip, but nothing coming back. Now I'd like to see if anything is actually being converted to RS485 - but my analyzer is a small cheap 5V unit.
I made a voltage divider using 22k and 5.2k resistors to get the 24V down to below 5V but the analyzer doesn't like this, when I connect it all up the channel1 LED goes out, I don't know much about these units but I'm guessing this is not healthy.
Is it possible to measure RS485 with these analyzers? If yes, how do I wire it up?
RS485 uses 5v signals. Where did the 24v come from?
Are you driving the Max485 data enable line? Without that nothing will be sent out.
Don't forget that the voltages on the RS485 A and B lines are inverted with respect to each other. This can be confusing if you are trying to extract meaningful data from the highs and lows.
If your RS484 to TTL converter doesn't already have biasing resistors it would probably be a good idea to add some. This is explained in the RS485 Wikipedia article.
heinburgh:
The wind vane needs 12-24V to operate. I assumed it uses this higher voltage to get the signal across the long distances that RS485 is known for.
RS485 is definitely 5v.
Don't forget, both the A and B lines need to be connected to the RS485 to TTL converter, along with the ground.
Also, the A and B lines need to be the right way round for communication to work.
