Hello,
looking for a node that is able to work with RS485.
Is it possible to add an RS485 modul to TheThingsUno?
I would like to read RS485 bus from solar inverter (SMA, SolarData1).
Node can be powered external, so energy consumption is not in focus.
thanks and regards,
Thomas
ThingsUno runs at 4.5V (on the un-regulated side). A device such as a MAX485 really wants 5V, and will provide 5V on its signal lines, which will be too much for the MCU in the ThingsUno, which is configured for 3V operation if I remember correctly.
Since you have no power restrictions, you’d be better off using a regular UNO running at 5V and a MAX485 at either end. Connect A to A and B to B (twisted pair cable) and terminate each end with 120R resistors and you’re off.
See the MAX485 datasheet for more info. Here’s the circuit from the datasheet:
Obviously you only need two 485 devices, not four as shown here. Pay attention to the /RE pin on the receiver end, and the DE pin on the transmitter end. You’ll want to tie the solar charge end of the 485 link such that it can always transmit, and the MCU end such that it always receives. Note that these are half-duplex devices - you cannot send and receive simultaneously.
The MAX485 datasheet is available here:
The MAX485 is available from RS components (and of course other suppliers). RS part no is 540-2243.
Regards
Mark
We got a reference design for RS485 <> LoRaWAN.
Still interested?
Yes. Still looking for hardware.
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