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Joined: Tue Sep 10, 2019 6:28 am

Multiple RFID Reader via RS485

Tue Sep 10, 2019 6:41 am

I want to receive data from three different RFID readers (UART TTL) with one Raspberry Pi.
Due to the fact, that there is a distance about 100m cable length between the RPi and each device, I use a RS485 converter with the RFID reader ... -converter

At the RPi I use a RS485 to UART Hat which works perfectly.
When I connect one of the readers with the RS485 converter to the RPi's RS485 interface I can address the /dev/ttyAMA0 serial port via python and receive data transmitted by the reader.

My problem is, that i am not able to find out the hardware setup to connect more than one rfid reader to the system and receive data.
I read a lot about RS485 and half duplex and multiple senders All of them use a paralell wiring setup. I tried to connect the readers paralell to the RS485 bus but doing this, I do not receive any signal anymore.

Can anybody please help me out? I can't find the error I'm obviously making

Thank you for helping me out

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Posts: 6613
Joined: Tue Oct 09, 2012 11:46 am
Location: Trondheim, Norway

Re: Multiple RFID Reader via RS485

Tue Sep 10, 2019 10:50 am

There is no way to use multiple devices meant for RS-232 on a multidrop RS-485 bus. The devices (and their protocol ) must be designed for RS-485, you need them to only answer/listen to data that has the correct "address".

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