Connecting TWO rfid ID12 failed

Wireless & IoT
1

Hello,

I need to detect RFID tags at 2 different places of a N scale model railway. I use an Arduino Mega 2560 which have 3 serial ports. I connect 2 ID12 readers from ID Innovation (bought here, at SparkFun, not the “LA”). Each ID12 is connected the recommended way (5v to pins 11 and 2, Gnd to 1 and 7, Rx to 9). Serial1 and Serial 2 are correctly set-up on Arduino.

The problem is : when the 2 ID12 are connected, no TTL/RS232 signal is output from both ID12 !!!

But when only one ID12 is connected, it works fine. Both work fine but individually.

The problem does not come from the power supply (I see only a 0.1 v of residual 125KHz), nor from the cabling (frequently checked), nor from the Arduino (I tested also on an MBED, same problem), nor from the software (I have tested many versions).

My software works well when both Rx inputs (19 and 17) of Arduino Mega 2560 are connected together with only one ID12, both read the RFID answer correctly and no char is lost.

I suspected eventually any “near RF effect”. But with a 2 mter distance, the problem is the same.

Does anyone know the solution or have questions ?

Best regards

Dominique

2

dominique.bultez:
I suspected eventually any “near RF effect”. But with a 2 mter distance, the problem is the same.

It appears to me that you've narrowed it down to the one reader interfering with the other. Other than using 2 readers and tags that operate at different frequencies there may be little that you can do. Two ideas come to mind. You can try to shield each reader by creating a well grounded structure around the reader, open only enough "see" the train when it passes a specific spot on the track. I'm not too hopeful that this will work.

You could also try to time share them. Perhaps use the reset pin to turn one reader off while the other is on, allowing ?? 100 msec ?? of on time per reader. I don’t know if the reset pin shuts the RF off and how long it takes the reader to get ready after a reset.

3

Thanks very much : I will try the first one.

For the second one, I am afraid that 2 trains could have to be detected at the same time !

I will be back with the result

Dominique