I just have a quick question.
I'm connecting PN532 NFC reader with RPi, for this I am using around 30m of UTP cable from my front door to rack with RPi, preliminary test showed the device is able to communicate over 30m of cable in UART mode – with data and power each via single pair.
Now I have one pair in UTP cable free, should I use it to double-up the power (3.3V, GND) lines or data (TX,RX) lines which use 3.3V signal? This will drop that pair's effective resistance and increase their current capability. What makes more sense to make it more reliable? Max current is around 100mA for the NFC reader. I measured the voltage at the end while max power consumption at 3.1V (datasheet specifies 2.7V minimum for the PN532 chip)
I don't mean to double the lines for redundancy in case of one pair failing, but to minimize the voltage drop over the long distance of the cable, I am just not sure if giving it the double of the wire gauge is better for data or power (either using one whole pair for GND, second for 3.3V power, or one wire of each pair for RX and one of each pair for TX for data – to keep the benefits of twisted pair).
Thank you
Best Answer
Since there are no more comments here, to sum it up:
With this setup there should be one pair for each TX and RX, where in one pair there are TX and GND wires and in second pair there are RX and GND wires, but this set up will not work reliably over such a long distance.
To make this connection work properly RS-485 or RS-422 should be used, which use differential signals.