Connecting analog pin to MAX 485 output pin -What are the implications

Other Hardware General Electronics
1

Hi All,

I have a PCB where the A2 pin is already connected to one of the 8 pins of a RJ-45 module.
Now I want to re-purpose that pin for another work. I want to connect one of the 2-wire outputs, B, to be specific, from the MAX-485 module (modbus communication ) to this pin.

Thus, practically I am connecting the B pin of the RS485 to A2. This is an undesired connection as I have no purpose of reading the analog voltage level of RS 485 output pins. However, I cant eliminate this connection, since it is through a PCB. The attached picture explains the configurations. The exact model of Arduino does not matter.
My question is: will this configuration somehow destroy my A2 pin or the whole Arduino? Since i am only supplying VCC (5V) to the rs 485 module, the maximum analog voltage level at output pin B can be 5V, which should not damage the A2 pin. Right?
The modbus communication is unaffected by connecting B pin to A2. I already checked that.

Thanks
Souvik.

arduino connection.PNG
arduino connection.PNG1451×669 238 KB

2

The exact model of Arduino DOES matter. Some Arduinos run from 3.3 volts and I suspect that a 5 volt input might be bad for them.

A2 can also be used as a digital input and does not have to be read with the ADC.

Most (all ?) pins can be used digitally and their other purposes (serial, I2C, SPI, PWM, analog input, etc.) is in addition to the digital I/O.

Of course, you still need to be concerned with voltage levels and interference with normal Arduino functions.

3

What is wrong with using a scalpel to cut the track?

4

Or cut or bend the Arduino pin.

5

RS485 bus wires A and B are allowed to vary (common mode) by +/-7V or so by many IC drivers - this means differences in ground potential in different parts of a building or in different buildings can be tolerated. Your A2 pin will not tolerate that sort of voltage.

But if your RS485 wiring is local and such ground potential variation isn't present you wouldn't need to worry about this.

Still cutting the track is easy and brings peace of mind.

BTW I see no ground wire in your bus, RS485 is normally A,B and gnd.

6

vaj4088:
The exact model of Arduino DOES matter. Some Arduinos run from 3.3 volts and I suspect that a 5 volt input might be bad for them.

A2 can also be used as a digital input and does not have to be read with the ADC.

Most (all ?) pins can be used digitally ...

Not A6 & A7 on the Nano.