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I am working on a project with 3 PCB : PCB1 is the master, it communicates with two slaves, PCB2 and PCB3.

PCB1 is powered by a battery and it redirects the supply to PCB2 and PCB3. Each PCB includes a microcontroller and an RS-485 transceiver.

There is a cable from PCB1 to PCB2 and another from PCB1 to PCB3. Both cables are the same. There length is approximately 50 cm. They include 6 wires : 4 wires for the RS-485 (the communication is full duplex), and 2 wires for the supply.

It looks as follows : enter image description here I need to add an ECG sensor on PCB1. It simply measures the potential difference between two analog inputs. The first input needs to be connected to one pad on PCB2, and the other to another pad on PCB3. I was thiking of adding 1 wire in each cable to make the connection. It would look as follows : enter image description here But there would be analog and digital signals in the same cable. Is this a problem ? If so, what are the solution to transmit digital and analog signals at the same time ?

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  • \$\begingroup\$ This question is likely to be answered with opinions rather than facts and citations. It should be updated so it will lead to fact-based answers. - there are insufficient details here. My recommendation is to try it and see what happens then report back should there be enough cross-interference to cause problems. \$\endgroup\$
    – Andy aka
    Feb 26 at 11:53
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    \$\begingroup\$ There be an XY problem dragon here... \$\endgroup\$ Feb 26 at 16:44
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But there would be analog and digital signals in the same cable. Is this a problem ?

It can be a problem depending on the nature of the signals, the type and length of the cable, and what's at either end. In other words, there are many variables.

If so, what are the solution to transmit digital and analog signals at the same time ?

  1. Use cable that shields sensitive signals from one another.
  2. Use techniques like differential pairs, input buffers, etc.

There is no single solution that can be applied to all circumstances.

It appears you are using RS-485. That signaling system was designed to drive long cables. You mention "supply" and I assume you mean power supply. The biggest concerns there are wire gauge so that the far-end voltage is adequate to supply the need.

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  • \$\begingroup\$ I have added the length of the cables. They will not be longer than 50 cm, so the voltage drop would be insignificant. \$\endgroup\$ Feb 26 at 12:00

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