I'm trying to build a robot arm based on Arduino UNO and PCA9685 controlled by few potentiometers. The easiest way that I figure out and find on internet is using two Arduino's, one as master and second as slave. This is where my question comes from, there is a way to use single Arduino UNO instead of two by using at the same time SDA and SCL with analog inputs? Maybe there is another way to do that?

That's my actual code:

#include <Arduino.h>
#include <Adafruit_PWMServoDriver.h>

Adafruit_PWMServoDriver pwmDriver = Adafruit_PWMServoDriver(0x40);

void setup()

int tempPotVal = 0;
int adcPin[4] = {A0, A1, A2, A3};
int pwmRisingTime = 0;
int pwmFallingTime = 0;

void loop()
  for (int id = 0; id < 4; id++)
    tempPotVal = analogRead(adcPin[id]);
    pwmFallingTime = map(tempPotVal, 113, 842, 102, 512);
    pwmDriver.setPWM(id, pwmRisingTime, pwmFallingTime);

2 Answers 2


I2C on Uno/Nano/Mini uses only pins labeled A4 and A5. you can still use 4 ADC pins A0 to A3 on Uno.

  • Yes, you are right! I have absolutely no idea why it didn't work for me before and why I found so many sources on the internet saying that using these two things at the same time is impossible.
    – jadvancek
    Apr 25, 2020 at 20:53

No. You can't. Not unless you could come up with some way of disconnecting one set of devices and connecting the other.

Instead you could add an I2C ADC chip to the existing SCL/SDA bus to expand the number of ADC channels you have available. Or use an analog MUX chip on one of the other ADC pins to expand the number of devices you could connect to it. Or you could add an SPI ADC chip to pins 10-13 (SPI bus) to give you more analog inputs.

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