enter image description hereIm working on a project where I want to connect 32 servos together. I got: -Arduino uno -2 PCA9685 16-Channel 12-bit PWM/Servo Shield -power supply 5v 10 A -All wiring is to the right pins (I have checked that several times)

So I got the 2 PCA9685 16-Channel 12-bit PWM/Servo Shield from Adafruit I connected all the wires as its supposed to be and I connected the shield to an external power supply which is 5V 10A that should be sufficient for it to work but unfortunately servos are not moving at all although the serial monitor is giving numbers I don't know where is the problem coming from. ps. Im using the Adafruit library its not even moving one servo (although the servo moves when connected directly to the Arduino. thank you in advance.

the code I'm using its one of the examples from the library:

  This is an example for our Adafruit 16-channel PWM & Servo driver
  Servo test - this will drive 8 servos, one after the other on the
  first 8 pins of the PCA9685

  Pick one up today in the adafruit shop!
  ------> http://www.adafruit.com/products/815

  These drivers use I2C to communicate, 2 pins are required to  

  Adafruit invests time and resources providing this open source code, 
  please support Adafruit and open-source hardware by purchasing 
  products from Adafruit!

  Written by Limor Fried/Ladyada for Adafruit Industries.  
  BSD license, all text above must be included in any redistribution

#include <Wire.h>
#include <Adafruit_PWMServoDriver.h>

// called this way, it uses the default address 0x40
Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver();
// you can also call it with a different address you want
//Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver(0x41);
// you can also call it with a different address and I2C interface
//Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver(&Wire, 0x40);

// Depending on your servo make, the pulse width min and max may vary, you 
// want these to be as small/large as possible without hitting the hard stop
// for max range. You'll have to tweak them as necessary to match the servos you
// have!
#define SERVOMIN  150 // this is the 'minimum' pulse length count (out of 4096)
#define SERVOMAX  600 // this is the 'maximum' pulse length count (out of 4096)

// our servo # counter
uint8_t servonum = 0;

void setup() {
  Serial.println("8 channel Servo test!");


  pwm.setPWMFreq(60);  // Analog servos run at ~60 Hz updates


// you can use this function if you'd like to set the pulse length in seconds
// e.g. setServoPulse(0, 0.001) is a ~1 millisecond pulse width. its not precise!
void setServoPulse(uint8_t n, double pulse) {
  double pulselength;

  pulselength = 1000000;   // 1,000,000 us per second
  pulselength /= 60;   // 60 Hz
  Serial.print(pulselength); Serial.println(" us per period"); 
  pulselength /= 4096;  // 12 bits of resolution
  Serial.print(pulselength); Serial.println(" us per bit"); 
  pulse *= 1000000;  // convert to us
  pulse /= pulselength;
  pwm.setPWM(n, 0, pulse);

void loop() {
  // Drive each servo one at a time
  for (uint16_t pulselen = SERVOMIN; pulselen < SERVOMAX; pulselen++) {
    pwm.setPWM(servonum, 0, pulselen);

  for (uint16_t pulselen = SERVOMAX; pulselen > SERVOMIN; pulselen--) {
    pwm.setPWM(servonum, 0, pulselen);


  servonum ++;
  if (servonum > 7) servonum = 0;
  • 2
    You'll have to show us your wiring and your code if we are to help you.
    – Majenko
    Sep 10, 2018 at 19:59
  • I would suggest running the I2CScanner sketch to see if it can find the chip.
    – Majenko
    Sep 10, 2018 at 20:43
  • I tried now and it gives Scanning... No I2C devices found Sep 10, 2018 at 21:11
  • Ah, I see the problem now...
    – Majenko
    Sep 10, 2018 at 21:13
  • OMG this actually worked but im afraid because it worked before and stoped for the same reason anyway thank you so much 😊 Sep 10, 2018 at 21:24

1 Answer 1


You have your SDA and SCL pins connected backwards.

  • SDA is A4
  • SCL is A5

You have it the other way around.

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