so i'm using an MPR121 sensor and an Arduino. the ADD pin of the MPR121 is connected to GND so it means that it's address is 0x5A and the I2C scanner works just fine but the problem is that when i connect ADD pin to change MPR121 address the I2C scanner program freezes on "scanning ...".
here's where i got my I2C scanner code from https://playground.arduino.cc/Main/I2cScanner/
schema :
SCL → A5 SDA→ A4 ADD → GND, 3.3v, SCL, SDA IRQ → pin 4
[SOLVED] it was because of hard wiring, the solder bridges on the back of the MPR121 were badly welded.