Tiny RTC module doesn't work properly when connected to an Arduino Uno together with 16x2 LCD I am trying to make a digital clock using a tiny RTC, 16x2 LCD, and Arduino Uno. The RTC module works fine if 16x2 LCD is not connected to the Arduino. Both RTC and LCD are I2C modules and hence are using the same A4 and A5 pins of the Arduino. I have been informed that the I2C devices if connected in parallel should work. But, in this case, the clock doesn't show the time properly.
An I2C scanner sketch can help to identify the actual addresses in use. I would use a sketch like on this page https://playground.arduino.cc/Main/I2cScanner or on this page http://gammon.com.au/forum/?id=10896&amp;reply=6#reply6 . Or google 'arduino i2c scanner'.

Hook up the RTC by itself and run the scanner, then hook up the LCD by itself and run the scanner. The output will be on the serial monitor. If the devices have the same address, then that is your problem.

If one of the devices does not show up at all, then perhaps it is defective.