https://devzone.nordicsemi.com/f/nordic-q-a/14540/using-nrf51822-with-5v-i2cHello I want to connect nRF51822 (on a readbearlab ble nano) to arduino micro which uses 5V logic on a 32U4 IC. I know I can use an external logic level shift, but I need my project to be small. I read in some posts that connecting the I2C lines toen-USTelligent Community 13Thu, 16 Jun 2016 12:46:27 GMThttps://devzone.nordicsemi.com/thread/55543?ContentTypeID=1Thu, 16 Jun 2016 12:46:27 GMT137ad170-7792-4731-bb38-c0d22fbe4515:2d03adca-4a3c-4cb9-b79b-d82f1c806fa3Ole Bauck<p>Having pull-up resistors to 3.3V may work, but it depends on the other chip if 3.3V will be high enough for a logic 1 to be registered. If the logic high threshold is 0.7xVcc, 3.5V for Vcc=5V, then it will be just below, so you will be living on the edge. The best solution is probably to add that level shifter.</p> <p>I advise you to read <a href="http://playground.arduino.cc/Main/I2CBi-directionalLevelShifter">this</a>.</p><div style="clear:both;"></div>