a barometric pressure sensor
Connect all GND's together, connect all SCL's together and connect all SDA's together => Done!Be sure to use the Uno as a slave with a different address. And don't use long cables...
A barometric pressure sensor that operates on five volts?
did you put pull-up resistors on SDA and SCL ? if not, you should give it a try (4k7 between +5v and SDA and 4k7 between +5V and SCL )Did you try an i2c scanner to make sure the Uno and the sensor actually have different adresses and are both recognized ?