I am controlling a MCP23017 to expand the number of GPIO through i2c.
Basically I use pins 3 and 5 for i2c.
When I power up the circuit using the +5v and ground from rpi pins 4 and 6 I can run my program written in golang and it works fine.
But when I use a computer power supply to power the MCP23017 with 5V (red) and ground the rpi cannot detect anymore the chip on the bus.
i2cdetect -y 1 does not detect anything despite my control LED is up.
I am then wondering if the i2c bus of the rpi is only enabled / active, when there is a minimum load on the other pins.