I am working on Intel Galileo board and using its one ADC pin (A5) and one digital GPIO pin (pin 8).
I am switching a relay from GPIO pin and using ULN2003A for isolation and LM60 temperature sensor attached to ADC.I have given power to ULN2003A IC from board only.
Now the problem is when GPIO pin is logic 0 (relay is open) ADC output at room temperature is 125 but when GPIO is logic 1 (relay is closed) ADC output increases to 127.
To debug it I have done below permutations:
-I disconnected relay from isolation IC (ULN2003A) then there is no change in the ourput of ADC (it remains constant).
-I have used electro-mechanical relay and solid state relay but having the same problem.
-I measured voltage with relay connected when GPIO is logic 0 (relay is open) is 4.95V but it drops down to 4.93 when GPIO is logic 1 (relay is closed).
-When a separate power is given to isolation IC (ULN2003A) (from another power source) it works perfectly (ADC output remains constant).
Schematic is below:
I am unable to understand why ADC output is changing with switching of relay.