Hi folks,
I am trying to build simple circuit that switches on small pump (via relay) when soil gets too dry. I am using capacitive moisture sensor connected to 3.3V pin. It all works fine during Arduino debugging when Arduino is connected to PC via USB. However it does not work if I disconnect it from PC and try to run on external 5V power source connected to Vin and GND on Arduino Nano. Looks like Arduino does not capture correct moisture reading when I connect my circuit to external power source. What could be the reason? I measured voltage on Nano's 3.3V pin and it reads 3.2V. Could this be not enough for moisture sensor to operate? Should I hook it to 5V instead?
Please post a schematic and an image of the project.
You might want to post your code in code tags.
Ooopps
Why do you think the 5V pin is called the 5V pin?
I read that 5V pin is for voltage supply, i.e. outbound supply. Respectfully Vin is for external power supply for Arduino itself .. as the name suggests 
Glad to do that but the project works fine when power comes from USB. It just fails to switch on relay when on external power supply. There must be something fundamental I am missing. Like, for example, could 3.2V power supply to capacitive sensor be an issue for the sensor to provide accurate reading?
Did you read post#3?
VIN needs more than 5V, use the 5V pin for 5V in.
I use 6V external supply as I am using 6V micro pump.
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