I Made An RGB Human Circuit And I want you to explain it for me

[noah4546]

I made an rgb led human circuit and I wonder if you could explain how this works Dave.
I Want to know how it senses that you're touching the leads?
(How the transistor read works not the output of led. I wrote the code with my friend)

http://www.instructables.com/id/RGB-Human-Circuit/

[Phaedrus]

The slight difference in ground potential between your finger and the circuit ground means that your finger will produce a very small voltage on the base of the transistor. This is enough to turn the transistor on, which pulls the I/O pin on the MCU low.

The site recommends a normal NPN transistor, but these circuits normally work better/more reliably with a darlington or sziklai transistor pair, as they give a much higher gain, which will better amplify the tiny voltage applied to the base (though keep in mind transistors are transconductance devices)