I found this tutorial of how to connect arduino to a relay. http://www.arduino.cc/playground/uploads/Learning/relays.pdf
It connects to the relay through a transistor. My question is is the transistor really needed, or can I just connect the arduino output to the relay controll itself? Assuming relay has turn on voltage of 3V and off voltage of 1V.
Also, I connected the arduino's analog input to a power supply and I get the desired output, but when I connect to my instrument (250mVDC, amplified output from a thermocouple), the output function is inverted. What can be the problem
thx in advance