Hi John et al.
thanks for the responses. I am still a bit confused, so I've prepared a diagram of the circuit I'm trying to put together (sorry - it is rather crude). Please see attached.
So, basically, I have a Logomatic V2 data logger that I want to be able to switch on and off by means of a digital pin. Since it uses up to 80mA, I cannot connect the datalogger's X1 directly to an arduino digital pin, so I have to use a relay that keeps the data logger's circuit separate from that of the arduino. In this way, I can have the relay serve as a switch that completes the connection between X1 and X2 (to turn on the logger while keeping this circuit separate from the arduino) based on a signal from the arduino.
In the diagram, I am using pin 8 as the digital output pin to control the relay. Although I am starting to better understand how this works, I am still confused on a few things (sorry for the many questions... thank you for your patience & guidance!!):
a. where do I connect the "relay power V+"to?
b. where do I connect the "relay power GND" to?
c. can I connect the "GND" (bottom of sketch) to the arduino GND?
d. would X1 be connected to relay pin 13?
e. would X2 be connected to relay pin 9? (this way, would the logger turn on when the arduino pin is set to OUTPUT?)
Any advice & suggestions would be great... Thank you SOOOO much!!!