Hi, I wanted an arduino to control a relay so it would connect a battery to one of that arduino's pins in order to check the battery level as suggested here: http://arduinotronics.blogspot.com.au/2011/03/monitoring-voltage-of-dc-battery-supply.html I will be checking only when certain conditions are met.
Now, I know how to completely isolate the arduino from the one channel relay as shown here: http://yourduino.com/p/OptoRelayChannelData-575.jpg
So my question is:
1) Since the battery's ground will have to be shared with the arduino's in order for the level to be checked then the arduino is no longer completely isolated. I assume this is true?
2) My next question is more important, how about the other side of the relay coil (voltage divider side), is there a danger of emf there? If so, is there any improvement I can do to protect the arduino pin?