I have a few questions on batteries and voltage regulators, so I would appreciate any kind of help.
1. Is it a good idea to hook up two 9v batteries to a 7812 to drop the 18 volts? My circuit will be using 170mA maximum for a short period of 10 seconds. Otherwise in standby it will use 20mA and most of the time it will be turned off by a switch.
2. How long will my batteries last and should I get somekind of special 9v? I will have access to the battery compartment to change them, but I'd prefer they would last as long as possible.
3. How do I connect my switch, should I use a DPST to cut off both terminals, or just use a normal SPST?
4. The 12v powers a relay, will the batteries current be enough to turn on the relay?
5. Any other tips would be much appreciated
Cheers!