i could use some advise please

Thread Starter


Joined Jun 5, 2007
hello everyone , I am fairly new to circuitry and I have had a question for a while that I am unable to find an answer to. any help would be greatly appreciated.

what I am trying to do is build a metal detector using plans I had discovered at this websitehttp://home.clara.net/saxons/bfo.htm

I am trying to add an LED to indicate wheather the device is on or not. I understand that I have to hook up a spst switch with the battery +, but if I hook up a properly resisted 2.1 volt LED parallel to the whole circuit will that decrease the amount of power the rest of the circuit is recieving? how do i get an LED in there as to minimalize the impact on the rest of the circuit?

Also does anyone know if you NEED an oscilloscope to measure the frequency of a coil? can i just do it with some other method? Thanks a lot again!


Joined Jan 10, 2006
An LED shouldn't impact on the circuit too much. If you use a 1k resistor in series with the LED the extra current would be in the order of around 7 mA. That would barely reduce the voltage from the Battery unless it were an extremely poor quality chinese Carbon Zinc.
The better the battery you use, the better the battery life you will get.