Re: ATM A little electronic help on my Foucault tester

[Del Stanton <sd20@earthlink.net>]

The longer of the LED's two leads is the one to connect
to the positive end of the battery.  The fixed and
adjustable resistors can go on either side of the LED.
or on both sides of the LED.  All are wired in series,
so that the same current passes through everything, the
batteries, the LED, and the two resistors.

A 9 volt battery is an expensive way to buy electrical
energy.  It has six very small cells wired in series. 
Further, when you use a 9 volt battery to drive a 2
volt LED 7 volts goes to heat the resistors while 2
volts lights the LED, thus you are wasting 7/9ths of
the expensive energy of the 9 volt battery.  With two
1.5 AA batteries in series you will be using 2/3rds of
the voltage to light the LED and 1/3rd of the voltage
to heat the resistor.  Thus it is much better to use
two AA batteries in series.  Get a battery holder from
Radio Shack: It is surprisingly difficult to make
reliable contact to batteries with when you attempt to
improvise instead of buying a battery holder.

Del Stanton  sd20@earthlink.net