On Sun, 9 Dec 2012 01:03:49 -0000, in sci.electronics.repair you wrote:

SNIP

The very simple answer is the LM317T. Just Google "LM317T as a constant
current source." Just needs one resistor to set the required current. I
have been using these adjustable voltage regulators as constant current
sources for probably 30 years without issue. Other more powerful three
terminal adjustable voltage regulators can be used in exactly the same way
if you need more current.

Arfa

Hi Arfa,

Yes, you are correct, it is simple! I LOVE IT!!!

I will look though my collection of semis for it (no ECG/NTE sub for it).
If unfound, I will order it or it's equivalent.

Thank You Very Much, John

Even simpler than that.

https://dl.dropbox.com/u/29948706/csce.jpg

Realize though that all the current you want will be going through the pot. Actually best to trial and error it in the beginning and then decide on the resistor value (Re). That tmeans you don't have to screw with calculating those millivolts. Only one diode is actually needed, but using two makes Re less critical so you should be able to fine tune the output more easily using standard resistor values.

The resistor from the base to ground, a wild guess works. Anything from 15K to maybe 47K should work just fine.

That circuit should only need about 2 volts of head voltage, if you need less just use one diode instead of two and adjust the emitter esitor (Re).

You might also put one of the diodes near the battery pack to cut the current back at higher temperatures, but don't let it go open. Losing the connection there will turn the thing on full blast. If you need any thermal integration there are much better ways. If you can give a bit more head voltage you can put a diode in series with Re and it should do the trick, and if it opens up then the current won't max out.