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  1. If your resistor is really a constant 20 ohms, then you only need a variable voltage source with a range of zero to 2.4V, which is what Indulis's circuit does (although it may oscillate). A current source provides constant current independent of the load. Does your load vary? If so, I can provide you with the schematic for a variable constant current source.
  2. Google "float switch". I found some inexpensive ones, and plans for a homemade one.
  3. Is there some reason you can't use a switching regulator? A 10 amp linear regulator is bulky, expensive, and hot!
  4. Do a Google search on "kill-a-watt". You can buy one for around U.S. $20 - $30. Of course, if you really want to build one, you could learn a lot.
  5. I use Linear Technology's LTSPICE/SWITCHERCAD III. It's totally free, but is not easy to use unless you have a good understanding of Spice.
  6. How about a digital pot driven by a variable-frequency oscillator (555)? Maxim, or other mfrs, may have other parts that will work as well or better. Google (digital pot".
  7. Great explanation, AG!
  8. I see that now. I'm sure glad I pre-apologized for missing it! :)
  9. Forgive me if one of you guys already suggested this solution. All you need is two equal-valued resistors and a rail-to-rail I/O op amp. One resistor (Rs) goes from +5V to the inverting input. The other (Rf) goes from the inverting input to the output. The 2.5V-5V input signal goes on the noninverting input. The transfer function is Vout = Vin*(1*Rf/Rs) - 5V*(Rf/Rs).
  10. MP, the National datasheet says the typical minimum current is 3.5ma, but the maximum minimum current (sounds like an oxymoron) is 10ma. Whose datasheet are you using?
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