Transcerebral Direct Current Stimulation is one of those scary phrases that conjures up images of white tiled Victorian hospitals with an overpowering smell of bleach, but apparently it's all the rage. In the last few months there has been an article in New Scientist and a couple of posts to Boing Boing so it's not going to be instantly fatal.
|tDCS Stripboard Photo|
The circuit itself is simply a LM317 configured as a constant current source set to 1mA, with a LED battery test function. By choosing a 1k ohm current limiting resistor for the test LED I was hoping that it would be a helpful feature, but, unfortunately, it still lights reasonably brightly even when Vbatt is down at 3v. This means that it's not very useful as a battery test, meh.
|tDCS Circuit Diagram|
A more useful battery test feature would be to turn on the LED when Vout approaches (Vbatt - Vdo), as this would be the point that the battery is no longer providing enough voltage to maintain 1mA through the probes.
Measuring the output current using the internal resistance (tiny) of my multimeter it was reading 1.02mA - and a very low resistance load is a worst case for compliance, so I'm happy that it is to specification.
So, Mr S. if you do actually try using this, please don't turn yourself into either a superhero or a vegetable, I'll never hear the end of it.