Advanced tDCS
Link to github repository of board file and schematic
The construction of advanced tDCS is here used to refer to the production of a device which is optimized for small size and low production cost. By switching to mostly surface-mount parts it is possible to decrease the raw cost of materials to ~$12 (as of 2016) per unit. Addition of an integrated shunt regulator instead of the quick-and-dirty old standard three 1N400X diodes enables the feature of low voltage indication with only one additional part. The harder knee on the V-I curve of the integrated shunt reference allows the voltage to be kept constant even as the current through it is varied, moreso than a P-N junction diode would allow. The power indicator LED is attached to a resistor divider and drains into the voltage reference such that the LED ceases to light once the battery voltage falls to about 25V.