I have put together the well known DIY tDCs-device Inthinkerator MK1, and wanted to add an extra safety feature, but I dont know if this is the correct way to do it. The original design is without the 2N4393, but I've added it.
tDCs stands for transcranial Direct Current stimulation. The concept is nothing new, but has gained alot of attention lately. Alot of research is being done, and there is alot to read about it. https://www.ncbi.nlm.nih.gov/pubmed/?term=tdcs is one source.
(You can also search for snake oil, but it does'nt seem to have the same medical application potential... https://www.ncbi.nlm.nih.gov/pubmed/?term=snake+oil)
My plan is to set a max current on the 2N4393, so if something went wrong with the original setup with 2N3904, it still would'nt go over set current limit. That's my plan at least.
By setting the trimpot at 2N4393 to never let it put thru more then 2,5mA, and then use the 5k pot to 2N3904 to be able to change the output from 0,36 to 2,0mA.
Can someone say if this is a bad idea? The simulation in Qucs "says" it will work as intended.