Goal:
My initial goal is to get a single pulse (monophasic) TMS (transcrainial magnetic stimulation)
machine working, then if feasible upgrade the device to rTMS (repetitive ~).
Progress:
LTSpice simulation
(Zipped files as of November 2010). You can download the LTSpice simulation software here. It runs fine under wine in linux.
There are 3 files, replace your "/lib/cmp/standard.dio" file with the included (so you have 1N4007 information)
Have the SCR.sub file in the same directory as the TMS_monophasic.asc file
This is in progress, the SCR seems to be be triggered and dumping a lot of current through the coil in the first cycle(half cycle?) of the AC wave.
Prototype of single pulse TMS
I've been able to stimulate facial nerves (around the right orbit of my eye) with the present setup, I feel as though low ESR (Equivalent Series Resistance) capacitors are needed in order to get the proper pulse waveform to induce current in the neuronal tissue beneath the scalp/skull. I also need an igor to hold the coil to my head, it's hard to tell if you're getting a response from the motor cortex when you're awkwardly holding everything and triggering the circuit yourself.
Parts in setup (as of January 2011):
- SCR marked PRX USA 143-328-003 9827. Bought a pair of these on eBay, the seller was claiming they were equivalent with the C398 (rdr-electronics seems to still be selling these here)
- 3x Sprague Powerlytic(R), electrolytic capacitors [650uF @ 350VDC] (I also have 2 extra ones that I decided not to use on the prototype, just was testing SCR)
- 4 stage Cockcroft-Walton voltage multiplier built with 450v 100uF electrolytic capacitors(electronic goldmine is now sold out, nonpolar capacitors would be ideal) and 1N4007 diodes (these diodes have also been an issue, sometimes they blow up when I forgot to disconnect them from the main circuit, I didn't take good notes when I was playing with the circuit and need to re-do experiments.)
- 4 gauge power cable (from pro-audio shop) 2 twisted leads about 4 feet long from SCR and capacitor circuit to coil
- 6 turn coil wound from flat high current magnet wire and potted with standard epoxy.
- Trigger circuit, 1:1 trasformer to SCR and function generator (this was also an experiment where I ran the function generator to create multiple pulses, but some diodes exploded...)
Photographs:
Team:
Consists of a non-centralized, ad-hoc, "do-ocracy". I've recieved simulation help from my grandfather, who pointed me in the direction of LTSpice. If you are doing work on something similar or would like to contribute information (in any form, material, idea, et cetra.) please feel free to email here:
uberscientist at gmail.com
