Prototype tACS
Link to tACS alpha (nonfunctional)
Link to first tACS instructable
After working with tDCS devices for a while, I became comfortable (and well-researched) enough with running currents through my head to begin working with tACS. The device referred to here is my first working tACS device.
I got it working but it's a real pain to drive! Replaced with Basic tACS.
Started with an attempt to use PWM through an optoisolator to control the current value but the resulting circuit was too sensitive. Only 8 of the (approximately 256) PWM digital settings were in range so the bit depth of the signal was horribly low.
So I tried a direct USB-to-SPI converter to control a DAC from a computer through an optoisolator. However it was 16ms between DAC updates because the device needed to complete an entire USB handhsake to control the pin required to latch the requested value into the DAC's buffer. Insufficient sample rate.
Then I switched to using a DAC after a digital isolator to send a signal from a computer through a USB-to-serial converter chip and a microcontroller before the digital isolator. This circuit could be made functional but great difficulty in driving it was present with the availiable coding skill of mine at the time. I should now be able to build the tACS properly and have moved it to the project "Advanced tACS".