Multi channel TEMS

This page describes a proposed mult-channel transcutaneous electrical nerve stimulation (TENS) device for Dr. Mario Cabodi’s biomedical device design lab (BME). Here is some description from the customer (N. Vellanki):

"Transcutaneous electrical nerve stimulation (TENS) is when a device is used to send small electrical impulses onto the skin to override the nervous system to provide pain relief. It’s used to help patients suffering from chronic pain and is usually a single channel device and I’m trying to make a multichannel version for experimental purposes."

Figures provided by the customer below.

The customer has asked for a quote on a complete four-channel circuit, battery-powered. The existing circuits use a single 9V battery but we propose to use 8 x AAA or AA batteries to provide 12V and longer battery life.

Reading

Here are some interesting papers I've found.

• ​https://conservancy.umn.edu/bitstream/handle/11299/103933/1/Young_Joseph_January2011.pdf

Implementation options

Option 1

• 555/556 or similar analog timers as in the circuit above
• Additional timer to multiplex channels
• CMOS divide-by-four counter
• CMOS analog multiplexer
• Four drive circuits with MOSFET, transformer

Option 2

• Arduino or other uC driving MOSFET gates directly, with PWM amplitude control.
• Either a computer interface or display/buttons to change parameters
• Four drive circuits with MOSFET, transformer

Option 1 is the most straightforward to build; no software. BUT in the end there are several analog adjustments, and I question how one can do repeatable experiments with such a device without any easy way to record and reset the settings. At the least one might want to use 10-turn pots with dials.

Option 2 would use the fewest components and be most compact. Digital settings would be 100% repeatable. A computer interface would be easy to provide if wanted. BUT it would require a substantial software project.

Cost estimate

    Engineering                        Either   Option 1    Option 2
    Discussion, specifications          1 hr
    Schematic capture                            3 hr        1.5 hr
    PCB layout (either option)                   3 hr        2   hr
    Assemble, debug, test prototype              1 hr        3   hr   
                                        Total    8 hr        7.5 hr
    PCB fabrication (JLC)  $20
    Parts (wild guess)     $50 ea

    So maybe $1500