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.

Reference

• GitLab?: ​https://gitlab.com/BU-EDF/edf-projects/non-physics/multi-channel-tems
• ​https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf
• ​https://diyi0t.com/arduino-reduce-power-consumption/
• ​https://www.sparkfun.com/products/15140
• ​https://conservancy.umn.edu/bitstream/handle/11299/103933/1/Young_Joseph_January2011.pdf

Implementation

After meeting 10/15/21 with the customer, decided to move ahead with an "Ardunio-based" project.

• ​Schematic (PDF)

One concern with the Arduino shield model is power consumption. According to ​this page (unverified) an Uno R3 uses ~100mA (so 700mW at 7V input). An Arduino pro mini immediately reduces the consumption due to not having built-in USB/serial thing, and it can easily be run on 3.3V and at lower clock speeds. AA batteries are ~2000 mAh while AAA average around 1000 mAh.

Proposed parts:

• Arduino Pro Mini 3.3V ​sparkfun ​schematic
• FTDI Basic Breakout 3.3V ​sparkfun
• Character LCD 3.3V ​sparkfun ​data
• Shaft encoder ​sparkfun (maybe ​breakout board)
• Clear Knob ​sparkfun

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