To convince ourselves that we could digitally control muscles, our first stimulator would be developed by
modifying an existing commercial stimulator. The conversion involved removing the analog control devices
(switches and potentiometers), and replacing them with a digital display and a computer hardware interface.

Research began by modifying a commercial stimulator (Grass Technologies model S44) to operate via a
computer.



Concept of New Stimulator

The conceptual rendering of the new front panel.

Construction

Midway through the modifications to the commercial stimulator.	The transformation is nearly complete.

The manufacturer was kind enough to supply us with ten pages of schematics that eased our ability to
build and modiy the circuitry.



Printed Circuit Board For LED Display

The new display contains three sets of 4 digit LEDs

The printed circuit board (PCB) fabrication drawing

The schematic used to create the PCB for the LED display


Front Panel Display

With the new digital feedback, we are able to determine the pulse width or duty-cycle, the frequency, and the voltage.

The new stimulator is complete

The new display allows for easy verification that the signal being sent to the test subject is correct.



Additional Circuitry for Display and Conversion to Digital Control

In addition to the display circuitry, there were numerous circuits needed to interpret the signals sent from the computer.

The auxiliary circuits of the High Voltage Contrller, the Frequency Controller, the Duration Controller, and a DC power supply

A crucial circuit was the High Voltage Regulator.

All circuits were simulated in PSpice before being built. The circuit below is a duplicate of the amplifier stage of the
Grass S44 stimulator that was used to verify that the new circuits would indeed perform their necessary tasks.