The Future

The device was effective and rudimentary which is good for simplicity however a digital approach seemed more cutting edge so an Arduino simulation was made.

A pair of push buttons were connected as digital inputs that will change the desired current output with 1 mA intervals this could be changed if needed within the code.

A 250 ohm resistor was placed between an analog input, a digital input and ground, this represents the VSD itself. The digital input will act as and output and will use Pulse Width Modulation (PWM) to control the voltage applied to the resistor and thus the current flow through the resistor as the resistance is static.

The code converts the desired current flow into applied voltage using the known value of the resistor and applies this voltage by sending digital pulses of either 5v or 0v where the rate defines the average voltage and thus the average current flow. The analog input then takes a live reading of the current flow or, more specifically, the voltage drop across the resistor and calculates the actual current from that. Both the selected set value of current and the actual current flow will be displayed on the LCD.