The next few questions are about a circuit I worked with for my master\'s degree

Question

The next few questions are about a circuit I worked with for my master's degree (in mechanical engineering no less. So my ME and BME brothers and sisters, I feel your but I also know how many doors knowing about circuits has opened for me, and I want to be there when you get this). We had some small actuators (shown in the picture with a penny for size reference) that would get longer or shorter depending on the voltage across the ends, which we were using to create a computer controlled Braille display. Electrically, these actuators acted as capacitors (C_1 = 1 mu F), and the voltage across the capacitor changed the length of the actuator, so Delta V = 0V was fully retracted, and Delta V = 500V(!) was fully extended. These actuators were delicate, and would burn out if we ran more than 1mA of current into them. Here's a hint: you could build a similar circuit in the lab (let's replace 500V with 5) and see what happens. Use a multimeter to measure voltages at different points in the circuit as some strange things are going to happen. What is the maximum current draw from the power supply (V_s) as the digital signal from the Arduino changes from 5v to 0V? What is the purpose of resistor R_1? What is the purpose of resistor R_2?

Explanation / Answer

4) when the arduino voltage changes from 5v to 0v, gate voltage, Vg = 0, from circuit, source voltage, Vs=0

Vgs= 0. so transistor is in cut off state. therefore, maximum current, IMax = Vs/R2 = 500/1M = 0.5mA

5) Resistor R1, is used to control the value of current in actuator.

6) Resistor R2, is used to control the value of current.

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