Purpose: To use a DIP switch to switch between a mosfet tester and a ohm meter.

IO Devices used: 16x2 LCD panel, DIP Switch

Ohm Meter¶

/media/uploads/peterswanson/_scaled_resistance_final.jpg

Using the code below, the LCD screen will display the resistance and current flowing through a resistor. It was found to be accurate within about 60 Ohms.

/media/uploads/peterswanson/_scaled_resistor_network.jpg

Ohm Meter Technique:

/media/uploads/peterswanson/_scaled_ohm_meter_setup.png

• Run the 3.3V source (the red wire) through the unknown resistor (running vertical)
• Put the unknown resistor in series with another resistor (1 kOhm running horizontal) with a known value
• Connect the other end of this known resistor to ground.
• Run an analogIn(p20) from the node that is touching both the unknown resistor and the 1 kOhm resistor.

The Code for the Resistance Calculator:

 //Declarations
 AnalogIn V1(p20);
 AnalogIn V5(p17);
 //Resistance calculator
 if (DIP4 && !DIP1) {
 current = 3.3*V1/1000;
 Voltage1 = 3.3*V1;
 resistance = (3.3-Voltage1)/current;
 lcd.printf("Current is \n%.6f\n", current);
 wait(2);
 lcd.printf("Resistance is \n%4.2f\n", resistance);
 wait(2);
 }

MOSFET Tester¶

/media/uploads/peterswanson/_scaled_mosfet_display.jpg

Technique: Run the 3.3V source(with a pull-down resistor) into the Gate of the MOSFET. The AnalogOut pin is connected to the Source running 3.3V out of p18 (with a pull-down resistor). Connect an AnalogIn pin to the Drain. /media/uploads/peterswanson/_scaled_mosfet_setup.jpg

 //Declarations
AnalogOut TestVoltage(p18);
AnalogIn DSVoltage(p19);
 //MOSFET Tester
int main() {
 t.start();
 lcd.cls();
 wait(1);
 
 while(1) {
 lcd.cls();
 //MOSFET Tester
 if (DIP1 && !DIP4) {
 TestVoltage = 1.0f;
 if (DSVoltage >= 1) {
 lcd.printf("MOSFET is good!\n");
 wait(2);
 }
 else {
 lcd.printf("MOSFET no good!\n");
 wait(2);
 }
 }

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