# Lesson 1--Microduino Resistor Meter

 Language: English  • 中文

## Objective

This lesson will teach you how to use Microduino to make a resistance meter. The basic principle is that use the reference resistor, comparing the voltage, then calculate the resistance value. Through testing, using 20k as the base, if the resistance value more than 1k, the result more accurate.

## Equipment

• Microduino-Core
• Microduino-FT232R
• Other hardware equipment
• 20kΩ resistor one
• 104 ceramic capacitor one
• USB Data cable one

Capacitor

brief introduction：

Ceramics is qualitative, 104 is three digits notation, the former two significant figures, the next one is the number of 0. 104 means it is 100000PF, equal to 0.1 uF. Commonly used as bypass capacitor in high frequency or low frequency circuit, and commonly used in power supply decoupling, also has a coupling effect.

## Schematic

You can change the reference resistor according the measure scope, in order to get a good accurate.

Circuit Connection:(Using 104 ceramic capacitor)：

## Program

```    #define N 12
#define basis 20000.0   //Reference resistor

int potpin = A4;
float val, r;

void setup()
{
Serial.begin(9600);
}

void loop()
{
r = ((basis * 1023.0) / (1023.0 - val)) - basis;
delay(100);
Serial.print(" R:  ");
if(filter() >= 1000)
{
if(filter() >= 500.0*1000.0)
{
Serial.println("Infinity!!");
}
else
{
Serial.print(filter() / 1000.0);
Serial.println("K ohm");
}
}

else
{
Serial.print(filter());
Serial.println(" ohm");
}
}

//Filtering algorithm, use the average filtering algorithm
float filter()
{
float sum = 0;
for(int count = 0; count < N; count++)
{
sum += r;
delay(5);
}
return (float)(sum / N);
}```

## Debug

Step 1: Copy the code to IDE, and compile it

Step 2: Connect the circuit, as follows:

In figure, the upper resistor is 20k reference resistor, and the low registor is the measured one.

Step 3: Run program

Step 4: As figure shows, put the yellow line and black line to both end of the resistance, serial will show the resistance value.

You also can change to other object to test the resistance, such as soap, a damp cloth and so on.

## Result

Serial will show the resistance value.