View source for Lesson 1--Microduino resistance Meter

{{Language|第一课--Microduino 电阻计}}

==Objective==

This lesson will teach you how to use Microduin to make a resistance meter. The basic principle is that use the reference resistor, compareing 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
**Breadboard Jumper            one box   
**Breadboard  	               one piece  
**20kΩ resistor 	             one 
**104 ceramic capacitor        one  
**USB Data cable               one

'''Capacitor'''
[[File:第一课-电容.jpg|600px|center|thumb]]

'''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)：

[[File:第一课-Microduino电阻计原理图.jpg|600px|center|thumb]]

==Program==
<source lang="cpp">

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

    int potpin = A4;
    float val, r;

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

    void loop()
    {
        val = analogRead(potpin);
        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);
    }

</source>


==Debug==

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

Step 2：Connect the circuit, as follows：
[[File:第一课-Microduino电阻计连接图.jpg|600px|center|thumb]]
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.

[[File:第一课-Microduino电阻计串口显示电阻值.jpg|600px|center|thumb]]

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.
==Video==
http://v.youku.com/v_show/id_XNjc3MzU3ODIw.html