Lesson 5--Microduino “LED Brightness and Potentiometer PWM”

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Objective In the last lesson, we used a button to generate PWM to control the LED. Now, we will use a precision potentiometer to control the LED. The difference between the two is that a button uses a digital signal (0 and 1) to control the LED. A potentiometer uses an analog signal to generate PWM which is a linear change of state, so the LED's brightness can be changed clearly and gradually. Another downside of using a button is that electronic interference can cause unintended noise. That was why we had to add a pull-up/pull down resistor to our button. Equipment Microduino-Core Microduino-FT232R Other hardware equipment 1x Box of breadboard jumper wires 1x Breadboard 1x LED 1x 220Ω resistor 1x Precision potentiometer 1x USB Data cable Experiment Schematic Connecting the Potentiometer The LED connects to any PWM output pin. The center pin of the potentiometer connects to analog ports A0 ~ A5. The potentiometer's other two pins connect to GND and 5V. The analog interface can measure 0-5V, and analogRead() returns corresponding values 0-1024. Program void setup() { pinMode(3,OUTPUT); //Choose the PWM output Port } void loop() { int val= analogRead(A0); //Read the analog port A0's value（voltage range is 0-5V,corresponding value is 0-1204） val = map(val, 0, 1023, 0, 255); //We want to map the analog value（0~1024）to（0~255) since the max PWM value is 255. analogWrite(3, val); } map() function Function: Maps a certain range of values to a different range Parameters: map(value, fromLow, fromHigh, toLow, toHigh) value: value to be mapped fromLow: Start value of source range fromHigh: End value of source range toLow: Start value of target range toHigh: End value of target range Result As you turn the potentiometer, the LED's brightness changes gradually. Video http://v.youku.com/v_show/id_XNzA5OTk1Mzky.html