The bar graph – a series of LEDs in a line, such as you see on an audio display – is a common hardware display for analog sensors.
It’s made up of a series of LEDs in a row, an analog input like a potentiometer, and a little code in between. You can buy multi-LED bar graph displays fairly cheaply, like this one. This tutorial demonstrates how to control a series of LEDs in a row, but can be applied to any series of digital outputs.
The sketch works like this: first you read the input. You map the input value to the output range, in this case ten LEDs. Then you set up a for loop to iterate over the outputs. If the output’s number in the series is lower than the mapped input range, you turn it on. If not, you turn it off.
/* LED bar graph Turns on a series of LEDs based on the value of an analog sensor. This is a simple way to make a bar graph display. Though this graph uses 10 LEDs, you can use any number by changing the LED count and the pins in the array. This method can be used to control any series of digital outputs that depends on an analog input. The circuit: * LEDs from pins 2 through 11 to ground created 4 Sep 2010 by Tom Igoe This example code is in the public domain. http://www.arduino.cc/en/Tutorial/BarGraph */
For more detail: Arduino LED Bar Graph Code
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