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This board provides you the most ideal solution to add a keypad by using least number of I/O pins in your DIY projects. You can have 16 buttons ordered 4x4 by connecting this one analog voltage out board to one of ADC pins of your microcontroller.
Each one of the buttons pressed provides different boltage levels with the different resistors connected to theem. You can calculate this voltage with this simple formula:
Vo = [(button index/16) x Vref] ± %6
For example: When the board is operating with a 5 V Arduino board, if th button 8 is pressed, the output becomes Vo = (8/16) x 5 V = 2,5 V . If we give this voltage to one of the analog input pins of arduino, as the ADC modul of arduino is 10 bits, (2^10 = 1024) 2.5 / 5 x 1024 = 512 will be red. There is %6 error rate based on the tolerances of the resistors.