ANALOG KEYBOARD

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Figure 1. Analog Keyboard resistor key matrix

Figure 2. Multiple key press

PRINCIPLE OF OPERATION

The combination of the pull-up resistor, the serial resistors and the pressed key form a resistive

voltage divider, generating a different voltage at the ADC input for each key pressed. The serial

each switch combination to give the best noise margin between keys.

When a key is pressed, the voltage at the ADC input is given by the activated voltage divider.

This analog voltage is converted by the ADC and the digital value is used to determine which

switch is closed. Two successive conversions may be made to avoid the influence of key bounce.

If the top key is pressed, the voltage measured is always zero. For n keys, the resistor values should