If you getting tired of using the ordinary touchable keyboard, which is require the users to enter the password one after one number, then it’s time for you to test out the AVR-Based Sensor Keyboard.
For your information, the AVR-Based Sensor Keyboard is definitely a wonderful device, as it’s built based on a modern microcontroller. Honestly, it has almost everything, which is needed to implement a touch sensor matrix.
The concept that being used for the AVR-Based Sensor Keyboard is based on the QMatrix Technology White Paper. The main goal is to transfer the charge through the sensor capacitance to a tank capacitor, until a charge sufficiently large to be measured builds up.
Then, a current will be applied to the tank capacitor. The time that it takes to reach zero crossing is measured as well. In this case, when sensor surface is being touched, the sensor is going to detect the user and verify the identity of the user instantly.
By the way, you might want to choose an ATMega8 as the test platform. Also, please pay attention on the builtin analog comparator, as it’s the most important components to detect the moment of zero crossing accurately!