low-cost keyboard

Posted on Jul 6, 2012

If your application uses a relatively powerful microcontroller, you can use several free I/O pins or an unused input with an ADC to effect an easy keyboard connection. But, if the microcontroller in your system has too few free I/O pins and no on-chip ADC, you can be in trouble. However, if your system doesn`t require a high-performance keyboard, you can solve the problem by using the circuit in Figure 1.

I/O (output) assumes the state logic 1, VOUT. VC charges to logic 1 (VOUT) or to a voltage that RS and the other resistors determines. (You can set the output I/O to logic 1 by default. In this case, you can omit steps 1 and 2, and the routine becomes f

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