A 1-Wire Keyboard (or analog keyboard) Calculator (1-Wire Keyboard) is a tool for embedded system designers to implement a keyboard or keypad using a single analog-to-digital converter (A/D) input. For larger keyboards, or keypads that require chording (more than one key pressed at a time) multiple A/D inputs can be used, each with a portion of your complete keypad.
1-Wire Keyboard supports from two (2) to 64 key keyboards; however, keyboards beyond 26 keys may be hard to realize with a single A/D input and low cost resistors. 1-Wire keyboards offer lower EMI than scanned keyboards, need fewer ESD protection components to implement, and also only require one pin on a microcontroller.
If minimizing current consumption is a concern and the current drain of long key presses cannot be tolerated, the keypad ground can be replaced with a second pin on the microcontroller configured as an open drain output. When reading a key this pin should be set to output a zero. The software can protect against excessively long key presses by allowing that pin to float (input mode, no pull down), just add this pin’s pull down resistance to your contact resistance value.
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