Member #481555

Member Since: October 23, 2013

Country: United States

  • Product COM-08653 | about 6 months ago

    A problem with the R-ladder is that with no button pressed, the “idle voltage” is too near one of the actual “key voltages”. So, here’s another approach.

    Given the narrow spread between voltages, I’ve opted for using 1% resistors for this. They are available at Mouser.

    Hookup: Connect a 27.4K resistor from pad 3 to GND Connect pad 3 to pad 1 with a 60.4K resistor Connect pad 1 to pad 5 with a 210K resistor Connect a 309K resistor from pad 2 to V+ Connect a 154K resistor from pad 7 to V+ Connect a 66.5K resistor from pad 6 to V+ Connect a 10.0K resistor from pad 4 to V+ Connect pad 3 to an analog input on the Arduino (or any 1024-bit ADC)

    With this, the expected digital readings for the various keys are:

    1: 82 ~ 85 4: 152 ~ 157 2: 223 ~ 230 7: 295 ~ 303 5: 367 ~ 377 3: 497 ~ 509 8: 576 ~ 590 6: 667 ~ 683 *: 742 ~ 759 9: 828 ~ 846 0: 909 ~ 929

    : 980 ~ 1002

    with a reading of zero if no key is pressed. The minimum gap between any two key reading ranges is 51.

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