Keyboard with Analog Output
by Wagner Lipnharski - 1992
This diagram is
along with the equipment it makes part, for UST Research Inc.
You can use it only at your own personal electronics,
not for commercial projects
This circuit allows you to connect a keyboard using only three wires
from the microcontroller, Ground, +5Vdc and the Return Analog signal.
If your microcontroller has an analog input, it is easy,
since the resolution of this circuit is 14mV.
You can use any voltage at the +Vdc pin, but for +5Vdc here
goes the table for pressed keys and output voltage generated:
Switch is pressed if
the output is more
If voltage at output is less than 70mV, no switch is pressed,
easy to read and to compare with a capacitor charge.
All resistors need to be 1% 1/8 Watt - Metalfilm.
A matrix 4 x 4 can be built, but first grab a calculator and
the list of regular resistor values on the market.
Bigger matrix combinations require an ADC circuit with
better resolution. This one works with only 8 bits ADC's.
Unpredictable results can happens with multiple key pressed.
Good luck and Have fun,
Wagner Lipnharski, October 1992.
posted at internet at feb.1999
Copyright (C) UST Research Inc. 1992 - Equipment - Portable pH & ORP calibrator.
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