2. Digital Inputs.
Below, we see the digital inputs. On the left of the diagram is a bussed 100K resistor array
attached to ground and various other points. On the right we see some op-amps wired as
comparators. These ensure that an input signal for the New, Reset or Clock input will be large
enough to get a response from the microcontroller. The inverting inputs on each of these is tied to .
05V, so any signal above .05V will turn the input on. The positive inputs of each is tied to ground
through a 100K resistor and then attached to the input jack, except for the New input, which first
goes through a diode (to protect the output of the driving circuitry from the New switch).
The outputs of these op amps each go through a diode for polarity protection, then a 100K
resistor in series with a schottky diode for overvoltage protection, and then a 100k to ground and
finally the input pin.
The digital inputs which are attached to switches, are simply connected to the bussed
resistor array and then connected to the pins of the microcontroller.
