Electronic – How to stablize an analog to digital reading

I found out the problem was that my reference was not set correctly in the OpenADC() function. I needed ADC_REF_VDD_VSS instead of ADC_VREFPLUS_VDD. Here is the correct way to read an A/D value. This part goes inside the while(1) loop shown in the question.

// Constraints: A/D acquisition time must be >= 2.4 us (data sheet p264, Equation 20-3), conversion time (Tad) must be >= 0.7 us (data sheet p385, Table 26-26)
// Given that our Fosc = 4 MHz, which means Tosc = 1/Fosc = 1/4 MHz = 0.25 us,
// we must have at least 4 * Tosc = 1 us of conversion time (Tad).
// This is why we choose ADC_FOSC_4.
// Since Tad = 1 us, and we need a minimum acquisition time of of 2.4 us,
// we choose acquisition time to be 4 * Tad, which is ADC_4_TAD
// Use channel 0 (ADC_CH0) to read AN0
OpenADC(ADC_FOSC_4 & ADC_RIGHT_JUST & ADC_4_TAD, ADC_CH0 & ADC_INT_OFF & ADC_REF_VDD_VSS, 0);
Delay10TCYx( 5 );        // allow for time to open adc (don't know if need this much)
ConvertADC();            // initiate conversion of sensor1 @ AN0
while(BusyADC());        // waiting to complete conversion
myVoltage = ReadADC();  // read A/D value. math needs to be done to convert to voltage
CloseADC();

I'd say that is a classic task for comparators.

^{simulate this circuit – Schematic created using CircuitLab}

Note that the resistors don't have the correct values you need, you will have to calculate them according to your needs.

Comparators will output "1" (supply voltage) if the + voltage is higher than the - voltage. Otherwise they will output "0".

So for this task you will need 2 comparators, one configured to look if the output is lower than V1, that's CMP1. And one that looks if the voltage is higher than V2, that's CMP2s job.

With the potentiometers you can vary the voltages V1 and V2.

For a task like that, I'd also use a hysteresis as signal outputs tend to be noisy and you probably don't want that near the voltage V1 or V2 the signal trips often because it's varying slightly around that point. So basically the hysteresis will serve as a debouncing.

There are comparators available which have a built in hysteresis, but you can add one with using just resistors to any comparator.

Using just transistors and resistors, you might as well be able to do that, but I'm really not good at those levels of electronics.