Questions about using the A to D

[Ramius]

Hi Henrik!
Again thank you! You are correct. I connected a 10K resistor from the +5v to the ADC input pin and got 65472! Probably should have done that first! Just wondering, any way to eliminate the "bounce"?

Ed

[HenrikOlsson]

Hi Ed,

Just wondering, any way to eliminate the "bounce"?

Make sure that VRef is stable.
In this case I think you're using Vdd as Vref so proper bypassing right at the supply pin(s) of the PIC. At Vdd/VRef=5V a difference of 4.88mV will make the ADC result "jump" a LSB. So any ripple larger than +/-5mV on the supply will be reflected on the readings.

Make sure that you feed the ADC input from a low(ish) impedence circuit.
If your sensor has a high output impedence you may need to buffer the signal with a OP-amp or whatever. Filter the sensor output then feed it to the buffer then to the ADC input.

Or you can simply try throwing a 10-100nF capacitor right on the ADC input pin....
Or just filter it in software.... which, again, will allow you to oversample and get more resolution (if needed).

Remember, you're seeing a "bounce" of 4 (or 64 actually) but in reallity it's only a single LSB - and that's pretty normal.

/Henrik.