pic16f676 Internal Oscillator frequency

[gopi90ms]

I have been working with pic16f676 .here i used adc but every time adc bit value is varying for fixed voltage.I configured adc for 4mhz frequency and I am using internal 4Mhz for that.problem is internal oscillator frequency is not stable.how to get stable 4Mhz oscillator frequency.

 

[FvM]

I think you're on the wrong track. Fluctuating ADC measurement is very unlikely related to internal oscillator frequency variations. I rather think you should study the data sheet chapter about ADC operation thoroughly. Important parameters are ADC source impedance and acquisition time setup. Lowest ADC noise will be often achieved will low ADC clock frequency and processor in sleep mode during conversion.

 

[gopi90ms]

I have tried with Led blinking also .that delay time also not same every time its varing...

 

[betwixt]

Post your schematic and software, maybe a photo of your construction too. Even the internal oscillator is very stable and certainly when divided down to make an LED flash there should be no noticable variation in speed.

I'm guessing you have something fundamentally wrong, maybe the watchdog is causing repeated resets or you have severe noise on the supply pins.

Brian.

 

[Gorgon]

If you have ADC problems I would first check the reference voltages used in the ADC.
If they are internal Vdd based only, you need to stabilize the supply voltage to a known level, or use an external reference voltage source, if possible.
Every change in the reference voltage of the ADC will change the measured value, even for a stable input signal.