How accurate is the internal oscillator ?

[rsocor01]

lilimike,

For example, a PIC18F4550 has a +/- 2% internal frequency variation at room temperature (25 deg. C). This is according to the datasheet, electrical characteristics section. However, these chips are calibrated in the factory and the 2% is just the worst case scenario. The accuracy in frequency is ussually pretty good.

A typical 4MHz crystal can have a frequency tolerance of +/- 30 ppm at room temperature. This is equivalent to +/- 0.003% in frequency variation.

For the type of application that you want, the internal oscillator should be good enough.

Robert

[lilimike]

I am using a 16F628A.
I did see the datasheet but I was not sure exactly how to interpret it.

Even with temperature change as long as there is no drastic change within a few seconds I should still be ok.

Thank you for the information.

Mike

[rsocor01]

The next sentence is from the 16F628A datasheet page 1.

Precision internal 4 MHz oscillator factory
calibrated to ±1%

Check page 153 of the datasheet for the graph "TYPICAL INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE, VDD = 5 VOLTS".

Robert

[lilimike]

yes I see, looking at the graph is more clear.

Thank you