Cytron Technical Forum

lwshyang WROTE:i checked these two capacitors on board only. i have got quite weird value.
for
C5 : 170pf ( when i tune capacitance meter to 200pf range ), reversed polarity i get 1 ( too small)
1200pf (when i tune to 2000pf range), reversed polarity i get 1
C6 : 190pf (when i tune to 200pf range), reversed polarity i get 1
1400pf (when i tune to 2000pf range), reversed polarity i get 1
or can teach me how to on board measure the capacitor correctly? thanks

Thanks for the photos and video, it is very helpful for us to verify any possible problem. Seem to be the capacitor is correct. I asked this because we did get some similar cases where the board keep resetting itself and finally realize that user connect wrong capacitor at crystal. Is difficult to measure capacitance when the component is on board. That is should be fine.

Looking at the video you posted, again thanks for the effort, seem to be it is drawing too much of current at a moment and reset. After reset the current draw drop and the voltage back to normal and supply to PIC again, and this process repeat. I would suggest you to fill in the form under support tab in our website. Support team might arrange for send back and troubleshooting. That should be faster in solving your problem.

sorry that one thing that i'm not sure about it. what is the effect to microcontroller if i change the value of C5 and C6 capacitors? thanks

since i have seen some examples of oscillator's connection to PIC16F877A is using 18pF capacitors. what is the differene?

Thanks for your effort to put the image n video up! Appreciate it, really!

If you haven't send the unit to Cytron, can you check the MCLR pin of the PIC? Is it 'HIGH' or 'LOW' all the time. Like Ober mentioned, it seems like reseting itself. Sometimes I got some imperfect push buttons that shorts even without pressing them. The correct logic at the MCLR pin should be 'HIGH' for normal operation.

About your question on capacitor for the oscillator, it's stated somewhere in PIC datasheet that higher capacitance increases the stability of the oscillator, but also increases the start-up time.

Eh... according to data sheet, with 20MHz of crystal, the capacitor range form 15pF to 33pF. So if you have 18pF, you are still safe. But both cap need to have same value, else the sine wave is not symmetry.