Crystal Oscillator problem

[Thunderhorse312]

Hi, i'm trying to make a microcontroller work using a 16Mhz crystal oscillator connected with 2 22pF capacitors grounded. However, I was having problems with the crystal oscillator because it only works when i touch the damn thing.. Is there a problem with the circuit configration or the oscillator? how can i fix this? thanks!

 

[nandhu015]

Most of the time it happens due to improper connection. Check out for any dry soldering..

By the way what microcontroller you are using?

 

[Thunderhorse312]

Most of the time it happens due to improper connection. Check out for any dry soldering..

By the way what microcontroller you are using?

for this circuit i used PIC 16F877A. I double checked the connections, they were correct. The circuit works whenever i touch the oscillator

 

[IanP]

for this circuit i used PIC 16F877A. I double checked the connections, they were correct. The circuit works whenever i touch the oscillator

If all connections are correct ----
Not all ICs are identical, maybe this particular micro needs slightly bigger caps ..
Try 33pF ..
If this doesn't help - I think you should replace the micro ........

:wink:
IanP

 

[chuckey]

Try and find a plastic rod to tap things with (adds NO extra capacity)*. If you have a reluctant crystal, it is always well to remember that to properly match the output impedance of a chip to an input impedance, there is a big impedance transformation required. So to start of with, add more capacity to the pin that is connected to the output.
Frank
* if you attach a small piece of metal (brass) to the other end then touching a live point with this end will add extra capacity to ground. if the metal is like a little tube, then you can poke it into air cored coils to reduce their inductance as part of seing if they are truly at resonance.