Electronic – Crystal circuit works in breadboard but not in perfboard


I'm a beginner and I'm trying to build a digital clock. My clock generator looks like this:

circuit http://img189.imageshack.us/img189/855/tempgd.png

It works perfectly on the breadboard, where I can see the LED blinking at 2 Hz. However, when I try to solder it on the perfboard, it blinks much faster. I don't have a way to measure, but I'd say something like 10 Hz.

I tried to mount three times on the breadboard and three times on the perfboard, and always get the same result. I checked and rechecked the connections, and everything seems to be fine. I have no idea where the problem might be. What could be wrong?


I tried replacing the two 15pF capacitor for two 22pF, but it didn't help. Unfortunately, I don't have access to a oscilloscope to see what's happening inside.

Here are the photos of the circuit. The first one is the component side.

photo1 http://imageshack.us/a/img405/5062/dsc07884v.jpg

The second one is the soldering side. Please excuse my bad soldering, I'm a beginner, and it's a little messy from all soldering/desoldering. However, I tested all connections and the connections are correct.

photo2 http://imageshack.us/a/img132/9470/dsc07885l.jpg

Additional question: I'm using a 10K resistor. I saw a similar circuit on the internet that uses a 220K resistor in its place. Could that be the problem?

Best Answer

Your plug type proto board adds capacitance to each node of the circuit that is greatly reduced when you attempt to duplicate the circuit onto the perf board. It is likely that the 15pF capacitors that you show on either side of the crystal may not be the correct capacitance in the perf board version of the circuit. You could try increasing the values to 18pF and then 22pF to see if either change would get your oscillator to settle down and operate at 32.768kHz as you expect it to. It may even be necessary to try 27pF or 30pF as well and it may even be necessary to use different values at each side of the crystal.