Pierce Oscillator is "Pierceing" me off! - Page 1
Forum section: electronics / projects

author: PbFoot
author_rank: Contributor
timestamp: July 20, 2012, 09:47:59 pm
content: Hi!I am having some difficulty with what I think should be a simple problem. I have a 1 MHz xtal which I want to use with a 4060. I built up the circuit on a breadboard, using the component values specified by the xtal manufacturer. On the breadboard, it worked right away, with no troubles, even without shortening the component leads etc. It was totally stable, and very forgiving to rough construction.So, I then transferred the circuit to a protoboard, which is the type that has the same trace layout as a breadboard. Once I did this, I was unable to get the oscillator to perform correctly. The oscillator starts, but the output signal is very jittery (phase and pulse width), and the frequency varies all over the place.I did some googling, and I tried various things such as cleaning the flux from the board, tweaking component values, trying new components, making sure the leads are as short as possible. So far, I am having no luck. I can't figure it out! Maybe some capacitance from the protoboard?I read that putting the Pierce oscillator components on a separate ground plane (eg. a square of copper clad pcb) may work. Can anyone advise?Thanks!-PbFoot

author: SeanB
author_rank: Super Contributor
timestamp: July 20, 2012, 09:51:05 pm
content: Crystal case connected to gnd? Bypass capacitor on 4060 of 0.1uF with a 100uF capacitor as well.

author: amspire
author_rank: Super Contributor
timestamp: July 21, 2012, 12:41:43 am
content: In your board layout, are any of the 4060 divider output tracks running near the pin 11 track? If they are, you may have enough capacitive coupling to allow the lower frequency output to modulate to crystal oscillator a bit. You may need to add a ground track around pin 11 to help shield it.Richard.

author: PbFoot
author_rank: Contributor
timestamp: July 21, 2012, 02:16:21 am
content: Hi,I grounded the case, and added a 220uF cap across the power rails. I have put 0.1uF caps across the supply pins of the 4060 already. No change.I do have a jumper from pin 11 crossing 10 and 9. I am a bit limited with the layout on these protoboards, but I may have to look into that a bit.Any other tips or hints are much appreciated!- PbFoot

author: amspire
author_rank: Super Contributor
timestamp: July 21, 2012, 05:05:03 am
content: Quote from: PbFoot on July 21, 2012, 02:16:21 amProbably the other pins are a bigger concern.Master Reset kills the oscillator. Is the Master Reset (pin 12) connected to ground? It definitely cannot be left floating.Also, when you see the jitter, are you looking at pin 9 or pin 10? Probably want to look at pin 9, or even better, pin 7.Richard.

author: vk6zgo
author_rank: Super Contributor
timestamp: July 21, 2012, 10:57:29 am
content: Disconnect everything that isn't to do with the oscillator,& see if it's still unstable.If so,if you still have the original "spiderweb"circuit,put the crystal back in & see if it still works there.If it is unstable there,you probably have a faulty crystal.You should be able to build 1MHz crystal oscillators with a minimum of fuss----after all,it's not rocket science!

author: PbFoot
author_rank: Contributor
timestamp: July 24, 2012, 02:23:42 am
content: Thanks for all the hints! Turns out my resistor was too big, and the xtal was just on the edge of starting, but not quite. I deleted the resistor and it works perfectly now, without a hint of a problem. Strange thing is that it worked on the solderless breadboard with that resistor in, so I never considered it to be the problem.- PbFoot