wiring a 32.768 khz crystal resonator

Thread Starter

Green Bean

Joined Mar 31, 2017
126
I have just got 5 of these in the mail. I'd like to make a 32.768 khz crystal oscillator, and it looks like I have to wire the resonator to some resistors and capacitors. My question is, if I don't have resistors/capacitors with the correct values (which I don't), is there any reason I can't connect them in combinations of paralell and series to get the resistance and capacitance I need?
 

ian field

Joined Oct 27, 2012
6,536
I have just got 5 of these in the mail. I'd like to make a 32.768 khz crystal oscillator, and it looks like I have to wire the resonator to some resistors and capacitors. My question is, if I don't have resistors/capacitors with the correct values (which I don't), is there any reason I can't connect them in combinations of paralell and series to get the resistance and capacitance I need?
Most manufacturers publish a catalogue with a few pages of sample circuits at the back. Murata springs to mind, but they're not alone.
 

MaxHeadRoom

Joined Jul 18, 2013
28,576
If these are 4 pin they are usually self contained oscillators and usually just need power and common and one output and possibly an enable for the fourth pin.
Max.
 

EM Fields

Joined Jun 8, 2016
583
I have just got 5 of these in the mail. I'd like to make a 32.768 khz crystal oscillator, and it looks like I have to wire the resonator to some resistors and capacitors. My question is, if I don't have resistors/capacitors with the correct values (which I don't), is there any reason I can't connect them in combinations of paralell and series to get the resistance and capacitance I need?
In a word, "No."
 

Thread Starter

Green Bean

Joined Mar 31, 2017
126
Manufacturer / part number / photo -- anything.

ak
Yes, sorry sorry! I didn't have a lot of time when I posted this and I've been gone all day. I've attached photos of the receipt (I think it's a receipt) and one of the resonators on a breadboard. The seller is EchoTech solutions. 3 of the resonators say "S033" and the other 2 say "S013" but they are otherwise identical. Searching "S033 crystal resonator" or "S013 crystal resonator" doesn't produce any results, so I don't think those are part numbers.

That's all the info I have.

However:
In a word, "No."
I've been learning about wiring resistors and capacitors in parallel and series to get resistances and capacitances that I need for circuits without using resistors or capacitors with the specific resistances and capacitances required. I'll wait while you read that 4 more times. :)

But, I'm also starting to learn that the byproducts of using these techniques can cause other problems, so it doesn't always work exactly as it should (or at least exactly as I think it will, lol).

So now, with the information I have provided (which is admittedly meager, but all I could find), will a crystal oscillator circuit like the one in the schematic I've included (which is attached to what is basically a frequency divider) still work EVEN if instead of using resistors and capacitors with the listed values, I use a combination of resistors and capacitors that I actually have here in my little lab, in series/parallel/whatever, to get the listed resistances and capacitances? It looks like the answer is generally "sure" but maybe my resonators are special (I don't know lol).

IMG_20170702_2101383_rewind.jpg IMG_20170702_2102473_rewind.jpg th (25).jpg
 
Last edited:

MrChips

Joined Oct 2, 2009
30,620
The circuit you have posted calls for:

470KΩ
10MΩ
10pF
22pF

Tell us what you have that is the closest, both below and above.
Then tell us what you will substitute in order to meet those values.

We will guide you from there.
 

AnalogKid

Joined Aug 1, 2013
10,971
First. that is a crystal, not a complete oscillator device. Second, technically, it is a tuning fork resonator, not a traditional crystal (which would be much larger for the same frequency). It thinks like a crystal, and your schematic should work with it.

ak
 

Alec_t

Joined Sep 17, 2013
14,263
You'll hopefully get away with combining Rs/Cs, but such combinations introduce parasitic inductance and capacitance which may have undesired effects on stability/frequency.
 

ian field

Joined Oct 27, 2012
6,536
First. that is a crystal, not a complete oscillator device. Second, technically, it is a tuning fork resonator, not a traditional crystal (which would be much larger for the same frequency). It thinks like a crystal, and your schematic should work with it.

ak
Looks like a regular watch "crystal" - its an abundant resource and there's plenty examples online.
 

Thread Starter

Green Bean

Joined Mar 31, 2017
126
The circuit you have posted calls for:

470KΩ
10MΩ
10pF
22pF

Tell us what you have that is the closest, both below and above.
Then tell us what you will substitute in order to meet those values.

We will guide you from there.
Ok, well I do have 470 KΩ resistors and 22 pF capacitors. Two of them in series would give me 11 pF, is that close enough to 10 pF to work? I also have some 1 MΩ and 10 Ω resistors, one of each in paralell would give me 10MΩ.

You'll hopefully get away with combining Rs/Cs, but such combinations introduce parasitic inductance and capacitance which may have undesired effects on stability/frequency.
Yes, that's what I was afraid of.
 

Thread Starter

Green Bean

Joined Mar 31, 2017
126
Hmm. Work through your math again.
Ok.
I also have some 1 MΩ and 10 Ω resistors, one of each in paralell would give me 10MΩ.
Alright, it looks like I'd need ten 1 MΩ resistors to get 10 MΩ (I think that's it). Oops lol. But it looks like I'll just have to get resistors and capacitors with exact values, because, as Alec_t pointed out:
You'll hopefully get away with combining Rs/Cs, but such combinations introduce parasitic inductance and capacitance which may have undesired effects on stability/frequency.
 
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