[–] ExpertShitposter 0 points 3 points (+3|-0) ago  (edited ago)

Its more than that. The crystal will not function correctly or at all without them even if there is no noise in the circuit. And since it is responsible for the clock of your Micro controller, if that is skewed then everything else will be as well.

Just use whatever the chip manufacturer recommends.

[–] uvb76 [S] 0 points 1 points (+1|-0) ago 

Thanks but the board is already in production. I just wondered why they were there.

What do they do for the crystal that make the square wave?

[–] ExpertShitposter 0 points 1 points (+1|-0) ago  (edited ago)

Its been a long time since i read up on specifics of that, but you can google it.

[–] EvilSeagull 0 points 3 points (+3|-0) ago 

Could this be an oscillator circuit? The capacitors are to make the clocking work.

[–] uvb76 [S] 0 points 2 points (+2|-0) ago 

The crystal is making the pulse for the IC. The full board is a phenumatic control module. I can't show it; it's not mine. I'm just curious about the use of the capacitors on both sides of the crystal.

So you're saying that the capacitors are required to make the square pulse?

[–] varialus 0 points 2 points (+2|-0) ago 

Nobody told me y'all be workin' with honest to goodness crystals that are practically doing magic shit! Fuck crystals for spiritual aura nonsense, I gotta learn me some electrical engineering. Electricity doesn't make any damn sense to me. If there were real magic in the world I'd no doubt be missing out because it'd probably be as stupid confusing as electronics. But bless y'all for learning it, cuz I ain't got the temperament for it.

[–] AmaleksHairyAss 0 points 1 points (+1|-0) ago 

I gotta learn

I ain't got the temperament for it.

Choose one.

[–] varialus 0 points 1 points (+1|-0) ago 

The latter. The former is but a whim of a wish.

[–] nignognoose 0 points 2 points (+2|-0) ago 

Capacitors store up the crystal's energy for a more powerful release?

[–] uvb76 [S] 0 points 1 points (+1|-0) ago 

It might help more to know what the capacitive value of the parts in question. They were ceramic 0603 so no value code. Just wondering if it was for keeping the clock pulse clean. Anmanlndusties suggested that it might be to protect from voltage drops.

[–] AnmanIndustries 0 points 2 points (+2|-0) ago 

I dont know if relevant, but I remember having to put in capacitors to prevent energy drops. In the project there were additional devices afterwards that also had the same requirement so another capacitor was added after the first device.

[–] uvb76 [S] 0 points 1 points (+1|-0) ago 

Like a pull up capacitor? I've read the term but not sure on the details, I'm self taught and probably missing foundational info. This board is very dense with components and microcontrollers so protection on voltage drop makes sense. It's some type of phenumatic controler.

[–] AnmanIndustries 0 points 2 points (+2|-0) ago 

Honestly, no idea. Im very much out of the electrical scene.

[–] uvb76 [S] 0 points 1 points (+1|-0) ago 

@TheBuddha ? If you care to comment.

[–] TheBuddha 0 points 1 points (+1|-0) ago 

My last EE classes were in 1983 and I've not kept up. Basically, because the phases aren't going to be exact in practice.

Here's an answer that dances around it - and seems to match my memory:


The key phrases would be:

In practice the two ends of the crystal don't oscillate quite 180 degrees apart, and the capacitors aren't sized to match the amplitude ratio,

Again, it's been a whole lot of years. I dropped my minor in EE and swapped from Pure Math to Applied Mathematics for grad school. I just couldn't handle going for a doctorate in both - so those skills have lain by the wayside. I absolutely encourage you to double check and doubt my answer. That should give you a head start.

[–] uvb76 [S] 0 points 1 points (+1|-0) ago 

Thanks for the reply. This seems in line with what expertshitposter said. I was just curious if there was a short answer and it seems that they are just necessary for the oscillation. After I had pinged you I looked at another board we were building and it was set up the same way. Thanks for the link too, I'm reading up on that now.

[–] littul_kitton 0 points 1 points (+1|-0) ago 

I'll start by assuming this is an oscillator, although it is not drawn that way.

The crystal manufacturer calibrates its frequency with a certain capacitance attached to both terminals. If you use it with that capacitance attached, the frequency is more accurate. The PCB designer then looks up or measures the capacitance of the IC pins, subtracts that from the specified capacitance, and adds capacitors to make up the difference. In practice almost nobody cares about the exact frequency, so the capacitors are chosen more by voodoo than engineering.

[–] uvb76 [S] 0 points 0 points (+0|-0) ago 

It's kind of funny how some of this stuff works. We have been working on these "low cost" USB power supplies and they have been in and out of rework for various reasons. The new fix now is to attach a daughter board to the bottom with 2 resistors and a SOT23. I can not tell what this is doing because I've tested one without this mod and it outputs the same. Guess there just throwing science at the wall.

Thanks for the reply. I'll read the data sheet for that part and see what it says. Never really looked at the data sheet fro crystals.

[–] k_digi 0 points 1 points (+1|-0) ago 

that's a great question.

  • i don't have a definitive answer. and if i did it would be in froopy non human language anyhow, as i don't understand backwards 'electronics'

but thanks for asking it.

[–] uvb76 [S] 0 points 0 points (+0|-0) ago 

No problem.

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