Quartz crystals

[hilbert42]

The article is a nostalgic reminder of when I was first interested in electronics and got interested in quartz resonators for projects. Grinding down old war surplus FT243-style crystals and other types so as to resonate at frequencies I needed was a common practice with hobbyists back then.

I used many similar techniques to the same end of removing quartz which raised its frequency. Grinding materials included abrasives such as jeweler's rouge, cerium oxide, commercial polishes such as Brasso and Silvo and even HF solution. I'd place the quartz on a small section of plate glass and slide it through a slurry of the abrasive periodically testing its frequency until I'd reached my target.

There's an art to this that's too long to mention here except to say abrasives were used strategically, course grinding would get me near the desired frequency and I'd finish off with a fine abrasive. Then there was the job of re-aging the crystal after its recent abuse to increase its stability. Other techniques were involved such as not lowering its Q factor, etc. which I'll not cover here.

The most desired crystal cut was from the XT-plane (being the most stable) but it was generally difficult to get as it's only a small section of the quartz crystal (also each cut oscillates only over a limited range of frequencies). I used to have a book that explained these cuts in detail, their frequency ranges and electronic properties along with the basic crystallography which I lost years ago. A quick glance at the book would have shown that a great deal of science, engineering and skill is involved in the selection of quartz and its manufacture into useful resonators.

BTW, the mentioning of HF will likely horrify chem-phobic readers. We were well aware of its dangers and took special precautions never to come in contact with it.

[gilleain]

> BTW, the mentioning of HF will likely horrify chem-phobic readers I would not say I am chem-phobic, but yes indeed that stood out. HF is nasty stuff, and yes requires some care I suspect.

The other details are fascinating, though - the intersection of mechanical, crystallographic, and RF (?) properties of a crystal that you can adjust through abrasives and selection of the cut.

[gtsnexp]

This awesome. Could you perhaps remember the title of the book you lost?

[vincnetas]

So is this art of selecting right crystals is applicable for synthetic crystals also or these can be grown perfect each time to specifications?

[hilbert42]

Heavens, that should be AT cut not XT. What on earth was I thinking of?

Some of you guys should have picked that up. ;-)

[jacquesm]

That sinking feeling of knowing you've ground off just a bit too much...

[tomcam]

> according to [2] a train crashed in 1972 due to a badly designed crystal oscillator spontaneously jumping to its third overtone

New fear unlocked

[jacquesm]

More interesting: amazing sleuthing to figure out that that was the root cause.

[pfdietz]

I remember when I worked at Motorola some decades ago, there was a little section in the factory area in Schaumburg that made quartz crystals. It's all long since been sold off (I think all the equipment went to China) but I remember all the signs for cyanide alarms, presumably due to some step in the manufacturing process.

The quartz crystals themselves were grown with carefully controlled levels of specific impurities (like scandium) in order to reduce their temperature sensitivity.

[adrian_b]

They may have had baths for galvanic deposition of silver. Those typically used cyanide solutions.

Galvanic deposition of silver has been frequently used for increasing the thickness of thin metal layers that had been deposited in vacuum, in order to adhere to the crystal.

[sbinnee]

Believe or not, when I explained to many non techies how quartz watches work and how any computers’ hardware clocks work in the same principle, they were all surprised how elegant and how efficient the mechanism is. I was also impressed when I first learned about it. True science and engineering beauty.

[jacquesm]

Have a look at the company Silicon Time, they make the most amazing little devices.

[jacquesm]

Nice to see this get more love, I had a fun time going through that site, there are lots of gems there.

For instance:

https://www.pa3fwm.nl/projects/sdr/

The longer you read, the more amazed you will be.

[jadbox]

Dang that fascinating but way above my head. I need to take a few classes in signal processing I think to parse what's all going on here.

[zeofig]

The account of the youtube video linked in the article has been terminated apparently. Anyone know why or if there's an alternate link?

[maxbond]

https://web.archive.org/web/20160422054642/https://www.youtu...

[speakspokespok]

With a crystal of the right dimensions and correct input voltage could one feel the crystal vibrating?

[s0rce]

There are piezo actuators you could certainly feel but not sure they are made of quartz, maybe PZT.

[Isamu]

You mean could you get it down to a low enough frequency? Hmm I guess you can get down into audio frequency but maybe the amplitude will be tiny, you probably want a piezo mechanism that will give you more of a rumble.

[gosub100]

And a similar question: if you took a normal magnet and rotated it very quickly, say 10k rpm, would it emit an RF signal at (10k/60) hz? I'm 95% sure the answer is yes but I've never seen this demonstrated.

[intrasight]

Nice. I'm an EE by education. We weren't taught how such a key piece of the puzzle worked.

[amelius]

Could someone take the equivalent circuit of the article and put in in CircuitJs to form an oscillator? Thanks!

[dilawar]

Obligatory: https://youtu.be/wHenisSTUQY?si=oNOHR9QRCG3GYvf2

[dilawar]

Just realised this video is referenced in the article! Didn't read it carefully.

[Simboo]

Now that was nice. I liked that a lot thank you for sharing.