Crystal Controlled Oscillator (2023 Update)

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Why does that matter?

Jeroen Belleman

My last post was not clear. Apologies

The VCO I seek preferably produces a sine wave to reduce the part count required to filter out the higher harmonics of a square wave.

The sine wave need not be clean. There can be some raggedness to it.

It must be capable of frequencies at least within the band between

70kHz, and 80kHs. That's 70 kHz or below on the low end., and 80kHz or above on the high end.

Output voltage level, and current source limits, are not important because its output will be boosted to what is needed by a following stage.

On a sunny day (Thu, 6 Jan 2022 08:27:14 -0800) it happened Artist snipped-for-privacy@sj.gmail.com> wrote in <sr7594$ro5$ snipped-for-privacy@dont-email.me:

You will have to be more specific, but a few thoughts Those transducrs are normally capacitive, several nF, at leas the big ones I use Big ones

But I use small ones too the driving method differs!

For a sine wave, drive it with an inductor (you can, once you know C_transdcer and frequency calculate L.

opamp - L - [transducer]--- ground

Now L sets the resonance.

You will get very high voltage on the transducer for even a low drive that way, You can reduce Q by adding a series resistor for example. For a one stage you can take feedback from the transducer to an input and it will self oscillate (at value set by L). One way to go about it...

If all you want is a sinewave between 70 kHz and 80 kHz wind a coil and use this +12 coil | |--- d ---------->| JFET | | |--- s | { === | | ( | 1 n |--------0 approx sine out | ( L |--------| | ( | | | === [ ] 470 | | 2 n | /// /// ///

calculate L, wind it on some core. Note the C value ratio, could be 10 nF 20 nF etc

Won't work. The mechanical resonance dominates the response.

Cheers

Phil Hobbs

You can use the VCO in a CD4046 at (say) 8x or 16x the desired frequency into a weighted resistor "DAC" using a shift register or ring counter (I think Phil H suggested a CD4017 as one possibility).

The resulting multi-stepped near sine is very easy to filter if needed.

You could use either of the CD4046 phase comparators to servo the VCO frequency to resonance on the piezo current vs voltage, as others already suggested.

With each passing day your project looks to be getting easier and easier!

piglet

Seems to me that the op should characterize the device before speculating about things to drive it.

On a sunny day (Thu, 6 Jan 2022 12:33:48 -0500) it happened Phil Hobbs snipped-for-privacy@electrooptical.net wrote in snipped-for-privacy@electrooptical.net:

He said he uses an opamp amplifier AFTER the sine wave generator This LC oscillator circuit has been working for 50 years or more

Quite right--I read too fast.

Cheers

Phil Hobbs

On a sunny day (Thu, 6 Jan 2022 14:50:25 -0500) it happened Phil Hobbs snipped-for-privacy@electrooptical.net wrote in snipped-for-privacy@electrooptical.net:

Ok no problem, As to those small 44 kHz transducers, some here may remember the remote controls that used ultrasound (before the IR thing took over). I took one apart and had a good look a the circuit. It is just a tuned LC with the transducer capacitance part of the LC. As Phil Alison already pointed out, not much resonance in those transducers, just are big capacitors. Speakers have also resonance (usually quite low) but are driven over the full audio range or more.

So I digged in my old files

the left that transducer X1 parallel to a tunable coil (measured the inductance of it windings back then) and an other similar transducer X2 tuned with L1 as receiver into a dual gate MOSFET to make a Doppler radar. That thing was so sensitive you could detect if you blinked an eye. Here that original Philips coil and transducer from the remote: All about tuning out the transducer capacitance. Cannot seem to find the circuit diagram of the original remote, but what I used as oscillator was pretty much the same parts and circuit. It makes sense to, in stead of driving a high frequency into the transducer C, use L combined with transducer C to get electrical resonance as power consumption counts in a TV remote. There are many projects on the web that drive the transducer from say an opamp directly however.

PS did not even have to go back that far, acoustic phase wind speed meter, note the sine wave LC oscillator:

test setup. fan makes the wind: original Philips coil used bottom right.

Was all published here I am sure

Did many experiments with those transducrs:

all use the same simple LC oscillator to drive the piezo at 44 kHz IIRC or there about.

Jan, your creativity is always a source of inspiration! I'd never thought to change the inductor for a different resonant frequency.

For those who remember Gerry Coe at Devantech, he designed the now ubiquitous-on-Ebay SRF04 and SRF08 ultrasound ranging devices. These used two outputs of a MAX232 driver in push-pull to get 20V p-p drive into these transducers from a 5V supply. His other innovation was using an exponential RC decay as the reference level for the LM311 comparator, which increased sensitivity with increasing range.

I had a lot of fun with a stereo version I made, two receivers 5cm each side of one transmitter module - yielding not only range but also angular measurement to about 4 degrees. The main issue was the threshold detector, which could trigger +- one cycle, depending on whether the return impulse arrived in-phase or out-of-phase with the mechanical ring-down of the receiver. With the extra compute power that's now available, it would be possible to digitise the signal to model that ring-down, and detect the return wavefront by divergence from the model. That wasn't possible using an MC68HC11 in 1995.

Clifford Heath.

Why not a circuit similar to this self excited one used for the muRata piezoelectric microblower:

?

The op amp I would use instead is the OPA552P. It is known this has the bandwidth, and the output power, to do the job. I would, therefore, not need the buffering transistors.

To determine a compensation network I recognize I will need to characterize the piezo electric actuator either with a resistor, and a function generator, or a network analyzer if we have one. It may be that it won't need one due to there being no buffering transistors.

On a sunny day (Sat, 8 Jan 2022 09:39:26 +1100) it happened Clifford Heath snipped-for-privacy@please.net wrote in <16c81e1bd248678a$1$4060634$ snipped-for-privacy@news.thecubenet.com>:

Right, that MAX232 trick is nice! In the Philips remote the step up in that oscillator is a factor 42 (something like sqrt(8.9E-3 / 4.9E-6) from the inductance I measured of the coil. Do not remember what batteries it had, but makes sense to get a good signal from 3 V (2 x AA) or so.

I also have some ultrasonic distance meter modules from ebay, something like this:

have some special chip and a crystal. Cheap way to get transducers :-)

Now I just received some about 3 GHz? (still have to measure it) doppler motion detectors that work through glass etc. from a local shop, also for about 2 Euro a piece, on ebay those are even cheaper:

Is using that frequency even legal here? Plenty of stuff play with!

PS see

Interesting gadget. I suppose Q1 does double duty as oscillator and mixer. The schematics are of no help to figure out how it really works. Anyone care to comment? The secret is all in the PCB layout around Q1, clearly.

Also, it doesn't look like this thing could work for years on a little battery, like some PIR detectors do.

Jeroen Belleman

Pretty sure that's a version of one of Gerry's designs.

There's a bunch of new 24GHz ones too, things like this are all over AliExpress:

Clifford Heath

On a sunny day (Sat, 8 Jan 2022 22:54:49 +1100) it happened Clifford Heath snipped-for-privacy@please.net wrote in <16c84983409d8315$1$197710$ snipped-for-privacy@news.thecubenet.com>:

Thanks have bookmarked it

On a sunny day (Sat, 08 Jan 2022 11:43:11 +0100) it happened Jeroen Belleman snipped-for-privacy@nospam.please wrote in <srbprv$7t5$ snipped-for-privacy@gioia.aioe.org>:

I have a big PIR detector that was above the garden door of the old house, and would start security cams if anybody came up to the house. But it requires 12 V, and I do not want to drill a hole here and install it so want to try this one through the glass of the front door. I will get power from the PC UPS for now. But first I will experiment with it a bit!

Depending on your piezo device there could be chance of that circuit oscillating on some mode or overtone but that circuit is simple enough you could breadboard it and try inside an hour?

piglet