IC sine generator for 10-120khz? (re: bat detector)

[lkdurvin]

I am also interested in bats. One idea I have been wondering about was using a SDR- Software Defined Radio receiver with  attenuation at the antenna. Some models go down to 40KHz. They are not cheap, but the software will display the whole spectrum of what is coming in, and that is much better than ears. I assume it would be easy to tune it to hear the bats once you see the band. With any simple heterodyne circuit you might hear one species and miss another.
Also, frequency response of microphones is often not tested or listed past 20KHz. It my fall off, or it may not be flat at higher frequencies, yet there may be a nice signal. Some piezo tweeters are listed as reaching 40KHz. I have used a Zoom H4 digital recorder to hear bats after slowing down the recording to 1/10 speed.

 

[dfuruta]

A couple of other ideas I've found:
- a heterodyne circuit tuned by a microcontroller:  sweep until energy is detected at a particular frequency, and then stay there
- dsp or laptop based pitch-shifting
- boost & clip into a square wave -> divide-by-n counter.  One could try to reconstruct the original envelope to make it sound more intelligible.

I am thinking of having a few filters driving LEDs to indicate where something is happening in the spectrum.  This would, I think, make the heterodyne approach more usable.

I'm planning on using a mems mic intended for cell-phones - the frequency response is specified up to 80kHz, for whatever reason.  Soldering is going to be unpleasant.

The Petterson bat detector uses three microphones - two look like piezos, the third looks like a mems element.

Haven't had time recently to work on this, unfortunately.  I hope to work on it this spring...

 

[dfuruta]

An update:

I'd settled on using a triangle source -> diode breakpoint shaper -> sine;  it's cheap, relatively simple, and can be tuned over a wide range using one pot.  But, I found later that there don't seem to be relevant mixer/multiplier ICs available (everything through-hole seems to be discontinued, difficult to source, or fairly expensive).  So, I decided to do the AM modulation with a CD4066, which means the carrier has to be a square wave.  Oh well.

I'm still figuring out which mic element to use (the rest of the circuit is done), but I will post a thread about the whole thing once it's together.  Maybe it will be of interest to someone.

 

[Cjuried]

Intersil ICL8038CCPD will do .001Hz - 300kHz +. I am a fan as I use them in a few of my builds.

Hello,

Sorry if this is a little off topic.  Does anyone know of an in-production, not horribly expensive IC sine generator?  I need 10kHz-120kHz, preferably programmable with an external voltage (but an external resistance would be ok as well).  Distortion performance is not particularly important, but it needs to be a sine and not a triangle.

I am working on a simple heterodyne bat detector kit, and want it to be as cheap and easy as possible.  The XR2206 would be perfect, were it still made - as much as I can, I'd like to use parts that won't be too hard to find, and so something still active would be best.

In the interest of making this accessible to kids and people without programming ability, I'd like to keep it looking analog (of course, I don't care what's actually going on inside the chip).  If worse comes to worst, my plan is to use a microcontroller as the function generator - it would be cheap, but would add significantly to the complexity of the thing, and I don't really want to spend my time loading code onto uCs.

Any suggestions for simple, low-parts count discrete solutions will be appreciated also.

I've searched around and can't find anything, so I thought I'd ask here.

Thanks in advance for any suggestions, and my apologies if I've overlooked something in searching!

 

[dfuruta]

Out of production, as far as I can tell...

 

[Cjuried]

Yes, they are out of production. However, I have a few hundred on hand and my source bought up a good portion of the stock from Intersil. I am still comfortable, for now, using them in small to mid-size production.

 

[Cjuried]

Out of production, as far as I can tell...

Let me know if you need a few...

 

[Gene Pink]

Sorry if this is a little off topic.  Does anyone know of an in-production, not horribly expensive IC sine generator?  I need 10kHz-120kHz, preferably programmable with an external voltage (but an external resistance would be ok as well).  Distortion performance is not particularly important, but it needs to be a sine and not a triangle.

It seems to me that a down and dirty way to get a decent variable sine over the range you want, would be to beat two ring oscillators against each other.

Take a CMOS hex inverter, make two square wave oscillators up in the mhz. Make one slightly variable, run the two outputs into an AND gate, and the result should be a PWM of a sine wave that is the difference in frequency between the two ring oscillators.

LP filter, block the DC offset, and done.

Exactly how to do this is beyond my chops, but it should work in theory.

Or like a ballplayer looking to steal second, am I way off base? I don't know how stable something like this would be.

Gene

 

[JohnRoberts]

Sometimes the easiest way is the easy way....

JR

 

[Cjuried]

Hmmmm. This might be of interest.

https://www.maximintegrated.com/en/products/digital/clock-generation-distribution/silicon-crystal-oscillators/MAX038.html

and

http://www.analog.com/media/en/technical-documentation/data-sheets/AD9833.pdf

and

http://www.nteinc.com/specs/800to899/pdf/nte864.pdf

 

[dfuruta]

Gene Pink: this is interesting & I will look into it.  Thanks!

Cjuried: the maxim part is no longer made, I believe, and the AD part is teensy-tiny surface mount and needs a uC to drive it.  The NTE part looks interesting but needs 10V supply, which won't be so nice with batteries (also only goes to 100kHz, which isn't a big deal).


For now, I gave up on doing it with a sine wave for my prototype-in-progress.  Get a square from a relaxation oscillator, amplitude modulation with a CD4066, and then a low pass.  Cheap, ugly & easy.  Built a breadboard and it seems to work OK.  I'm stuck now on selecting the microphone - looking at some Knowles MEMS parts, but they're awfully small.  I'm moving like molasses, and as PRR hinted at earlier the bats will all be dead by the time I get this done...c'est la vie.

 

[Gene Pink]

Gene Pink: this is interesting & I will look into it.  Thanks!

Well, you did ask for simple. Two chips and a couple of caps and resistors. Or blow off the AND gate chip, and use two diodes and load resistor as an OR gate, just a higher output offset voltage to deal with, 12V supply means 3V offset with AND gate, 9V offset with OR gate diodes.

Ring oscillator:

https://en.wikipedia.org/wiki/Ring_oscillator

Thinking about it, you mentioned voltage controlled. Perhaps an old-school varactor/varicap after a resistor in the chain just might shift the freq of one ring oscillator about the right amount.

https://en.wikipedia.org/wiki/Varicap

PS: We don't have a shortage of bats here in Austin.

http://www.batcon.org/index.php/our-work/regions/usa-canada/protect-mega-populations/cab-intro

Gene

 

[Bo Deadly]

If you overdrive a long tailed pair curcuit with a triangle wave, you get an almost perfect sine wave. Of course the amplitude has to be just right. The long tailed pair would be just 2 transistors and 3 resistors of all the same size (like 6k8).  Ground one input and put the signal on the other. Create a simple triangle wave generator, adjust the amplitude to cause the LTP to start "clipping" and you get a sine wave on the collector(s).

 

[Cjuried]

The more I think about it, a Briged-T Oscillator might not be a bad way to go. HP used this configuration in their ULDO HP239A and HP 339A  osc. circuits. Worked out well for them...

 

[Gene Pink]

Gene Pink: this is interesting & I will look into it.  Thanks!

Don't bother, I screwed up and gave bad advice. What I suggested would give a triangle wave, not a sine.

My sincerest apologies.

Gene

 

[JohnRoberts]

In case I haven't said this before 120kHz isn't so high that you can't scale up a typical audio signal generator circuit.

Since I've gone over to the dark (digital) side, I wouldn't rule out using a cheap microprocessor.  You could use the PWM output and a lookup table to make a sine wave, for a little more you can get a dsp processor with a 16B stereo DAC built in.  I coded up a sine wave generator that makes multiple sine waves simultaneously (albeit not at 120kHz).  But a very clean 120khz sine wave is not heavy lifting.

Easy is a triangle wave with a tracking LPF or perhaps A diode break to convert triangle to sine wave, but not crazy to make an actual sine wave using modern fast op amps. 

JR

 

[Cjuried]

In case I haven't said this before 120kHz isn't so high that you can't scale up a typical audio signal generator circuit.

Since I've gone over to the dark (digital) side, I wouldn't rule out using a cheap microprocessor.  You could use the PWM output and a lookup table to make a sine wave, for a little more you can get a dsp processor with a 16B stereo DAC built in.  I coded up a sine wave generator that makes multiple sine waves simultaneously (albeit not at 120kHz).  But a very clean 120khz sine wave is not heavy lifting.

Easy is a triangle wave with a tracking LPF or perhaps A diode break to convert triangle to sine wave, but not crazy to make an actual sine wave using modern fast op amps. 

JR

Hi John,

A common practice I use with my ATMEGA168P-PU AVR series MCU's, to yield the results you note ,are as follows in this short paper: http://web.csulb.edu/~hill/ee470/Lab%202d%20-%20Sine_Wave_Generator.pdf

 

[JohnRoberts]

In case I haven't said this before 120kHz isn't so high that you can't scale up a typical audio signal generator circuit.

Since I've gone over to the dark (digital) side, I wouldn't rule out using a cheap microprocessor.  You could use the PWM output and a lookup table to make a sine wave, for a little more you can get a dsp processor with a 16B stereo DAC built in.  I coded up a sine wave generator that makes multiple sine waves simultaneously (albeit not at 120kHz).  But a very clean 120khz sine wave is not heavy lifting.

Easy is a triangle wave with a tracking LPF or perhaps A diode break to convert triangle to sine wave, but not crazy to make an actual sine wave using modern fast op amps. 

JR

Hi John,

A common practice I use with my ATMEGA168P-PU AVR series MCU's, to yield the results you note ,are as follows in this short paper: http://web.csulb.edu/~hill/ee470/Lab%202d%20-%20Sine_Wave_Generator.pdf

While I've been making sine waves for a few decades, I only started using micros this century (self taught).  My first and second generation drum tuners use PWM to sine wave for note synthesis. The first one using an 8 bit platform used two PWM outputs (one scaled down about 3 bits or so for more resolution)  feeding a 2 pole analog LPF and buffer. My second generation tuner on a 16b platform used two similar PWM outputs for the sine wave synthesis.  This time not scaled in level but phase flipped so for zero audio input, the two output square waves are opposite polarity and cancel each other out.  This trades where the errors are worst case, which for a constant sine wave doesn't buy much benefit. I feed my two PWM outputs into a class D IC with 2 poles of passive filtering. The cheap class D amp provided no external sync capability but the birdies (beats between PWM and class D) were down in the dirt and not problematic.

Of course these days with DACs built into the micros you can just output an arbitrarily pure sine wave using a look-up table. 

JR

PS: Of course I wasn't first to do this, and I saw the opposite PWM polarity trick used inside some class D amps.

 

[gyraf]

8038 kit off China: http://www.banggood.com/DIY-ICL8038-Function-Signal-Generator-Module-Sine-Square-Triangle-Wave-Output-KIT-p-1028924.html

 

[Cjuried]

8038 kit off China: http://www.banggood.com/DIY-ICL8038-Function-Signal-Generator-Module-Sine-Square-Triangle-Wave-Output-KIT-p-1028924.html

Nice little kit. Make sure that the Intersil ICL8038CCPD is authentic and not a common knockoff.