Author Topic: Bob Widlar's hassler circuit  (Read 10688 times)

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Offline devttys0Topic starter

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Bob Widlar's hassler circuit
« on: January 28, 2015, 03:35:36 pm »
Since Bob Widlar's infamous "hassler" circuit was never published, I thought it would be fun to design and build my own version based on the various functional descriptions floating around the internet. It's pretty simple, just uses a few op amps, but some people here might enjoy it!

There's a circuit description and demonstration video on my blog: http://www.analogzoo.com/2015/01/building-the-widlar-hassler/

Comments/suggestions welcome!
 
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Offline codeboy2k

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Re: Bob Widlar's hassler circuit
« Reply #1 on: January 28, 2015, 09:59:27 pm »
Welcome to the forum, and that was a well done video, thanks for sharing.

I watched it all the way through, and I didn't see the demonstration .

Maybe it was always on, and I'm just too old to hear 15 - 20Khz anymore :(
 

Offline dannyf

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Re: Bob Widlar's hassler circuit
« Reply #2 on: January 28, 2015, 10:46:14 pm »
Quote
There's a circuit description

U1a is a rectifier: its output goes up with the loudness sensed by the mic.

U2 is a schemitt trigger: it turns on more with louder sound;

U1b is an oscillator.

Q1/Q2 are two power AND gates.
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Offline Dongulus

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Re: Bob Widlar's hassler circuit
« Reply #3 on: January 28, 2015, 11:03:53 pm »
Now build one using a microcontroller ;)
 

Offline dannyf

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Re: Bob Widlar's hassler circuit
« Reply #4 on: January 28, 2015, 11:07:18 pm »
It shouldn't be hard:

1) configure a high-frequency pwm generator. its output to a mosfet via a resistor;
2) configure a low-frequency pwm generator. its output to the joint of the mosfet + resistor;
2) adc the input and use it to control the duty cycle of the low-frequency pwm generator;
3) done.

A 8pdip attiny should be sufficient. Or a 20 cent stm8.
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Offline Alex30

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Re: Bob Widlar's hassler circuit
« Reply #5 on: January 29, 2015, 01:08:56 am »
Really great video and well explained. Nice project too, I would be tempted to build it for a bit of quiet but I know the miss's would probably end up throwing it at the wall  :-DD
 

Offline Dongulus

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Re: Bob Widlar's hassler circuit
« Reply #6 on: January 29, 2015, 01:34:57 am »
It shouldn't be hard:

1) configure a high-frequency pwm generator. its output to a mosfet via a resistor;
2) configure a low-frequency pwm generator. its output to the joint of the mosfet + resistor;
2) adc the input and use it to control the duty cycle of the low-frequency pwm generator;
3) done.

A 8pdip attiny should be sufficient. Or a 20 cent stm8.

I kid because Bob Widlar didn't hold a high opinion of digital circuits. In fact, he probably would have smacked me for suggesting such an idea.  ;D
 

Offline devttys0Topic starter

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Re: Bob Widlar's hassler circuit
« Reply #7 on: January 29, 2015, 02:54:21 am »
I've always loved that poster of Bob Widlar, need to get one printed up for the basement lab.

Quote
Maybe it was always on, and I'm just too old to hear 15 - 20Khz anymore

That's primarily why I used a trim pot in the oscillator, I found that one of my co-workers couldn't hear a thing while the rest of us were going crazy. He's actually the youngest guy in the office too. :)

Quote
I kid because Bob Widlar didn't hold a high opinion of digital circuits.

Yeah, I didn't think he'd be too appreciative of me duplicating his work with a micro. Plus I typically have my head buried in code all day at work, so it's more interesting/fun for me to play with analog circuits when I'm tinkering around at home.
 

Offline devttys0Topic starter

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Re: Bob Widlar's hassler circuit
« Reply #8 on: January 29, 2015, 03:40:12 am »
Hmmm, I can definitely hear it in the video; maybe it's a difference in PC sound cards / speakers? It's a bit louder around 18:45 when I turn up the amplifier gain.
 

Offline codeboy2k

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Re: Bob Widlar's hassler circuit
« Reply #9 on: January 29, 2015, 07:50:44 am »
Hmmm, I can definitely hear it in the video; maybe it's a difference in PC sound cards / speakers? It's a bit louder around 18:45 when I turn up the amplifier gain.
I checked your video again, and I definitely cannot hear a single tone at 1'10 or at 18'45

Then I went to this site: http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearing-test/

From that site, I can hear everything up to 14 KHz. At 15 KHz and above that I cannot hear the tones anymore.

I am using headphones.  I do not know if this is a limitation of my headphones or soundcard audio path, etc.

Also on that page they say it's not uncommon for people over the age of 25 have difficulty hearing above 15 KHz, and I am in my 50's, so now I'm not surprised if it's there and I can't hear it :)

I guess Widlar's device only kept the noobs out.

EDIT: yes, definitely the audio path to my ears is not capable of reproducing the high frequencies.  I listened with my speakers, and at the site I mentioned above, I can only hear to 12 KHz with my speakers.

I then went to the same site with my android phone and ear buds, and I can hear all the way up to 18 KHz tone.
So my hearing is not that bad, and likely my sound system on the PC just can't go above 14 KHz or so.

« Last Edit: January 29, 2015, 08:10:23 am by codeboy2k »
 

Offline KM4FER

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Re: Bob Widlar's hassler circuit
« Reply #10 on: January 29, 2015, 04:07:45 pm »
Many years ago I started a new sysadmin job but there wasn't any work to do.  :-// 

The boss had bought me a brand new SUN workstation which was a real beauty so I spent my time messing about with it.  On either side of my cube were people who always spoke in loud voices.  It drove me crazy, I couldn't concentrate on anything, not that there was much to concentrate on.  So I wrote a program on the SUN to read the microphone input and detect high volume levels.   It didn't work very well since the mic was much more sensitive to me shuffling papers than the neighbors talking too loud.  Oh well, I learned a few things.

Three months of boredom and make work went by and I had just started to look for a different job when Management finally decided to centralize support.  For the next 15 years I was never bored nor had to find work to do.

 

Offline georges80

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Re: Bob Widlar's hassler circuit
« Reply #11 on: January 30, 2015, 01:25:23 am »
Amusing concept... More sophisticated than my high school prank.

Back in the dark ages (I was in high school, probably around grade 10) back in the early 70's....

I built an oscillator circuit and a mate & I installed it into a homemade pencil case. The bottom contained the circuit and the battery/speaker, the top had a false floor (to hide the goodies) and pencils etc sat up there. There was a microswitch that you could activate by sliding one pencil just far enough to push down on it and fire up the oscillator.

I sat at the back of the class (many knew I was an electronics nerd) and my mate at the front. He would activate the oscillator that of course was just high enough to be very irritating and non-directional due to bouncing off everything but low enough for the teacher to 'hear'.

Kids would turn to look at me, but my hands were up off the table and no link to me could be made.

I remember one class where the teacher was slowly becoming more and more irritable and some poor unfortunate student came in quite late, she totally lost it on the student who suffered her pent up wrath.

Aaah, the simpler times :)

cheers,
george.
 

Offline Asim

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Re: Bob Widlar's hassler circuit
« Reply #12 on: January 30, 2015, 09:32:04 am »
what's the current consumption of the circuit?
 I am tempted to build one as a pocket size and make it work of a battery.
 

Offline _J_Herrmann_

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Re: Bob Widlar's hassler circuit
« Reply #13 on: November 17, 2017, 07:43:20 pm »
It's true, Widlar never published his circuit, but Bob Pease did a version of his own, and published it in the May 15, 1995 issue of Electronic Design, "What's All This Hassler Stuff, Anyhow?" See attachment. I redrew Bob's hard to read handdrawn schematic in LTSpice, and added info from RadioShack about the electret mic element and piezo speaker Bob referenced in the article at the end of the pdf. I personally haven't built it yet, it's on my to do list.
 
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Offline Cyberdragon

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Re: Bob Widlar's hassler circuit
« Reply #14 on: November 17, 2017, 10:10:40 pm »
Now build one using a microcontroller ;)

NEVER

I'll use tubes instead. >:D
*BZZZZZZAAAAAP*
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Offline danadak

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Re: Bob Widlar's hassler circuit
« Reply #15 on: November 17, 2017, 11:23:46 pm »
Bob Pease article on hassler. Attached.


Regards, Dana.
Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer
 

Offline texaspyro

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Re: Bob Widlar's hassler circuit
« Reply #16 on: November 18, 2017, 05:40:26 am »
Popular Electronics Feb 1968...  "The Drip".   One of the first doo-dads I ever built.   I built one up and hid it in my 6th grade science teacher's office.  I tweaked the frequency to be rather hard to locate.  He was not amused... but then he hid it in the teacher's lounge... they were not amused.    I used an 88 mH telephone toroid for the inductor.  They used to be everywhere... you don't seem them much anymore. 
 

Offline IDEngineer

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Re: Bob Widlar's hassler circuit
« Reply #17 on: November 19, 2017, 04:51:27 pm »
I built an oscillator circuit and a mate & I installed it into a homemade pencil case.
Ah, yes. Same concept, driving an earphone (which can oscillate at surprisingly high frequencies). Right at the upper edge of most people's frequency range, the interference patterns as they moved (or even turned!) their heads made it impossible to determine location or even direction. The sound was just "everywhere".  >:D

Best deployment was at a compulsory live theater event at the school. The reactions of the nearby students and staff was a study in human psychology. The facial expressions were all over the map. Some couldn't hear it, others could, and the resulting arguments were priceless. Some got pretty intense. Other people I think weren't "hearing" it as much as just had a vague feeling of unease or annoyance. They kept suddenly turning their heads like they were going to "catch" something like an insect that was near an ear.

The best part was when we'd turn it off for a bit. Some of the arguments became hilarious. Some folks claimed "it" was still there. Others started questioning whether "it" was ever there in the first place. We soon answered that for them.  ::)

As you say... simpler times.
« Last Edit: November 19, 2017, 04:53:03 pm by IDEngineer »
 

Offline _J_Herrmann_

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Re: Bob Widlar's hassler circuit
« Reply #18 on: August 05, 2019, 03:11:22 am »
Paul Rako of Electronic Design wrote an article last year about simulating Bob Pease's Hassler circuit in Spice: https://www.electronicdesign.com/analog/what-s-all-hassler-spice-stuff-anyhow

And then wrote an article a couple of days ago about a "Shush" circuit that performs a similar function to the Hassler (this one uses some op-amps, a 555 timer and some JFETs!): https://www.electronicdesign.com/analog/what-s-all-shush-circuit-stuff-anyhow

 
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Offline vk6zgo

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Re: Bob Widlar's hassler circuit
« Reply #19 on: August 05, 2019, 04:34:36 am »
Some years back, when I worked at a place that repaired & calibrated hearing aids, one of the Techs came up with a great prank.
The bench we worked at had a top shelf held up with pieces of metal tubing.

He dropped an old hearing aid into one of these tubes.
If things were just right, the acoustic coupling between earphone & mic was not quite enough to send it into oscillation, but if you accidentally bumped the pipe, or moved something on the shelf, it would take off, squealing its heart out!

It was hard to track down where it was coming from, &, if you had just repaired a hearing aid, the obvious, but erroneous conclusion was of somrthing amiss with that aid.
(Hearing aids have a lot of gain & various problems can cause oscillation.)
 

Offline mikerj

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Re: Bob Widlar's hassler circuit
« Reply #20 on: August 05, 2019, 08:41:27 am »
I'd have thought a decent low pass filter on the input would be needed to prevent feedback latching things up?
 

Offline ArthurDent

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Re: Bob Widlar's hassler circuit
« Reply #21 on: August 05, 2019, 05:58:07 pm »
Is this the Widler poster mentioned above?

 

Offline IDEngineer

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Re: Bob Widlar's hassler circuit
« Reply #22 on: August 05, 2019, 07:29:19 pm »
One of the best posters ever - in ANY genre!
 

Online SiliconWizard

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Re: Bob Widlar's hassler circuit
« Reply #23 on: August 05, 2019, 07:48:14 pm »
It shouldn't be hard:

1) configure a high-frequency pwm generator. its output to a mosfet via a resistor;
2) configure a low-frequency pwm generator. its output to the joint of the mosfet + resistor;
2) adc the input and use it to control the duty cycle of the low-frequency pwm generator;
3) done.

A 8pdip attiny should be sufficient. Or a 20 cent stm8.

I kid because Bob Widlar didn't hold a high opinion of digital circuits. In fact, he probably would have smacked me for suggesting such an idea.  ;D

Hehe, indeed. And anyway, designing this probably took him a lot less time than it would take even an experienced programmer to implement this on an MCU. (Almost guaranteed!)
Seems simple but the devil is always in the details, and it would probably take a few hours to get it working completely and reliably on an MCU. I bet Widlar designed his hassler in like 20 minutes top. ;D
« Last Edit: August 05, 2019, 07:49:48 pm by SiliconWizard »
 

Online SiliconWizard

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Re: Bob Widlar's hassler circuit
« Reply #24 on: August 05, 2019, 07:49:20 pm »
Is this the Widler poster mentioned above?

Yes. I had it in my office a few years back. Ended up removing it because it was seen as offensive to some.
 ;D
 


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