Bob Widlar's hassler circuit - Page 1
Forum section: electronics / projects

author: devttys0
author_rank: Contributor
timestamp: January 28, 2015, 03:35:36 pm
content: 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!

author: codeboy2k
author_rank: Super Contributor
timestamp: January 28, 2015, 09:59:27 pm
content: 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

author: dannyf
author_rank: Super Contributor
timestamp: January 28, 2015, 10:46:14 pm
content: QuoteU1a 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.

author: Dongulus
author_rank: Regular Contributor
timestamp: January 28, 2015, 11:03:53 pm
content: Now build one using a microcontroller

author: dannyf
author_rank: Super Contributor
timestamp: January 28, 2015, 11:07:18 pm
content: 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.

author: Alex30
author_rank: Regular Contributor
timestamp: January 29, 2015, 01:08:56 am
content: 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

author: Dongulus
author_rank: Regular Contributor
timestamp: January 29, 2015, 01:34:57 am
content: Quote from: dannyf on January 28, 2015, 11:07:18 pmI 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.

author: devttys0
author_rank: Contributor
timestamp: January 29, 2015, 02:54:21 am
content: I've always loved that poster of Bob Widlar, need to get one printed up for the basement lab.QuoteThat'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.QuoteYeah, 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.

author: devttys0
author_rank: Contributor
timestamp: January 29, 2015, 03:40:12 am
content: 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.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 29, 2015, 07:50:44 am
content: Quote from: devttys0 on January 29, 2015, 03:40:12 amI checked your video again, and I definitely cannot hear a single tone at 1'10 or at 18'45Then 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 itI 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.

author: KM4FER
author_rank: Regular Contributor
timestamp: January 29, 2015, 04:07:45 pm
content: 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 whoalwaysspoke 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.

author: georges80
author_rank: Frequent Contributor
timestamp: January 30, 2015, 01:25:23 am
content: 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 timescheers,george.

author: Asim
author_rank: Regular Contributor
timestamp: January 30, 2015, 09:32:04 am
content: 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.

author: _J_Herrmann_
author_rank: Newbie
timestamp: November 17, 2017, 07:43:20 pm
content: 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.

author: Cyberdragon
author_rank: Super Contributor
timestamp: November 17, 2017, 10:10:40 pm
content: Quote from: Dongulus on January 28, 2015, 11:03:53 pmNEVERI'll use tubes instead.

author: danadak
author_rank: Super Contributor
timestamp: November 17, 2017, 11:23:46 pm
content: Bob Pease article on hassler. Attached.Regards, Dana.

author: texaspyro
author_rank: Super Contributor
timestamp: November 18, 2017, 05:40:26 am
content: 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.

author: IDEngineer
author_rank: Super Contributor
timestamp: November 19, 2017, 04:51:27 pm
content: Quote from: georges80 on January 30, 2015, 01:25:23 amAh, 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".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.

author: _J_Herrmann_
author_rank: Newbie
timestamp: August 05, 2019, 03:11:22 am
content: 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-anyhowAnd 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

author: vk6zgo
author_rank: Super Contributor
timestamp: August 05, 2019, 04:34:36 am
content: 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.)

author: mikerj
author_rank: Super Contributor
timestamp: August 05, 2019, 08:41:27 am
content: I'd have thought a decent low pass filter on the input would be needed to prevent feedback latching things up?

author: ArthurDent
author_rank: Super Contributor
timestamp: August 05, 2019, 05:58:07 pm
content: Is this the Widler poster mentioned above?

author: IDEngineer
author_rank: Super Contributor
timestamp: August 05, 2019, 07:29:19 pm
content: One of the best posters ever - in ANY genre!

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 05, 2019, 07:48:14 pm
content: Quote from: Dongulus on January 29, 2015, 01:34:57 amHehe, 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.

author: SiliconWizard
author_rank: Super Contributor
timestamp: August 05, 2019, 07:49:20 pm
content: Quote from: ArthurDent on August 05, 2019, 05:58:07 pmYes. I had it in my office a few years back. Ended up removing it because it was seen as offensive to some.

author: james_s
author_rank: Super Contributor
timestamp: August 05, 2019, 08:37:05 pm
content: Quote from: georges80 on January 30, 2015, 01:25:23 amI remember in a tech class in highschool (in the 90s) we had digital multimeters and I would sometimes sit there beeping the continuity beeper until someone would get upset. Beep beeeep beep beep beeeeeeeeeeeeeeep beeep beep... The teacher was in his late 50s and couldn't hear it, he'd give us funny looks before he figured out what was going on.