Electronics > Projects, Designs, and Technical Stuff
Bob Widlar's hassler circuit
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danadak:
Bob Pease article on hassler. Attached.


Regards, Dana.
texaspyro:
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. 
IDEngineer:

--- Quote from: georges80 on January 30, 2015, 01:25:23 am ---I built an oscillator circuit and a mate & I installed it into a homemade pencil case.
--- End quote ---
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.
_J_Herrmann_:
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

vk6zgo:
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.)
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