Annoy Your Enemies with the Hassler Circuit

[Craig] recently built himself a version of the “hassler” circuit as a sort of homage to Bob Widlar. If you haven’t heard of Bob Widlar, he was a key person involved in making analog IC’s a reality. We’ve actually covered the topic in-depth in the past. The hassler circuit is a simple but ingenious office prank. The idea is that the circuit emits a very high frequency tone, but only when the noise level in the room reaches a certain threshold. If your coworkers become too noisy, they will suddenly notice a ringing in their ears. When they stop talking to identify the source, the noise goes away. The desired result is to get your coworkers to shut the hell up.

[Craig] couldn’t find any published schematics for the original circuit, but he managed to build his own version with discrete components and IC’s. Sound first enters the circuit via a small electret microphone. The signal is then amplified, half-wave rectified, and run through a low pass filter. The gain from the microphone is configurable via a trim pot. A capacitor converts the output into a flat DC voltage.

The signal then gets passed to a relaxation oscillator circuit. This circuit creates a signal whose output duty cycle is dependent on the input voltage. The higher the input voltage, the longer the duty cycle, and the lower the frequency. The resulting signal is sent to a small speaker for output. The speaker is also controlled by a Schmitt trigger. This prevents the speaker from being powered until the voltage reaches a certain threshold, thus saving energy. The whole circuit is soldered together dead bug style and mounted to a copper clad board.

When the room is quiet, the input voltage is low. The output frequency is high enough that it is out of the range of human hearing. As the room slowly gets louder, the voltage increases and the output frequency lowers. Eventually it reaches the outer limits of human hearing and people in the room take notice. The video below walks step by step through the circuit. Continue reading “Annoy Your Enemies with the Hassler Circuit”

Ask Hackaday: Can you Hack an Appliance into a Spy Device?


A story surfaced a few days before Halloween on Russian news site Rosbalt (yep, that’s in Russian), claiming Russian authorities intercepted Chinese-made electric irons and kettles: each equipped with microphones and WiFi. You can read a summary in English on the BBC’s website. The “threat” imposed by these “spy appliances” is likely the result of gross exaggeration if not downright fear mongering against Chinese-made products. It’s not worth our (or your) effort to speculate on what’s really happening here, but the situation does present a fun exercise.

Say you wanted to spice up your pen testing by altering a small home appliance: how easily could you build it? Let us know in the comments which appliance would serve as the best “host” for the modifications and what features you would include. Could you manage all the components listed in the article–a microphone, WiFi (any chance of cracking unsecured networks?), plus some vague indication that it “spreads viruses?” There’s a video below with a few glimpses of the electronics in question, but unless you speak Russian it probably won’t offer much insight.

Continue reading “Ask Hackaday: Can you Hack an Appliance into a Spy Device?”

A cortex M4 based platform with ETH, USB, BT and many on-board peripherals

Here is a very time consuming project that I worked on during last summer: an ARM Cortex M4 based platform with plenty of communication interfaces and on-board peripherals. The particular project for which this board has been developed is not really HaD material (one of my father’s funny ideas) so I’ll only describe the platform itself. The microcontroller used in the project is the ATSAM4E16C from Atmel, which has 1Mbyte of flash and 128Kbytes of SRAM. It integrates an Ethernet MAC, a USB 2.0 Full-speed controller, a sophisticated Analog to Digital Converter and a Digital to Analog Converter (among others).

Here is a list of the different components present on the board so you can get a better idea of what the platform can do: a microphone with its amplifier, a capacitive touch sensor, two unipolar stepper motors controllers, two mosfets, a microSD card connector, a Bluetooth to serial bridge, a linear motor controller and finally a battery retainer for backup power. You can have a look at a simple demonstration video I made, embedded after the break. The firmware was made in C and uses the Atmel Software Framework. The project is obviously open hardware (Kicad) and open software.

Continue reading “A cortex M4 based platform with ETH, USB, BT and many on-board peripherals”

Echolocation pinpoints where a gunshot came from


[Kripthor] suspected that hunters were getting too near his house. When thinking of a way to quantify this belief he set out to build a triangulation system based on the sound of gunshots. The theory behind it is acoustic location, which is a specialized type echolocation.

The most common example of echolocation is in Bats, who emit ultrasonic noise and listen for its return (echo) to judge the location of objects. [Kripthor] doesn’t need to generate the sound himself, he just needs to pick it up at different points. The time difference from the three samples can be used to triangulate coordinates as seen in the image above.

He first tried using a PC sound card to collect the samples. The stereo input only provides two channels so he tinkered around with a 555-based multiplexing circuit to sample from three. The circuit noise created was just too great so he transitioned to using an Arduino. The ADC samples from each microphone via an NPN transistor which is used as a simple amplifier.

This brings to mind a homebrew sonar hack from way back.

Voice controlled video game uses “Biu” and “ahh” for control


This video game gives your thumbs a rest while stretching those vocal chords. The pair of microphones seen above control the video game on the LCD display. Saying “Biu” will launch a projectile while “ahh” adjusts the flight path. The system was developed by [Tian Gao] as a final project for his ECE 4760 course at Cornell University.

The inputs are common computer microphones connected to some processing circuitry which he built on a piece of protoboard. This consists of some RC filtering and an LM358 opamp to get the signal ready for use with the ATmega1284. There is only one ADC on that chip so [Tian] alternates sampling from the microphones by using the multiplexer built into the chip. The video signal itself is an NTSC composite signal. To facilitate a reasonable frame rate he uses graphics that are packed in multiples of 8-bits. All in all this allows him to create a 160×200 pixel display.

All of this makes the game sound a little dry, but we dare you to listen to the video clip after the break without cracking a smile.

Continue reading “Voice controlled video game uses “Biu” and “ahh” for control”

How to add audio in to the Sony NEX-5 line of DSLR cameras

[Tynan] loves his Sony NEX-5 camera but he’s fed up with not being able to choose any external microphone when recording video. Recently he set out to remedy that, and managed to add an audio in jack without modify the camera itself.

The real trick here is to modify how a microphone accessory connects to the camera. In [Tynan’s] tutorial video (embedded after the break) he uses the enclosure from a flash module as a connector. After removing the electronics he’s left with plenty of room for the guts of a Sony microphone accessory. Those include the PCB and wiring, but not the microphone element itself. A 3.5mm audio jack is added to the flash case, and soldered to the microphone cable. Now he has a modular audio-in jack. The only problem is that his tinkering resulted in mono only. If you don’t mind spending a bit more time reverse engineering the scrapped microphone we bet you can parlay that into a true stereo option.

Continue reading “How to add audio in to the Sony NEX-5 line of DSLR cameras”

Roll your own parabolic microphone

Parabolic microphones are used to listen in from a distance. You see them on the sidelines of NFL football games, but they’re part of the standard issue in detective and spy novels. Now you can build your own parabolic microphone by following this example.

The one component that may be hard to find is the parabolic reflector. You cannot simply use a bowl or other curved object as the precise parabolic shape ensures that sound waves are reflected onto one finite focal point. For this build the reflector was obtained from an eBay seller. But the other parts are scavenged from easy to find sources. The microphone itself is an inexpensive element from Radioshack. It is mounted in the shell from a tweeter speaker, which helps to gather the sound if the element isn’t exactly aligned with the focal point. The setup also needs a preamplification system, which uses many components. Luckily there’s a schematic and other reference material linked in the write up.

You can also build a laser microphone which detects sound waves on a pane of glass.

[Thanks Anonymous]