Minty FM Transmitter

March 7, 2011 by Kevin Dady 15 Comments

[Chis] wanted an FM transmitter bug device packed in a mint tin, and that is just what he made. Featuring only 17 discrete parts, running off of a 3volt coin cell battery, and small enough to fit inside of a plastic mint box and still have plenty of room for the mints.

Using a simple design the audio enters the device through a electret microphone and hits a transistor for amplification, the signal is then passed to the oscillator section of the circuit which features an LC tank type design which generates the carrier frequency and mixes that with the signal for a range of about 100 feet indoors.

Each section is broken down into steps where it is thoroughly explained with animations, theory, and simulation, if you are wondering how a transistor, wire, and capacitors make an FM transmitter, or if you would like to just make the final project, schematics, pcb files, and assembly instructions are provided as well.

Join us after the break for a short video and be sure to check out the other radio transmitters we have featured as well.

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Reverse Engineering Shopping Cart Security

February 28, 2011 by Mike Szczys 30 Comments

All this talk about 555 timers is causing projects to pop out of the woodwork like this one that reverse engineers a shopping cart security mechanism. The wheel seen above listens for a particular magnetic signal and when encountered it locks down the yellow cowl, preventing the wheel from touching the ground and making the cart very hard to move.

[Nolan Blender] acquired one of these wheels for testing purposes and he’s posted some details about the hardware inside. But the first thing he did was to put together some test equipment to help find out details about the signal that trips the mechanism. He connected a coil to an audio amplifier and walked around the market looking for strong signals. Once he found a few strong bursts with that equipment he grabbed an oscilloscope, hooked it to the coil, and made some measurements. He found an 8 kHz signal at a 50% duty cycle at 30 ms intervals (it would be hard to make a better case for why you need an oscilloscope).

With the specs in hand, [Nolan] grabbed two 555 timers, an audio amplifier, and a 200 turn antenna around a ferrite core to build his own locking mechanism. If you’re ever stopped short in the middle of the market, just look for the hacker at the end of the aisle holding the homemade electronics.

[Photo source]

[Thanks Colin]

AM/FM SOS Beacon Saves Your Bacon

February 27, 2011 by Mike Nathan 26 Comments

bacon_beacon_breadboard

[BadWolf] sent us a device called the “Bacon Beacon“, which is his 555 Design Contest entry. In short, it’s a life-saving device that emits an S.O.S. signal in Morse code over both the AM and FM bands. The device uses five 555 timers to get the job done, each of them dedicated to a specific task. Three of the timers are used for clocking and Morse generation, while the remaining two are used to produce and transmit an audible signal over the air waves. Currently, the signal can be received about a mile away from the source, which would theoretically allow for a search and rescue team to locate you with a simple radio and directional antenna.

The current design is still a bit rough around the edges, but the final plans would have the circuit built into a flashlight-like device equipped with red and green signaling LEDs. It’s a clever project and would make for a great tool if you got lost while hiking, or in the event of a zombie apocalypse.

Stick around for a quick video of the Bacon Beacon in action, and swing by [BadWolf’s] site if you want to know why his project has such a strange moniker (hint: it’s not because it can “save your bacon”).

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All-band Receiver Hides In Plain Sight

February 27, 2011 by Mike Szczys 17 Comments

This handheld radio has a little secret. You’re not going to be able to listen to Limbaugh since the original FM tuning circuit has been removed and replaced by a diode detector. Now [Miguel A. Vallejo] a discreet way to look for interesting radio signals in public.

The first step that he took was to remove the circuit board from the case and depopulate the tuning circuit while leaving the audio amplifier hardware. Next he referenced a proven design and built the diode detector circuit on a piece of protoboard. Finally he patched the new circuit into the original audio amplifier (seen in the image above) and put everything back in the case. Now he can listen in on data burst from a keypress on a computer keyboard, RF data communications, and slew of other noise sources.

This would be really handy for tracking down the electrical noise that’s screwing up your project.

[Thanks Superlopez]

Hear That? It’s A 555 Timer AM Radio

February 25, 2011 by Mike Nathan 16 Comments

[Eric] recently built an AM radio based on a 555 timer, and posted a few pictures to the Hack-a-Day Flickr pool. He used the 555 timer as an AM demodulator and power amplifier in order to drive the speaker. A hand-wound inductor is used to tune the signal which is then superimposed over the ramp signal produced by the circuit he built. [Eric] points out that he chose a CMOS 555 timer because of its superior performance in this particular application since the timer is used in a bit of a nontraditional manner. He shared his circuit diagram as well as a great video walking through each part of his design, finishing off with a demonstration of the radio, which can be seen below.

This is yet another great project that will be entered in the 555 Design Contest – simple and elegant. We love seeing these, so keep them coming!

If you want to see more cool projects made by Hack-a-Day readers, be sure to check out our Flickr pool as well as the forums.

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Launchpad Serial Morse Code Transmitter

February 11, 2011 by Mike Nathan 11 Comments

LaunchPad-Serial-Morse-Transmitter

LaunchPad dev boards from Texas Instruments are cheap and easy to program, making them a great Arduino alternative if you can do without some of the bells and whistles. [ech0s] put his to good use by constructing a Morse code transmitter with dual operating modes. The transmitter can not only encode and transmit messages entered in a terminal client, it also allows the user to send messages by manually operating the key switch. Inspired by the high altitude balloon transmitter we featured last summer, this project uses similar components for signal amplification and transmission. Text can be entered in a Putty terminal window, which then is encoded into Morse by the MCU before transmission. At the moment, the speed of the radio transmission is about 15 WPM, which is reasonably quick. Even though his system performs quite well [ech0s] has some improvements planned, including having a proper PCB built as well as some software tweaks to improve buffering and bandwidth. Be sure to check out his video of the transmitter in action after the jump.

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Building A Better Spectrum Analyzer For Radio Enthusiasts

February 8, 2011 by Mike Szczys 12 Comments

This spectrum analyzer project seeks to improve the quality of tools available to amateur radio operators. A lot of thought has gone into the design, and those details are shared in the verbose project log. The case was originally a CATV link transmitter, but most of the controls seen above have been added for this build, with unused holes filled and finished to achieve the clean look.

One noteworthy part of the build is the time that went into building a rather complicated-looking 1013.3 MHz cavity bandpass filter. Despite the effort, the filter didn’t work. Details are a bit sketchy but it seems that some additional tuning brought it within spec to complete that portion of the device.

This certainly makes other toy spectrum analyzers look like… toys.

[Thanks William]