Tiny FM Transmitter Bugs Rooms

October 21, 2010 by Mike Szczys 30 Comments

Lucid Science delves into spy-tech once again with this tiny FM transmitter. Their post demonstrates a bit larger version than seen above, using a 9-volt battery and protoboard sized to match which makes for easier soldering. The design uses a microphone, two transistors, enameled wire for the coil, as well as various resistors, capacitors, and a potentiometer. What you end up with is an amazingly clear audio signal that can be picked up with a normal FM radio.

This would make a great project to do with the kids. You can talk about circuit design, practice soldering, and when finished they’ve got an almost miraculous toy to play with. Just be careful what you say around the house, the room might be bugged!

Data Confirmation With RF Communications

October 18, 2010 by Mike Szczys 35 Comments

[Rafael] built a system that uses radio frequency for communications. The code he was using with the inexpensive receiver/transmitter pairs already had some error correction but from time to time an entire message would be missed by the receiver. He set out to make these RF communications more robust.

A little more than a year ago we looked at using these same transmitters with an Arduino. [Rafael] has a similar setup but since they are unidirectional he chose to use two pairs for bidirectional communication (each operating at a different frequency to avoid interference). On one end, a computer transmits data to the Arduino which is in a remote location. His confirmation protocol relies on a randomly generated message identifier. The computer will continually transmit the same message. The Arduino continually receives these messages, comparing them with the last successfully received message. If they match, it is considered a successful data transfer and the Arduino transmits a confirmation back to the computer which then starts transmitting the next message.

This isn’t an application-specific protocol. For demonstration purposes [Rafael] built a quick home automation setup that uses it to operate a house lamp.

A Simple FM Transmitter

September 25, 2010 by Mike Szczys 34 Comments

Here is a low component count FM transmitter. It sacrifices some features, like the ability to adjust the frequency, for simplicity’s sake. The build method is fairly common with amateur radio but we don’t see it around here too much. Each component gets a 5mm-by-5mm copper clad pad which is super glued to the ground plate as an insulator. There’s even a pictorial example of this method if you need some help with visualization.

One of the schematics included in the article shows how to incorporate a condenser microphone into the unit. We guess that makes it pretty easy to add an FM ‘bug’ to your arsenal of covert listening devices. Just make sure to check your local laws before building and using this. We’re not sure what the FCC would think of it here in America so we’re hoping some well-informed readers will educate us with a comment.

[Thanks Bart]

1953 Radio Includes Tubes, AM, FM, And MP3

September 7, 2010 by Mike Szczys 16 Comments

This vintage radio can play AM, FM, and MP3, all with a classic sound. Inside you’ll find a new AM radio tube-amp, providing the functionality you’d expect from the device. The rest of it comes from a conglomeration of parts; an FM receiver board from another radio and an MP3 player with remote control and USB connector. The classic sound we mentioned above comes from an AM modulator. That’s right, the auxiliary audio boards aren’t connected directly, but are broadcast on the AM band so that your latest MC Lars album has the same sound quality as the traffic report.

Check out this similar project from last year that adds RDS to a vintage radio.

Giving An IR Transmitter Some Strength

August 22, 2010 by Mike Szczys 17 Comments

[Jkx] was using a Thomson VS360U video transmitter to make a wireless connection between a cable box and his television. The system using an RF remote, but relies on an IR transmitter to communicate between the base station and the cable box. He found the IR module that comes with the device is under-powered and set out to fix the situation. Using a scope he found the pin that drives the IR LED. The board above contains a boost circuit that patches into voltage and ground, using the pin he sniffed out to control the base of a transistor. Now the device has enough power to reliably control the cable box.

Adding Motion Control To An RC Transmitter

June 25, 2010 by Mike Szczys 5 Comments

If your soldering skills are up to snuff you can add a motion control feature to your radio controlled transmitter. [Starlino] used a combination accelerometer and gyroscope module as an alternate source of analog control information. He built a filter to dial in the analog voltage range to match that of one of the sticks on the controller. A switch is used to disconnect the signal when motion input is not desired. This would be a nice addition to one of those more creative aerial hacks.

All About VLF Radio

April 14, 2010 by Mike Szczys 20 Comments

If you’re interested in learning about Very Low Frequency communications take a look at what Larry has to offer on his site. He’s put together a guide to VLF receivers that is short enough to read and clear enough to understand with rudimentary knowledge of circuits. He builds a simple receiver as a working example and a high-powered transmitter that can put out over 2600 watts. Let’s face it, radio operators were the original electronic hackers. Get back to our roots and learn the ways of the transistor.

[Thanks Buddy]