My Small Projects

The past few years, I have been working on my own Homebrew Amateur Radio projects, some are of my own design, and others are from; published schematic, from books, blogs or other sources. Most of my projects are small 9Volt QRSS Transmitters, Receivers, Beacons, or Audio Devices.

Lately my devices are becoming smarter as I include micro processors as part of the project. Most projects work very well, and yet, a few have been real flops. For example, when I crossed the input to the output lines on a PCB layout of an Audio Amplifier, it became an unintended-single-frequency-screaming oscillator.

Building Homebrew projects is one of the major aspect of Amateur Radio that I enjoy. In my much younger days, I built everything with the Idea doing QRO (high power) and getting the biggest 1000 watts on the air that I could afford. But, now my goal is to use as little electricity as possible.

My major contribution in my projects, is that; I enjoy making them as small as possible. When asked: "why try to make them so small?" Well, it is something like; "there are clock-makers, and there are watch-makers, I do it for the challenge".

After seeing some of my small projects, several people have asked; "would you sell one?". So far, I have not wanted to part with any of my Homebrew toys.

Well, maybe . . .

I have considering making a few of my Projects available, to anyone that would enjoy the novelty of them. To start, I could produce a few (to test the level of interest). The first few will probably be; completely Built and Tested. Later I may make Kits available if there is a demand. The Kits would only be for people that are looking for a microscopic building challenge and have the right tools.

Remember, the circuits that I plan to sell are "not anything new" and are things that "you can make yourself", using a PCB, "Manhattan", "dead bug" or "ugly style" of construction. But, you may find it a challenge to get it as small as my projects. That is what I plan to sell - the unique smallness.

The First Available Project

Initial Project

The first project that I have available, is the Micro-FM Transmitter (MFMT), as described in my previous posts, and which is a project inspired by Mark VandeWettering - K6HX of the braninwagon.com blog.

The original author of the circuit probably did not expect to see the circuit in this small form factor. The original circuit was Tetsuo Kogawa’s Micro FM transmitter.

I have additional ideas for this circuit, and soon they may show up here.

The MFMT PCB has been shrinking, in this latest revision, it only measures 0.5 x 0.5 inches. My initial blogged version was on a larger board (see the above photo). Moving the phone jack to the back side of the PCB allowed the board to shrink by about 1/3rd. Future revisions maybe even smaller :-) Most parts are now 0603 or 0805 SMDs. The double sided boards are designed with DipTrace and are being produced by DorkBotPDX.

Now For Sale - Revision Three
Ready to be mounted on a Battery
with Double Sided Tape

The MFMT uses a single SMT 2N3904. The output can be heard on a standard FM receiver on 107.5mHz (or near there). The jack and input accept stereo, but the resulting transmitted signal is mono. The usable range is about 30 feet. Which is more than enough to play my Cell Phone tunes on my car radio while driving. But yet, it is at such low power and the antenna length is so short, that I think it is well below any FCC requirements for licensing.

MFMT - Microscope View

This is my view through the microscope of the MFMT PCB, hand soldering at this scale is a little difficult. The 2N3904 is the center black rectangle and the resonate coil and variable capacitor is shown in the upper left. Audio come from the backside connector via the two summing resistors at the lower center. Battery connection is lower left, the Antenna is upper right. The Dime is for scale :-)

Resonate Coil and
a Needle Point for Scale

As can be seen, there is still open space for potential over all size reduction. But that will take many more hours of PCB layup time, and maybe even smaller parts.

See my "For Sale Page", at:
http://wa0uwh.blogspot.com/p/forsale.html

My goal was to make the MFMT available as cheap as possible, but without a facility for mass production it is still expensive. The first few are only for die-hard collectors that can help fund a start up.

I am not selling just the circuit's function, I am selling that function in a small size. Larger devices that will do the same function, will undoubtedly be much cheaper.

More to Build and Test

For now, I am only making Complete and Tested units available.

If you are interested, check the availability on the FOR SALE page, and reserve yours via e-mail, first come, first served.

If this all goes well with this initial offer, you may see more of my little projects listed.

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Update: Nov 21, 2013
Walt sent me the following link that described a VERY Small FM Transmitter:
http://engineering.columbia.edu/smallest-fm-radio-transmitter-0

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Micro FM Transmitter

Recently, Mark VandeWettering - K6HX of BrainWagon.org fame, posted his very interesting and success build of Tetsuo Kogawa’s Micro FM transmitter.

Following Mark's great inspiration, I decided to commit the circuit to a Micro PCB using small SMT components.

This project build was implemented using DipTrace PCB Software and the Homebrew Toner Transfer Method. Similar to my other Amateur Radio projects, my goal for this was to build the device as small as I my abilities allowed. The results, is a circuit board .5 x .8 inches, with about a third of that dedicated to the 1/8 inch audio connector. Some of the original circuit component values were change to accommodate the allotted PCB space and my junk box resources.

        

As Designed with DipTrace                   DipTrace 3D View

Printable Artwork

With a 9 Volt Battery and a twist of the Trimmer Cap, the circuit came alive on the FM Broadcast Band.

Initial testing indicates very good stability and it does not suffer from hand capacitance. It's DX has been tested to greater than 30 feet. I have not yet tested for expected battery life/usage, but so far one 9 Volt Battery has been running for greater that 4 hours (see UPDATE below), while listening to my phone tunes on the FM radio. I have not had to re-tune the receiver - it is very stable.

Mounted and Ready for Use

Click the images for expanded view.

The vertical component on the back edge is a 2.2p capacitor used as a short stub antenna, this simple small consistent load helps stabilize the frequency and provide a greater transmit range. The antenna length is just the original length of the component lead. Power (input or) output has not been measure (yet), but my similar constructed 30 meter beacons have typical measure 43nW into a 50 ohm load, but of course, this project is not terminated into a proper load and therefore the effective radiated power is unknown.

With a simple male-to-male stereo audio cable, the transmitter can be used with any PC or Phone style audio output.

The resulting circuit works very well, it is not stereo, but for now my Droid Phone has never sounded better on FM :-)

Thanks Mark for the build inspiration, and Tetsuo for the circuit design.

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UPDATE
At about 24 hours mark the output frequency shifted up about 2kHz.

For the Die Hard Test; A single 9 Volt Battery has now been powering this transmitter continuously for more than 96 hours.

At 96 hours I stopped the Die Hard Test to experiment with other aspects of this Transmitter. I think it is safe to say this Transmitter is very gentle on its battery.

AN OBSERVATION
An interesting observation: My HTC Droid Phone has an FM Receiver APP that can be used to listen to FM radio. Which I inadvertently turned it on, the audio was redirected to the audio output jack which was connected to the Micro FM Transmitter. In effect transcribing the Phone received FM station to yet another FM Broadcast Band frequency - as received on another FM receiver (my the FT-817). I think this may be border line illegal.

UPDATE
The MFMT is now even smaller, and available see: http://wa0uwh.blogspot.com/2011/12/my-small-projects.html



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