Friday, December 23, 2011

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 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:

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.

Update: Nov 21, 2013
Walt sent me the following link that described a VERY Small FM Transmitter:


1 comment:

  1. I have need of an AM receiver about the size of a quarter or so and I am hoping for a 1.5 or maybe 3 volt supply requirement. Any ideas?