Monthly Archives: January 2007

How to (MARGINALLY) improve the range of a very cheap RF mouse


While shopping at Microcenter, I found a “bargain” wireless mouse and keyboard combination on sale for $12.99. I wanted to add something like this to my media center and the price was really low so I decided to give it a try. The first attempt at using this proved that you really do get what you pay for. Both the mouse and keyboard work fine if they are only a foot or two from the receiver, however, the mouse stops working intermittently as the range is increased. I opened the receiver up and noticed that it was an inductively coupled system running at around 27MHz. The receiver has a pair of MC3361 (one to receive keyboard and one to receive mouse),  low power FM IC and a single loop antenna. The mouse has a MA6221-S7K IC for a transmitter. The documentation for these chips has been very scarce, but what is available is at the bottom. The keyboard worked fine at large distances so I assumed it had a good antenna and didn’t bother taking it apart. It looks like the whole system is based on a reference design from Mosart, a Chinese company. Without having direct access to a network analyzer or standing wave ratio meter or lock-in amplifier, the two improvements that I could think of making were to “upgrade” the antenna and to change the squelch setting on the receiver ICs.

After playing with a few different designs, I settled on a 15-turn bundle of insulated wire to be attached in series with the single turn antenna on the board. Since I did not change the capacitors in the LC circuit, assuming the inductance was increased 16-fold, the resonant frequency of the circuit decreased to 1/4th. Again, without proper instrumentation, it is very hard to determine accurately what the actual resonant frequency is. My hypothesis was that even though the resonant frequency was lowered, the operating frequency was still a harmonic of the resonant frequency whose gain would be higher than what the original antenna circuit was. A better design here would be to replace the fixed capacitors with a variable 5-100pF cap and try to tune the antenna for better performance, but I didn’t have one laying around. The only thing that I could test was the effective range improvement which almost doubled making this device usable a few yards from the TV. This is acceptable for now, however, the next step is to try to determine if the squelch setting is hardwired for the device or if it can be made more sensitive by changing some biasing. Again, there are a-lot of ifs here, so your millage may vary.


mc3361.pdf ) ( ma6221-s7k.pdf )

Month of Apple Bugs has started…


Following the Month of Kernel Bugs and Month of Browser Bugs, the Month of Apple Bugs started yesterday. This interesting contest comes at a time when Apple is still supporting both the PowerPC and x86 versions of OS X, so there is a slight chance that some code has been overlooked. Beyond that, the bugs are not limited to the OS, third party software is also fair play. Finally, these bugs are presented in the style of full-disclosure where the security lists will get the notifications first. Let’s remember that nobody is perfect, and lets remember to have some fun.

(image is from vintage computer festival)

Roland EGX-300 links for 3D and PCB prototypes


Some time ago we good an EGX-300 engraver from Roland in the hope of doing small 3D and PCB prototyping. As far as the 3D goes, try the Modella tool that comes from Roland is not too useful for any kind of complex 3D design and most people seem to use VisualMill to generate the tool paths from standard 3D files. An example guide is over at instructables. The EngraveLab software that lots of EGX-300 vendors try to push with this device has so far proven to be fairly useless for 3D work and can be considered to be a waste of 1000USD for this application. (It turns out that EngraveLab is useful once you get some details worked out.)
As far PCB milling goes, pharmacy I have had a hard time finding a commercial package that will take a Gerber file and create a toolpath to send to an engraver without using some messy intermediate step. One guide is available from UMass which relies on PCBMill web utilities by C. Scott Ananian. These are written in JAVA but have some portability issues with the compiler available for OSX (workgroup server). I have email the authors of the UMass webpage and Ananian about commercial packages and have found none so far. I will try to compile PCBMill on a FreeBSD system next and will post the results. If anyone has reasonably priced alternative software suggestions, please let me know!

( pcbmill-098tar.gz )