Category: hardware

Last week I got my newest toy in. It's a USB DVB RTL Receiver featuring the Realtek chipset beloved by radio enthusiasts. The chip functions by receiving radio signals and converting them to audio streams which the computer can decode/demodulate using software. The software tells the chip what frequency to tune to, and demodulates the signal. This concept is known as a Software Defined Radio or SDR for short.

The Realtek is cheap and agile enough to tune a wide range of frequencies (52 MHz-2200 MHz). Thanks to free (as in beer) software like SDRSharp, the "work" of setting up this complex sounding setup is almost trivial. (Especially if you use the install script in the downloads section of SDRSharp. Other websites can show you how to setup a trunking radio scanner for police/fire/EMS in your area. [So long as your local fire responders don't use a trunked P25 Phase II system])

If you're looking to get started, check out this USB DVB Dongle (any RTL2832U receiver should work). I would also recommend getting an antenna pigtail so you can use a bigger/better antenna for whatever frequencies you want to receive.

I recently came across a schematic that showed how to build an oscillator using the NAND gates inside a 7400 chip. After poking around online, looking for the 7400 (and not some variant) I learned the LeTourneau University College of Engineering has a parts supply closet with a whole stash of them for 5¢ each. (I've known about the parts closet for quite a number of years, but only recently discovered a tall filing cabinet full of most commonly used ICs. (No NE602 or 612s, I'm afraid, but that's another post for another time.)

So, with my 7400 in hand, I was able to breadboard an oscillator using the "colorburst" crystal at 3.579 MHz. The oscillator emits a square wave at the fundamental frequency, so harmonics abound. In fact, just through playing around with another receiver, the 3rd harmonic at ~28.632 MHz is considerably stronger than the others that fall in the ham bands. (All higher harmonics are just above the ham bands, though I may be able to pull them back down with a variable capacitor in series with the crystal.) I need to do some range testing on this to see just how far I can get on the various bands.
My next trick is to build a bandpass filter network to dampen the harmonics down to legal levels. Then, I'll have a bona fide transmitter, though very, very low power. Perhaps a final amplifier is on the drawing board next.

I've decided to take the plunge and start working on a project that has been sitting in the back of my head since college. I'm setting out to build a CPU from scratch.

I thought that the Neodux crew might want to follow along as I work on this insane project. But not too insane...I've already figured out how I'm going to do it. I just need to do it now.

Follow along and watch as I walk the thin line between avocation and insanity!

...And I know some of you guys are EEs -- maybe you can give me a hand when something eventually goes wrong...

Well, today I received my first box from The Great Internet Migratory Box Of Electronics Junk. As predicted, there was a lot of random stuff inside. Several bags of discrete components (capacitors, LEDs, etc), some DC motors of varying sizes and ratings, some copper-clad PCBs for homemade etching (with transfer film - very tempting), a couple of pagers, some random gears and knobs, a nice pack of 7 segment LEDs, some project enclosures, some random PCBs, wire wrap supplies, a DIY 9-pin serial cable and connector, and a nice looking character LCD that was unfortunately cracked right in the center.

Quite a bit of stuff to choose from. I chose to take out a 9V battery clip, some 7-segment LEDs, and the 2 project enclosures. I plan to use the parts for a solar-powered arduino project I read about and have been wanting to try out.

I'll probably pick some unsuspecting geek and mail the box out to him in a couple days. That is, after I dig up some worthy additions to the box. Interested in joining the ranks? Sign up!

What a fun idea! The Great Internet Migratory Box Of Electronic Junk, TGIMBOEJ for "short", looks a like a neat prizefest for geeks all over. I know I'm all for it, I may even start a box of my own simply because I have so many extra electronic parts laying around! As the name implies it doesn't have to be just computer parts or just consumer electronics, it can be any electronic parts you happen to have. I have some leftover discrete components as well as PC parts I'm going to include should I receive a box soon. I've signed up on the wiki to put me in the pool of recipients. I'll, of course, let you know when/if I receive a box and what all I find useful in it. Sign up and send your old electronic parts to some random geek!