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7400 Oscillator
hardware : by Tommy - January 21st 2013, 10:51PM
hardware
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.

tags: electronics diy radio

( Comments : 1 | Full article )

 
Parallax Propeller
programming : by Tommy - July 21st 2012, 11:20AM
programming
I recently picked up a Propeller Board of Education from my recent trip to Parallax, Inc to teach the Teachers' Institute for the ARRL. The Propeller is Parallax's latest microcontroller platform that offers far more than the old beloved BASIC Stamp could. Digging back through my old posts, I found my initial review of the Parllax BASIC Stamp from 2006. (Little did I know that about 5 years later I'd begin teaching classes on the Stamp, visit Parallax HQ, and befriend the author of the "What's a Microcontroller" book (among other titles).)

The Propeller is a programmable multicore microcontroller that can be programmed in Assembly, Spin (an Object-Based programming language that I'm still learning), or, most recently, Standard C. The multicore design lends itself well for many, many projects, chief among them is robotics. Now your creations can take in and process loads more data at once. And with robotics, the more sensory input your bot has, the better equipped it will be to handle various tasks.

I just recently began to fully grasp the power of the little Propeller chip. Once the relative simplicity of utilizing the 8 cores available (known as "cogs"), the possibilities begin to multiply and compound one atop the other. My initial reluctance to the Propeller was the Spin language. The operators seem a bit foreign compared to the C-style languages I've been comfortable with for so long. The various code sections also seemed confusing initially. After reading through the tutorials posted on the learn.parallax.com website, I was up and running in a relatively short amount of time. I also took advantage of the Propeller Manual (pdf) and Programming the Propeller with Spin (pdf). While both offer great starting points, be sure to reference the learn.parallax.com site first - the Programming the Propeller text has its weaknesses.

Continue reading...

tags: microcontroller parallax propeller boe

( Comments : 0 | Full article )

 
Map Overlays
programming : by Greg - April 26th 2012, 03:58PM
programming
Since long long ago the military has used maps and graphic symbols to plan and implement combat plans. So to plan a mission, you need a MGRS topographic map, a blow up of the same map covering your Objective, and enough laminate overlays to fill a small car. I love arts and crafts just like the next guy, but is the sales guy at the mall gets a touchscreen tablet, why cant we get planning software. My list of needs: -a topographic version of Google Earth with Military Grid ref System -variable zoom and contour intervals -ability to capture snapshot the desired map -several tabbed 'layers' that I can toggle on and stack as needed -simple drawing tools -a tactical symbol database, one that recognizes the symbol I'm trying to fat finger and inserts it for me. That is all.

tags: military, maps, planning

( Comments : 0 | Full article )

 
HOWTO: Intro to Twitter
neodux : by Tommy - February 16th 2012, 11:40AM
neodux
For anyone online you've no doubt heard that social media is defined by sites like Reddit, Facebook and Twitter. A lot of people talk about Twitter, but a vast majority of people don't know how to use Twitter. I must admit that I've had an account for years but wrote it off because it seemed so limited. The power of Twitter is not found in the brevity of the "tweets" (posts that users make on Twitter), but in the ability to monitor tweets of others.

Flow of news
In the traditional model of news aggregation, you would turn on the TV or radio, open a newspaper or seek a sole source of information. That organization would have already done the leg work of finding news, picking out what they thought the majority of their viewers/listeners/readers would find appealing and put that news out there. With the introduction of "social media", suddenly people can discern for themselves what is important. The early days of Digg brought this idea to reality and reddit took over where Digg left off. The users were now in control of the information, not the producer, publisher or editor. I'm not saying that Twitter affords this ability, but it allows you to search for items that have been flagged with certain key terms. In Twitter parlance, this flag is known as a hashtag. Until I understood hashtags, I didn't "get" Twitter - now I do.

#Hashtags - The key to Twitter
Hashtags allow you to share information that you tweet with others within a community of individuals that are, themselves, looking for information relevant to a subject. The same way that you search for things with a search engine through key words, you can also hunt for tweets with a hashtag.
I deal a lot with Education Technology, so when I'm looking for news, links and information related to Education Technology, I'll look at the Twitter hashtag #edtech.

Continue reading...

tags: twitter howto

( Comments : 0 | Full article )

 
HOWTO: Getting Started with CW
radio : by Tommy - October 18th 2011, 05:50PM
radio
It's been a year since my post about Morse Code: Brief History, and I figure I might as well shed some light on how to get started operating with Morse Code. Since the Morse code requirement for ham radio was lifted in 2007, the number of amateurs getting their HF privileges has grown substantially, but with the "repeal" of code, entry level Technicians are granted privileges in certain portions of the bands. Most commonly, Technicians can operate SSB in the 10m band, but can also operate CW, or Morse Code, in 80m, 40m, 15m, and 10m. So, if you're a ham, you already have privileges to operate CW - you just need to learn where to start.

Learning the Code
For starters, you will need to learn Morse Code, one way or another. (duh.) While it may not be the universally agreed upon best way, I learned Morse Code through the Code Quick program. It really is an easy way to learn and quickly remember the code. There are countless gimmicks and "5 Minute Ab"-type programs that try to rush you through the learning process as fast as humanly possible, but few are ever successful. You just can't hurry the learning process. The downside of the CodeQuick method is not immediately known until you're trying to copy signals that are faster and faster. Once you hit about 10wpm, the CodeQuick lessons that you've used as a crutch finally become a hindrance and make copying code faster more difficult. The big plus is how quickly you'll learn the code in relatively enjoyable lessons compared to other methods.
Another alternative to learning the code is one of dozens of Koch method trainers. The Koch method, and most others, ram the code into your head seemingly through brute force.

Continue reading...

tags: ham radio cw morse code howto

( Comments : 0 | Full article )

 
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