Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

I’ve been very busy over the past couple weeks. Last Thursday my boss approached me and asked if I could work over the weekend. He wanted to complete and submit a grant by the deadline (Monday at 5 pm). To make a long story short I worked really hard (really long days) on Friday, Saturday, Sunday, and Monday to accomplish this. Monday afternoon when it was done (at about 4 pm), after which I went home and collapsed from exhaustion. I don’t know how my boss does it! He worked on it far more than I did, and over that weekend he didn’t sleep much. Anyway, in exchange for my over-weekend work I got Tuesday and Wednesday off.

I knew in advance that I’d have two days off to do whatever I wanted. I prepared ahead of time by ordering a small handful (I think 4?) of ATMEL AVR type ATTiny2313 chips from Digi-Key at $2.26 per chip. They arrived in the mail on Monday. Unlike the simple PICAXE chips which can be programmed a form of BASIC cod from 2 wires of a serial port, the AVR series of chips are usually programmed from assembly-level code. Thankfully, C code can be converted to assembly (thanks to AVR-GCC) and loaded onto these chips. The result is a much faster and more powerful coding platform than the PICAXE chips can delivery. PICAXE seems useful for rapid development (especially if you already know BASIC) but I feel that I’m ready to tackle something new.

I built a straight-through parallel programmer for my ATTiny2313 chips. It was based upon the dapa configuration and connects to the appropriate pins. To be safe I recommend that you protect your parallel port and microcontrollers by installing the proper resisters (~1k?) between the devices, but I didn’t do this.

I decided to dive right in to the world of digital RF transmission and should probably go to jail for it. I blatantly violated FCC regulations and simply wired my microcontroller to change the power level given to a 3.579545 MHz oscillator. The antenna is the copper wire sticking vertically out of the breadboard.

These crystals release wide bands of RF not only near the primary frequency (F), but also on the harmonic frequencies (F*n where n=1,2,3…). I was able to pick up the signal on my scanner at its 9th harmonic (32.215905 MHz). I think the harmonic output power is inversely proportional to n. Therefore the frequency I’m listening to represents only a fraction of the RF power the crystal is putting out at its primary frequency. Unfortunately the only listening device I have (currently) is the old scanner, which can only listen above 30 MHz.

Remember when I talked about the illegal part? Yeah, I detected harmonic signals being emitted way up into the high 100s of MHz. I don’t think it’s a big deal because it’s low power and I doubt the signal is getting very far, but I’m always concerned about irritating people (Are people trying to use Morse code at one of the frequencies? Am I jamming my neighbors’ TV reception?) so I don’t keep it on long. Once I get some more time, I’ll build the appropriate receiver circuits (I have another matched crystal) and install a low-pass filter (to eliminate harmonics) and maybe even get a more appropriate radio license (I’m still only technician). But for now, this is a proof-of-concept, and it works. Check out the output of the scanner.

Something I struggled with for half an hour was how to produce a tone with a microcontroller and the oscillator. Simply supplying power to the oscillator produces a strong RF signal, but there is no sound to it. It’s just full quieting when it’s on, and static noise when it’s off. To produce an AM tone, I needed amplitude modulation. I activated the oscillator by supplying power from the microcontroller with one pin (to get it oscillating), and fed it extra juice in the form of timer output from another pin. The fluctuation in power to the oscillator (without power-loss) produced a very strong, loud, clear signal (horizontal lines). I wrote code to make it beep. Frequency can be adjusted by modifying the timer output properties. The code in the screenshot is very primitive, and not current (doesn’t use timers to control AM frequency), but it worked. I’m sure I’ll write more about it later.

Thoughts from Future Scott (August 2019, 10 years later):

What a good start! But what a bad design =P

Driving a can oscillator’s power pin with two microcontroller pins is not a good idea. Also, you were SO CLOSE to getting frequency shift keying to work! Rather than turning the can oscillator on/off with the microcontroller, just leave it on continuously and send a microcontroller pin to the can oscillator’s VCO pin. I’m sure I didn’t know what that 4th pin does when did when I originally wrote this (and most diagrams of can oscillators online leave that pin disconnected).

Either way, I’m happy this day happened – this was the start of years of hobby radio frequency circuit design!





Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

Over the last couple weeks whenever I had the time I’d work on creating a little Morse code keyer. After a few different designs I came up with the winner. Basically it just uses a bar of aluminum which rocks on a metal pin. Thumb-screws on each side of the balance point (fulcrum?) can be adjusted to modulate the distance the paddle has to go down to be activated, and how high the paddle goes up when released. A couple springs (one pull-type and one push-type) help give it a good bounce between keys. Two knobs control volume and frequency. I especially like the ability to control the frequency! A capacitor inline with the speaker helps smooth the output a bit too. It’s not professional, but hey – for a couple bucks of parts I made a functional keyer and had fun doing it. Now I guess I should put more time into learning Morse code…

Thoughts from future Scott (August 2019, ten years later)

Wow this is rough! I’m 90% sure this is based on a 555 circuit. lol @ the use of Jenga blocks. It looks like the wire was sourced from cat5 cable. That aluminum slab later became the base and heat sink for an IRF510-based push-pull amplifier.





I’ve taken the plunge into the geek world by becoming a licensed amateur radio operator. My wife and I both took our technician exam last week, and this morning I discovered that our call signs have been processed. I’m KJ4LDF, she’s KJ4LDG. I’m a little disappointed that my call sign has an “F” in it. On the air, “F” and “S” sound similar, so I’m more likely to have people asking me to repeat it. The phonetics are Kilo, Juliet, Four, Lima, Delta, Foxtrot. Foxtrot! How silly is that? [sighs] Either way, I’m glad I’ve been added to the database, and am now legally able to begin broadcasting on VHF/UHF.

Beacon stuff (like I wrote about in the last post) would best involve lower frequencies, which would mean I have to take another exam to get a higher license class.





Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

I got an idea today for an odd but interesting project. The idea is still in the earliest stages of development, and I further research the idea (for example, I don’t even know if it’s legal) but it’s a cool idea and I want to try it. I know I’ll learn a lot from the project, and that’s what’s important, right? So, here’s the idea: I want to build an incredibly simple, low power radio transmitter that broadcasts data on a fixed frequency. Data is provided by a microcontroller. What data will it transmit? uh… err… um… okay it doesn’t really matter and I don’t even know, I just want to do this project! Maybe temperature and light intensity or something. Who cares – it’d be fun to make regardless of what it transmits. I could put it all into a drybox (pictured).

Once properly closed, this box will keep everything in pristine working condition by protecting against rain, heat, snow (not that we get much of that in Orlando), hurricanes, and perhaps even Florida panthers and bears (oh my). I’d like to make a glass (or plexiglas) window on the top so that light could get in, hitting solar panels, which trickle-charges the battery housed in the device as well.

My idea is to keep construction costs to a minimum because I’m throwing this away as soon as I make it. My goal is to make it work so I can toss it in some random location and see how long it will run. Days? Weeks? Months? Years? How cool would it be to go to dental school, come back ~5 years from now, and have that transmitter still transmitting data. I’ve been poking around and I found someone who did something similar. They built a 40mW 10m picaxe-powered beacon using a canned oscillator as the transmit element.

I understand the basics of radio, amplitude and frequency modulation (AM and FM), etc., but I’ve never actually built anything that transmits radio waves. I could build a SoftRock radio, but my educational grounding is in molecular biology. I know little about circuit-level electronics, electrical engineering, and radio theory… so my plan is to start small. This project is small enough to attack and understand, with a fun enough end result to motivate me throughout the process.





Warning: This post is several years old and the author has marked it as poor quality (compared to more recent posts). It has been left intact for historical reasons, but but its content (and code) may be inaccurate or poorly written.

Two hours after getting home from work I’m already basking in the newfound carefreeness thanks to the successful completion of my thesis defense (and graduation requirements). Yesterday I went to SkyCraft, early this morning I posted a schematic diagram of a basic circuit concept for a radio/microphone interface box with tone generating functions, and this afternoon I finished its assembly. It’s hacked together, I know, but it’s just a prototype. What does it do? It’s complicated. It’s basically just an exercise in microchip programming.

Future Scott reacts to this in August, 2019 (10 years later)

LOL! That’s a pipette box! A chip socket was sunk into a plastic enclosure somehow! And that “regulated power supply” is an LM7805 on non-metallic perfboard screwed to two Jenga blocks!

Here’s the little setup with the main control unit and a DC to DC regulated power supply / serial microchip programmer I made.

Here’s the main control box. Notice the “2-way lighted switches” which I described in the previous entry. I found that proper grounding (floating pin prevention) was critical to their proper function. I’m still new to these chips, so I’m learning, but I’m making progress!

Getting a little artsy with my photographs now… this is the core of the device. It’s a picaxe 14m!

This is a 5v regulated power supply I built. The headphone adapter is for easy connection to the serial port. It has a power switch and a program/run switch (allowing use of pin 13, serial out) while still “connected” to the PC.

I’ve slightly improved the connection between my radio’s coax cable to the J-pole antenna I made.

I’m able to get pretty good from this antenna, but it’s probably not likely to do much to my assembly skills (and lack of tuning), and more likely due to the fact that I have an unobstructed view of middle/southern Orlando from the 3rd story of my apartment balcony. I could probably wire up a rubber duck on a stick and get good results with that location! I’ll miss my reception when I move.