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 put the transmitter from the previous post to the test. I changed the circuitry a bit though. I kept the oscillator (50 MHz) is now continuously powered. I programmed the ATTiny 2313 microcontroller (using PWM output) to send an oscillating signal to the base of a transistor (NPN). In this way the microcontroller PWM output didn’t supply power to the oscillator, but rather grounded it. I got a big boost in range this way. Yesterday I couldn’t even hear the signal in the parking lot of my apartment, whereas today I heard it loud and clear. I decided to take a drive with my scanner, laptop, and Argo to see how far away I could get and still detect the signal. With this bare bones transmitter setup (using a 2M J-pole antenna) I was able to detect it over 4,000 ft away. The receiving antenna was a 2m ~1ft high antenna magnet-mounted on top of my car.

This is the signal captured by Argo running on my laptop in my car as I drove away

In retrospect, I should have run Argo at my apartment and drove the transmitter farther and farther away. I presume that my transmitter is functioning decently, and that if I attached it to a proper antenna (and had a better receiving antenna) I might be able to get some cross-town distance? I’m still learning – this is the point though, right?

This is where I was when the signal died. The red marker (upper right) is my apartment where the transmitter was, and the signal began to die right as I traveled south on Chickasaw past Lake Underhill (~4000 ft away). This immediate loss may be due to the fact that I passed under power lines which parallel Lake Underhill which interrupted the line-of-sight path between my 3rd story apartment balcony and me. If this were the case, supposedly if I kept driving south the signal may have improved.





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.





One of my recent fascinations is QRSS, a super-low power mode of transmission over the airwaves. Picture this: get a ham radio setup which outputs dozens of watts of power, use a microcontroller to transmit data (frequency-shifting Morse code), use FFT on the receive end to view it on the computer, now increase the time between the “beeps” to tens of seconds and decrease the power to milliwatts and receive the signal thousands of miles away – that’s QRSS! How cool! I want to try this badly… but I have to get back to lab – I have a thesis to write!

This is one of my favorite images from my thesis. It’s a confocal z-stack projection using dual-color immunohistochemistry (red is autofluorescence)




After a few weeks of using InkScape, slowly working through documentation, tutorials, and practicing drawing random objects, I think I’m finally getting the feel of designing images in InkScape, and am growing to appreciate the depth of its usefulness. I’d love to have some great diagrams to include in potential publications. For example, I want a diagram to show how the autonomic nervous system innervates the mouse heart, but no such diagram exists! Here’s one for humans but it’s major overkill, shows every organ (I only want the heart), and doesn’t go into detail as to what the nerves do when they reach the heart (something I’m researching). Also, mouse brains are very different in shape from human brains, and there aren’t any good pictures of the ventral side of a mouse brain. So, I found the best one I could and re-created it with InkScape.

I used an existing image as a reference, made half a brain, and can mirror it when I’m done. It looks pretty good, right?





I’m posting this information hoping that someone else in a position similar to mine can benefit from the experience I gained through trial and error while trying to rapidly design and develop professional-looking QSL cards at low risk. I Googled around for this information, but didn’t find anything too helpful, so I figured I’d come up with something on my own and share my story.

QSL cards are like postcards which amateur radio operators often mail to one another after making long distance contacts. In addition to providing tangible proof of the communication, they’re cool mementos to tote around to remember who you’ve made contact with over the years. QSL cards display information bout the contact (time, date, call sign, frequency, signal report, etc.) and sometimes contain extra pictures/graphics which make them unique and appealing.

Once I got a HF rig for my apartment (a Century 21 CW-only HF rig which puts out ~30 watts), I started making contacts and getting QSL cards myself, so I wanted to send some nice ones in return. Being a poor college student (and a graduate student at that), I was extremely cash-limited, and didn’t want to sit around for weeks while my cards were professionally printed. This post describes how I created nice looking QSL cards in a few hours, for less than $0.25 each!

Step 1: Design the cards with the correct dimensions. The most cost-effective way to print nice digital images is my local Target (a store with a 1-hr photo lab which accepts JPEGs as the image source for $0.20 cents a picture), but the snag was that they only print 4” x 6”. QSL cards need to be 3.5” by 5.25”. I used Inkscape to create an image exactly 4” by 6”, and inside of it I drew a border 3.5” by 5.25”. Everything outside that border I made black. I designed my QSL card inside that border, such that when the images would be printed I could trim-off the black border and have a perfect 3.5” by 5.25” QSL card.

Step 2: Print the reverse side on full-size label paper. All I needed was some framed boxes for QSL information, so I quickly sketched up the design in Inkscape and saved it in the same format as before (4” by 6”). I left a LOT of white space around the edges so it’s very forgiving down the line. I then printed the design on full-page label paper (full-sheet stickers, available at most office stores cheaply in the printer paper section), placing 4 “backs” per page.

03_backs

Here’s what the adhesive paper looked like after printing:

04_cutback
05_back

Step 3: Attach backings to QSL cards. This part is easy if you have a paper cutter. I purchased mine ~5yrs ago and I *LOVE* it. It’s almost as useful as my soldering iron. Seriously, so convenient. I wouldn’t dream of doing this with scissors! Anyhow, roughly cut the sticker paper into quarters.

06_peel
07_overhang

Next, peel and stick on the backs of cards. Don’t worry about overhang, we’ll take care of that later…

09_cut
10_nice

Step 4: Trim the edges. Make sure you do this step after applying the sticker. This was the secret that I wish I realized a while ago. If you trim first, sticker placement is critical and difficult. If you place the sticker before you trim, you get perfect edges every time.

11_niceback

How nice does that look? If you did your math correctly, your new dimensions should be exactly 3.5” by 5.25”.

12_silver2

Step 5: fill-out information. I decided to use a metallic Sharpie to write the name of the call sign I send this to on the front of my card. How cool does that look? This is what the front/back of this card looks like after filling it out.

12_donefront

I hope this information helps you. If you print your own QSL cards using this (or a similar) method, let me know about it! I have to say, for ~5 / $1, these don’t look to bad. It’s especially useful if you only want to print a few cards! Good luck.
— Scott, AJ4VD





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 working on a homemade ECG machine over the last month. This is the most basic circuit I’m currently using, designed using two quad op-amps. I’ve produced some surprisingly good ECG traces and even identified an arrhythmic heartbeat. Currently the device is limited because you have to be attached to your computer, I’m working toward making it a mobile device (powered by a 9V battery) which records voltage data to a minidisc recorder . There’s one problem – I need to optimally adjust the gain, but how if I cannot see the trace of the wave on a monitor? I could a VU meter to monitor the output… My minidisc recorder can take mic-in and echo it the line-out at the same time, so I’ll just put the VU meter on the line-out and it shouldn’t affect my trace. The result is that I can walk around for 24 hours, recording my ECG, with a device I hope to get down to the size of a cell phone. (Maybe a 1990s cell phone?)

Here’s a simple LED-based digital VU meter circuit I found, along with some sample images of its (bread-boarded) construction. I have all the parts at home I think, so it should be straightforward to make. The pain now is the electrodes (which are still the junky ones made from scissor-cut aluminum cans), and I think I might splurge and buy some actual disposable ECG electrodes. I think the total cost of my device as it stands is about $4, so I don’t want to spend more than I have to on electrodes.

In other news it appears I’ve been accepted into dental school. I got a voicemail this morning at 8am, another one at 12:30pm, and apparently one on my parents’ answering machine (I listed them as an alternate number), then they sent me an email! Naturally it was the email I noticed first. Here’s a snapshot from my inbox, phone call 1 and phone call 2.