In April 2012 I had some alarming symptoms and visited an oncologist for the first time. Symptoms included lymphadenopathy, weight loss, night sweats. This picture was taken just before my first doctor visit, and I’m in scrubs because I was a dental student at the time (I hadn’t started the DMD/PhD program yet). After several blood tests and two surgical biopsies I was eventually diagnosed with non-Hodgkin’s lymphoma (NHL). More specifically, Lennert’s Lymphoma, a rare lymphoepithelioid variant of peripheral T-cell lymphoma in the not otherwise specified category T-cell lymphomas.
I found one of K. Lennert’s early publications from 1986 especially interesting. There are earlier publications, but this one is open-access. Its title describes condition as “a monoclonal proliferation of helper T cells“, and in its text further characterizes it as “special variant of Hodgkin’s disease characterized by a high percentage of epithelioid cells and rarely containing the Reed-Sternberg cells characteristic of classical Hodgkin’s disease.”
Markdown source code last modified on January 18th, 2021
---
title: First Diagnosis
date: 2012-04-16 21:00:00
tags: med
---
# First Diagnosis
**In April 2012 I had some alarming symptoms and visited an oncologist for the first time.** Symptoms included lymphadenopathy, weight loss, night sweats. This picture was taken just before my first doctor visit, and I’m in scrubs because I was a dental student at the time (I hadn’t started the DMD/PhD program yet). After several blood tests and two surgical biopsies I was eventually diagnosed with [non-Hodgkin’s lymphoma (NHL)](https://g.co/kgs/yBJEYd). More specifically, Lennert’s Lymphoma, a rare lymphoepithelioid variant of peripheral T-cell lymphoma in the [not otherwise specified category](https://en.wikipedia.org/wiki/Peripheral_T-cell_lymphoma_not_otherwise_specified) T-cell lymphomas.
<div class="text-center img-border">
[](visit1.jpg)
</div>
**I found one of K. Lennert’s [early publications](http://www.bloodjournal.org/content/bloodjournal/68/3/663.full.pdf) from 1986 especially interesting.** There are earlier publications, but this one is open-access. Its title describes condition as “a monoclonal proliferation of helper T cells“, and in its text further characterizes it as “special variant of Hodgkin’s disease characterized by a high percentage of epithelioid cells and rarely containing the Reed-Sternberg cells characteristic of classical Hodgkin’s disease.”
As many of you know, my wife Angelina Harden unexpectedly passed away a couple days ago (Saturday, Aug 20, 2011). I'd like to thank all of our friends for their encouraging words. This is an extremely hard time for her family, my family, and me, and I appreciate the outpouring of support and encouragement.
Angelina's funeral was held in Jackson, Tennessee (the home town of much of Angelina's family and friends from her past) on September 10th, 2011. A memorial service was held in Gainesville, Florida (mostly attended by my family and college students from my dental school and Angelina's nursing school) on September 25, 2011. Both services were amazing, and I thank everybody who worked to make them so wonderful - it was a truly beautiful way to remember Angelina. Anelisse Martinez (a dental school classmate, and friend of Angelina and me) sang to an instrumental version of all 3 songs. For the last song, she was accompanied by Dennis Beliveau (another dental school classmate, and friend of Angelina and me). Dennis also sang Tears in Heaven, by Eric Clapton. These songs, in combination with the wonderful messages shared by Angelina's friends, made the service a joyful and moving experience. I'm fortunate to be surrounded by so many wonderful people. I ask for your continued thoughts for Angelina's family, her friends, and me - Angelina was loved so much, and her passing is hard for everyone who knew her. Thank you for your kindness.
Markdown source code last modified on January 18th, 2021
---
title: We Love and Will Miss You, Angelina
date: 2011-08-23 01:08:43
---
# We Love and Will Miss You, Angelina
__As many of you know, my wife Angelina Harden unexpectedly passed away a couple days ago__ (Saturday, Aug 20, 2011). I'd like to thank all of our friends for their encouraging words. This is an extremely hard time for her family, my family, and me, and I appreciate the outpouring of support and encouragement.
__Angelina's funeral__ was held in Jackson, Tennessee (the home town of much of Angelina's family and friends from her past) on September 10th, 2011. A memorial service was held in Gainesville, Florida (mostly attended by my family and college students from my dental school and Angelina's nursing school) on September 25, 2011. Both services were amazing, and I thank everybody who worked to make them so wonderful - it was a truly beautiful way to remember Angelina. Anelisse Martinez (a dental school classmate, and friend of Angelina and me) sang to an instrumental version of all 3 songs. For the last song, she was accompanied by Dennis Beliveau (another dental school classmate, and friend of Angelina and me). Dennis also sang Tears in Heaven, by Eric Clapton. These songs, in combination with the wonderful messages shared by Angelina's friends, made the service a joyful and moving experience. I'm fortunate to be surrounded by so many wonderful people. I ask for your continued thoughts for Angelina's family, her friends, and me - Angelina was loved so much, and her passing is hard for everyone who knew her. Thank you for your kindness.
<div class="text-center img-border">
</div>
Last year a group of high school students, in collaboration with a seminar course on Space Systems sponsored by the University of Florida's Student Science Training Program (SSTP), gained some real-world experience planning, building, and launching a research payload to the edge of space – all in a couple weeks! Last year's high altitude balloon launch was covered on my website, and the radio transmitter I built for it was featured on this Hack-A-Day post. Unlike last year's payload, whose only homebrew device was the radio transmitter, this year's payload had equipment we assembled ourselves, and instead of launching from NASA we launched from the UF football stadium! There were a couple problems along the way, and the payload hasn't been recovered (yet), but it was a fun project and we all learned a lot along the way!
Below is a panoramic photo right before the launch - see our balloon on the right? So cool!
Our goal was to take photos from the edge of space, and log temperature, pressure, humidity, and GPS coordinates along the way. On-board were a radio transmitter, an Arduino with a GPS shield, and an Android phone to take pictures every few seconds.
Android details: Most of the Android development was handled by UF student Richard along with high school students Benji, Tyler, Michael, and Kevin. Their GitHub project is here:https://github.com/rich90usa/AndroidSensorLogger. Also note that the automatic photo capture utilized Photo Log Lite. We also used GPSLogger to handle logging GPS to SD. "Both of these programs were chosen for their ability to run in the background - and do so reliably by using the 'correct' Android supported methods of doing so." -- Richard
Our code used the phone's text-to-speech engine to speak out an encoded version of every 90th new GPS coordinate. The data was encoded by connecting every number (0-9) to a word the NATO phonetic alphabet. The code also used text-to-speech to have the phone speak out the phone's altitude data. --Benji
The device consisted of 4 main components: a payload (the styrofoam box in which all of the electrical equipment was housed), a radar reflector (hanging off the bottom of the payload, to help make this object visible to aircraft), a parachute (at the top, made of bio-degradable plastic), and the balloon itself which measured about 6 feet wide when inflated at ground level (supposedly it reaches approximately 30 feet wide at high altitudes before it bursts). Once the balloon bursts, the parachute fills with air and the device floats back to earth.
Kunal demonstrates the effectiveness of our parachute with a scientific "run test"!
The radio communication system we used this year were a little more commercial than last year. Due to my limited time availability (I had an oral surgery rotation all week the week before launch), I chose to get something pre-packaged. My intent was to use FRS (those little 500mW family radio service radios) to send GPS data back to earth, but I later (after launch) did a little more research and realized that it probably wasn't the most legal way to do it. However, it was extremely cost effective (amateur radio transmitters and RF transmitter modules are quite pricey). For about the cost of a pizza, we were able to interface a FRS radio to the android phone, and the phone ran a program which polled its GPS, turned coordinates into NATO letter abbreviations, and spoke them through the speaker line. The FRS radio with VOX (voice operated transmit) sensed audio and transmitted accordingly. Although it worked very well, I later learned that this may not have been legal in the US because, although FRS doesn't require a user license and is legal to use anywhere as long as you use its stock antenna, I violated the rule that it cannot be operated above a certain height (20m I think?). Note that this should not be replicated, and probably shouldn't have been done in the first place. I know I'll take a lot of heat over this, but it's in the past now and will be done differently in the future.
Here are some photos right before the launch. It was a sunny day at the UF football stadium! The Android phone is taped the the outside of the box and takes pictures every few seconds, storing them on a micro SD card. Inside the box is an Arduino with GPS shield, and the FRS radio transmitter.
After launch the balloon ascended at a rate of about 500ft/min. It spat out GPS data often, and altitude (not encoded with NATO abbreviations) was the easiest to hear as I walked from the UF football stadium to the UF Gator Amateur Radio Club to use their equipment (namely an AZEL-rotor-controlled 70cm yagi antenna attached to an I-Com 706) to listen in as the balloon ascended... but not before a group photo!
Here we are in the station... let's get to work!
The results were a bit disappointing, as we believe the Android phone froze/crashed about 10,000 feet in the air! Since that was the device which generated the audio fed into the transmitter, when that phone died, the transmitter stopped transmitting, and we didn't hear anything else from the transmitter ever again! We included contact information in the payload and it's possible it will be found one day and we will be contacted about it. If this is the case, we'll view the SD cards and see the full GPS log and pictures from the edge of space! Until then, we can only cross our fingers and hope for the best. Either way we had a blast, and learned a lot along the way. Next time we can be better prepared for a solid recovery!
Here's audio of the device's last words when it was about 10,000 feet in the air: lastwords.mp3
Overall we had an awesome time! I'd like to thank everyone who helped with this project, especially UF students Richard, Kunal, Dante, and all of the SSTP high school students!
Markdown source code last modified on January 18th, 2021
---
title: High School Students' High Altitude Balloon #2
date: 2011-08-14 18:36:12
tags: amateur radio
---
# High School Students' High Altitude Balloon #2
__Last year a group of high school students,__ in collaboration with a seminar course on Space Systems sponsored by the University of Florida's [Student Science Training Program (SSTP)](http://www.cpet.ufl.edu/sstp/default.html), gained some real-world experience planning, building, and launching a research payload to the edge of space – all in a couple weeks! Last year's high altitude balloon launch was [covered on my website](http://www.swharden.com/blog/2010-07-14-high-altitude-balloon-transmitter/), and the radio transmitter I built for it was featured on [this Hack-A-Day post](http://hackaday.com/2010/07/27/200-mile-rf-transmitter-and-high-altitude-balloon/). Unlike last year's payload, whose only homebrew device was the radio transmitter, this year's payload had equipment we assembled ourselves, and instead of launching from NASA we launched from the UF football stadium! There were a couple problems along the way, and the payload hasn't been recovered (yet), but it was a fun project and we all learned a lot along the way!
**Update:** [project video](http://vimeo.com/27447092)
<div class="text-center img-border">
[](group.jpg)
</div>
Below is a panoramic photo right before the launch - see our balloon on the right? So cool!
<div class="text-center img-border">
[](pan.jpg)
</div>
__Our goal was to take photos from the edge of space, and log temperature, pressure, humidity, and GPS coordinates along the way.__ On-board were a radio transmitter, an Arduino with a GPS shield, and an Android phone to take pictures every few seconds.
__Android details:__ Most of the Android development was handled by UF student Richard along with high school students Benji, Tyler, Michael, and Kevin. Their GitHub project is here:<https://github.com/rich90usa/AndroidSensorLogger>. Also note that the automatic photo capture utilized [Photo Log Lite](http://www.appbrain.com/app/photo-log-lite/com.keepknocking.PhotoLogLite). We also used [GPSLogger](http://mendhak.github.com/gpslogger/") to handle logging GPS to SD. _"Both of these programs were chosen for their ability to run in the background - and do so reliably by using the 'correct' Android supported methods of doing so." -- Richard_
> Our code used the phone's text-to-speech engine to speak out an encoded version of every 90th new GPS coordinate. The data was encoded by connecting every number (0-9) to a word the [NATO phonetic alphabet](http://en.wikipedia.org/wiki/NATO_phonetic_alphabet). The code also used text-to-speech to have the phone speak out the phone's altitude data. --Benji
<div class="text-center img-border">
[](DSC_6013.jpg)
[](IMG_2095.jpg)
</div>
__The device consisted of 4 main components:__ a payload (the styrofoam box in which all of the electrical equipment was housed), a radar reflector (hanging off the bottom of the payload, to help make this object visible to aircraft), a parachute (at the top, made of bio-degradable plastic), and the balloon itself which measured about 6 feet wide when inflated at ground level (supposedly it reaches approximately 30 feet wide at high altitudes before it bursts). Once the balloon bursts, the parachute fills with air and the device floats back to earth.
<div class="text-center img-border">
[](DSC_6009.jpg)
</div>
__Kunal demonstrates the__ effectiveness of our parachute with a scientific "run test"!
<div class="text-center img-border">
[](DSC_6015.jpg)
</div>
__The radio communication system we used this year__ were a little more commercial than last year. Due to my limited time availability (I had an oral surgery rotation all week the week before launch), I chose to get something pre-packaged. My intent was to use FRS (those little 500mW family radio service radios) to send GPS data back to earth, but I later (after launch) did a little more research and realized that it probably wasn't the most legal way to do it. However, it was extremely cost effective (amateur radio transmitters and RF transmitter modules are quite pricey). For about the cost of a pizza, we were able to interface a FRS radio to the android phone, and the phone ran a program which polled its GPS, turned coordinates into NATO letter abbreviations, and spoke them through the speaker line. The FRS radio with VOX (voice operated transmit) sensed audio and transmitted accordingly. Although it worked very well, I later learned that this may not have been legal in the US because, although FRS doesn't require a user license and is legal to use anywhere as long as you use its stock antenna, I violated the rule that it cannot be operated above a certain height (20m I think?). Note that this should not be replicated, and probably shouldn't have been done in the first place. I know I'll take a lot of heat over this, but it's in the past now and will be done differently in the future.
<div class="text-center img-border">
[](DSC_6016.jpg)
[](DSC_6042.jpg)
[](DSC_6049.jpg)
[](DSC_6071.jpg)
</div>
__Here are some photos right before the launch.__ It was a sunny day at the UF football stadium! The Android phone is taped the the outside of the box and takes pictures every few seconds, storing them on a micro SD card. Inside the box is an Arduino with GPS shield, and the FRS radio transmitter.
<div class="text-center img-border img-small">
[](DSC_6079.jpg)
[](DSC_6119.jpg)
[](DSC_6132.jpg)
[](pan.jpg)
[](panZoomed.jpg)
[](DSC_6145.jpg)
</div>
__After launch the balloon ascended at a rate of about 500ft/min.__ It spat out GPS data often, and altitude (not encoded with NATO abbreviations) was the easiest to hear as I walked from the UF football stadium to the UF [Gator Amateur Radio Club](http://gatorradio.org) to use their equipment (namely an AZEL-rotor-controlled 70cm yagi antenna attached to an I-Com 706) to listen in as the balloon ascended... but not before a group photo!
<div class="text-center img-border">
[](DSC_6151.jpg)
</div>
__Here we are in the station... let's get to work!__
<div class="text-center img-border">
[](IMG_2118.jpg)
</div>
__The results were a bit disappointing,__ as we believe the Android phone froze/crashed about 10,000 feet in the air! Since that was the device which generated the audio fed into the transmitter, when that phone died, the transmitter stopped transmitting, and we didn't hear anything else from the transmitter ever again! We included contact information in the payload and it's possible it will be found one day and we will be contacted about it. If this is the case, we'll view the SD cards and see the full GPS log and pictures from the edge of space! Until then, we can only cross our fingers and hope for the best. Either way we had a blast, and learned a lot along the way. Next time we can be better prepared for a solid recovery!
__Here's audio of the device's last words__ when it was about 10,000 feet in the air: [lastwords.mp3](lastwords.mp3)
__Overall we had an awesome time!__ I'd like to thank everyone who helped with this project, especially UF students Richard, Kunal, Dante, and all of the SSTP high school students!
⚠️ WARNING: This article is obsolete
Articles typically receive this designation when the technology they describe is no longer relevant, code provided is later deemed to be of poor quality, or the topics discussed are better presented in future articles. Articles like this are retained for the sake of preservation, but their content should be critically assessed.
It's been my goal for quite some time to design a simple, easy-to-replicate transmitter for high altitude balloon telemetry transmission. I'm quite satisfied by what I came up with because it's very simple, cheap, easy to code for, and easy to change frequency. I'd say the most common alternative is a handheld amateur radio transmitter which starts around $60, requires an amateur radio license, and typically output 5W of FM on 144MHz (2m) or 440MHz (70cm). Fancier handheld radios are capable of transmitting APRS packets, and use established base station repeaters to listen to these frequencies, decode the packets, and update an internet database about current location information. Although it's quite fancy, elegant, and technical (and expensive), I desire a much simpler, cheaper, disposable option! If my balloon lands in the Atlantic ocean, I don't want to be out $100+ of radio equipment! This alternative is about $7.
Here's my solution. I don't normally build things on perf-board (I prefer sloppy Manhattan construction), but since this might go near the edge of space and be jerked around in turbulent winds, I figured it would be a nice and strong way to assemble it. Anyhow, it uses a can crystal oscillator as the frequency source. These things are pretty cool, because they're very frequency stable, even with changing temperatures.
The can oscillator (28.704MHz, selected to be in a rarely-used region of the 10m amatuer radio allocation which I'm licensed to use, call sign AJ4VD) outputs 5V square waves which I use to drive two successive class C amplifiers. The signal can be shunted to ground between the two stages by a third "control" transistor, which allows micro-controller control over the final amplifier. Although it may have seemed logical to simply supply/cut power from the oscillator to key the transmitter, I decided against it because that can oscillator takes 20ms to stabilize, and I didn't think that was fast enough for some encoding methods I wish to employ!
Although during my tests I power the device from my bench-top power supply (just a few LM3805 and LM3812 regulators in a fancy case), it's designed to be run off 3xAAA batteries (for logic) and a 9V battery (for the transmitter). I could have probably used a regulator to drop the 9V to 5V for the MCU and eliminated some extra weight, but I wonder how low the 9V will dip when I draw a heavy RF load? The 3xAAAs seemed like a sure bet, but quite at the expense of weight. I should consider the regulator option further... [ponders]
There's the device in action while it was in a breadboard. I've since wired it up in a perf board (pictured) and left it to transmit into a small string of wire inside my apartment as an antenna as I went to the UF Gator Amateur Radio Club (a few miles away) and tried to tune into it. It produced a stunningly beautiful signal! I can't wait for its first test on a high altitude balloon! Here it's transmitting CW Morse code the words "scott rocks", separated by appropriate call sign identification every 10 minutes, AJ4VD, my amateur radio license... of course!
Above is what the audio sounded like with a narrow CW filter (awesome, right?), and a 3KHz wide USB configuration. I think this should be more than enough to carry us through a mission, and aid in direction finding of a landed payload!
Notes about filtering: The output of this transmitter is quite harmonic-rich. The oscillator produces square waves for goodness' sake! The class C amplifier smooths a bit of that out, but you still need some low-pass filtering, not shown on the schematic. I think for my purposes a 3-pole Chebyshev filter will suffice, but just keep this in mind in case you replicate my design. You certainly don't want to be transmitting out of band! Below is the output of the transmitter viewed on my scope. It's suspiciously smooth, which leads me to wonder about the accuracy of my scope! I really should get a spectrum analyzer.
Markdown source code last modified on January 18th, 2021
---
title: High Altitude Balloon Transmitter Prototype
date: 2011-08-14 18:42:59
tags: amateur radio, circuit, old
---
# High Altitude Balloon Transmitter Prototype
__It's been my goal for quite some time__ to design a simple, easy-to-replicate transmitter for high altitude balloon telemetry transmission. I'm quite satisfied by what I came up with because it's very simple, cheap, easy to code for, and easy to change frequency. I'd say the most common alternative is a handheld amateur radio transmitter which starts around $60, requires an amateur radio license, and typically output 5W of FM on 144MHz (2m) or 440MHz (70cm). Fancier handheld radios are capable of transmitting [APRS](http://en.wikipedia.org/wiki/Automatic_Packet_Reporting_System) packets, and use established base station repeaters to listen to these frequencies, decode the packets, and update an internet database about current location information. Although it's quite fancy, elegant, and technical (and expensive), I desire a much simpler, cheaper, disposable option! If my balloon lands in the Atlantic ocean, I don't want to be out $100+ of radio equipment! This alternative is about $7.
<div class="text-center img-border">
[](DSCN1718.jpg)
</div>
__Here's my solution.__ I don't normally build things on perf-board (I prefer sloppy Manhattan construction), but since this might go near the edge of space and be jerked around in turbulent winds, I figured it would be a nice and strong way to assemble it. Anyhow, it uses a can crystal oscillator as the frequency source. These things are pretty cool, because they're very frequency stable, even with changing temperatures.
<div class="text-center img-border">
[](DSCN1701.jpg)
</div>
__The can oscillator (28.704MHz, selected to be in a rarely-used region of the 10m amatuer radio allocation which I'm licensed to use, call sign AJ4VD) outputs 5V square waves which I use to drive two successive class C amplifiers.__ The signal can be shunted to ground between the two stages by a third "control" transistor, which allows micro-controller control over the final amplifier. Although it may have seemed logical to simply supply/cut power from the oscillator to key the transmitter, I decided against it because that can oscillator takes 20ms to stabilize, and I didn't think that was fast enough for some encoding methods I wish to employ!
<div class="text-center img-border">
[](DSCN1717.jpg)
</div>
__Although during my tests I power the device from my bench-top power supply__ (just a few LM3805 and LM3812 regulators in a fancy case), it's designed to be run off 3xAAA batteries (for logic) and a 9V battery (for the transmitter). I could have probably used a regulator to drop the 9V to 5V for the MCU and eliminated some extra weight, but I wonder how low the 9V will dip when I draw a heavy RF load? The 3xAAAs seemed like a sure bet, but quite at the expense of weight. I should consider the regulator option further... [ponders]
__There's the device in action while it was in a breadboard.__ I've since wired it up in a perf board (pictured) and left it to transmit into a small string of wire inside my apartment as an antenna as I went to the UF Gator Amateur Radio Club (a few miles away) and tried to tune into it. It produced a stunningly beautiful signal! I can't wait for its first test on a high altitude balloon! Here it's transmitting CW Morse code the words "scott rocks", separated by appropriate call sign identification every 10 minutes, AJ4VD, my amateur radio license... of course!
* [cw.mp3](http://www.SWHarden.com/blog/images/cw.mp3)
* [usb.mp3](http://www.SWHarden.com/blog/images/usb.mp3)
__Above is what the audio sounded like__ with a narrow CW filter (awesome, right?), and a 3KHz wide USB configuration. I think this should be more than enough to carry us through a mission, and aid in direction finding of a landed payload!
__Notes about filtering:__ The output of this transmitter is quite harmonic-rich. The oscillator produces square waves for goodness' sake! The class C amplifier smooths a bit of that out, but you still need some low-pass filtering, not shown on the schematic. I think for my purposes a 3-pole [Chebyshev filter](http://en.wikipedia.org/wiki/Chebyshev_filter) will suffice, but just keep this in mind in case you replicate my design. You certainly don't want to be transmitting out of band! Below is the output of the transmitter viewed on my scope. It's suspiciously smooth, which leads me to wonder about the accuracy of my scope! I really should get a spectrum analyzer.
<div class="text-center img-border">
[](DSCN1707.jpg)
</div>
⚠️ WARNING: This article is obsolete
Articles typically receive this designation when the technology they describe is no longer relevant, code provided is later deemed to be of poor quality, or the topics discussed are better presented in future articles. Articles like this are retained for the sake of preservation, but their content should be critically assessed.
I was brainstorming some RF circuits today and I had the desire to create a rapid transmitter/receiver pair that anyone would have around their house. I decided that AM or FM radio would be good since everyone can receive that, and pondered how best to generate the necessary radio signal and modulate it appropriately. After a few LC oscillator designs, I thought about the RC oscillators built into most micro-controllers. I grabbed an ATMEL AVR I had on hand (an ATTiny44A) and checked the datasheet. It had an 8MHz RC oscillator, which could be divided-down to 1MHz, and output on a CKOUT pin - all configurable with a few hardware fuses! Note that commercial AM radio stations are between 0.52 and 1.61 MHz, so a 1MHz signal would be smack-dab in the middle of our radio dial! I had to build a prototype to see how well it would work. Once concern was that the RC oscillator wouldn't be stable enough to produce reliable audio - boy was I wrong!
__The circuitry is textbook simple.__ Appropriately configured, the AVR generates 5V square waves from its CKOUT pin. Although a pretty shape, they're not powerful enough on their own to be heard across a room, so I needed an amplifier stage. A class C amplifier provided by a 2n7000 is commonly done in the low power amateur radio (QRP) community, so I went with it. A 2n7000 N-channel MOSFET with a 220-ohm resistor on the drain and the CKOUT directly into the gate did a fine job (I've used this design for 10MHz QRSS transmitters before), and I was able to modulate its amplitude by feeding the voltage from a MCU pin (turned on/off rapidly) through a decoupling capacitor into the drain of the MOSFET. I couldn't have asked for a simpler result!
This code sends a message in Morse code. It seems too easy! Applications are endless, as this is one heck of an easy way to send audio from a micro-controller to a radio, and possibly to a computer. Morse code is easy, and since we have the ability to dynamically generate different audio frequencies and tones, data exchange is easy too! Nothing's stopping you from adding the code to turn this into a RTTY (or Hellschreiber?) transmitter.
Again, this transmitter can be heard on a standard AM radio tuned to about 1000 kHz. This is the setup I used with great success:
Here's the code on the chip! Nothing complicated:
// designed for and tested with ATTiny44A
#include <avr/io.h>
#define F_CPU 1000000UL
#include <avr/delay.h>
#include <avr/interrupt.h>
void beep(){
for(char i=50;i;i--){
DDRA|=_BV(PA7);_delay_ms(1);
DDRA&=~_BV(PA7);_delay_ms(1);
}
}
void rest(){_delay_ms(100);}
void dot(){beep();rest();}
void dash(){beep();beep();beep();rest();}
void space(){rest();rest();}
void space2(){space();space();}
int main(){
DDRA|=_BV(PA7);
for(;;){
dot();dot();dot();space(); // S
dash();dot();dash();dot();space(); // C
dash();dash();dash();space(); // O
dash();space(); // T
dash();space(); // T
space2();
dot();dash();dot();space(); // R
dash();dash();dash();space(); // O
dash();dot();dash();dot();space(); // C
dash();dot();dash();space(); // K
dot();dot();dot();space(); // S
_delay_ms(1000); // silence
}
return 0;
}
THIS IS ILLEGAL to do if you exceed a certain amount of power because you're stepping on legitimate commercial broadcasters and will have to deal with the FCC. Additionally, you are transmitting on more frequencies than the primary frequency because the signal is heavy in odd harmonics. This means a 1 MHz transmitter, producing square waves, will generate tones on 1, 3, 5, 7 MHz, etc. Don't do this with much power! Heck, you probably shouldn't do it at all ;-)
Markdown source code last modified on January 18th, 2021
---
title: Ridiculously Simple AVR AM Radio Transmitter
date: 2011-08-06 19:32:44
tags: amateur radio, circuit, old
---
# Ridiculously Simple AVR AM Radio Transmitter
__I was brainstorming some RF circuits today__ and I had the desire to create a rapid transmitter/receiver pair that anyone would have around their house. I decided that AM or FM radio would be good since everyone can receive that, and pondered how best to generate the necessary radio signal and modulate it appropriately. After a few LC oscillator designs, I thought about the RC oscillators built into most micro-controllers. I grabbed an ATMEL AVR I had on hand (an ATTiny44A) and checked the datasheet. It had an 8MHz RC oscillator, which could be divided-down to 1MHz, and output on a CKOUT pin - all configurable with a few hardware fuses! Note that commercial AM radio stations are between 0.52 and 1.61 MHz, so a 1MHz signal would be smack-dab in the middle of our radio dial! I had to build a prototype to see how well it would work. Once concern was that the RC oscillator wouldn't be stable enough to produce reliable audio - boy was I wrong!
<div class="text-center img-medium">
[](schem.jpg)
</div>
__The circuitry is textbook simple.__ Appropriately configured, the AVR generates 5V square waves from its CKOUT pin. Although a pretty shape, they're not powerful enough on their own to be heard across a room, so I needed an amplifier stage. A class C amplifier provided by a 2n7000 is commonly done in the low power amateur radio (QRP) community, so I went with it. A 2n7000 N-channel MOSFET with a 220-ohm resistor on the drain and the CKOUT directly into the gate did a fine job (I've used this design for 10MHz QRSS transmitters before), and I was able to modulate its amplitude by feeding the voltage from a MCU pin (turned on/off rapidly) through a decoupling capacitor into the drain of the MOSFET. I couldn't have asked for a simpler result!
__This code sends a message in Morse code.__ It seems too easy! Applications are endless, as this is one heck of an easy way to send audio from a micro-controller to a radio, and possibly to a computer. Morse code is easy, and since we have the ability to dynamically generate different audio frequencies and tones, data exchange is easy too! Nothing's stopping you from adding the code to turn this into a RTTY (or [Hellschreiber?](http://www.swharden.com/blog/2011-08-05-i-before-e-except-after-hellschreiber/)) transmitter.
<div class="text-center img-border">
[](DSCN1670.jpg)
</div>
__Again, this transmitter can be heard on a standard AM radio tuned to about 1000 kHz.__ This is the setup I used with great success:
<div class="text-center img-border">
[](schem2.jpg)
</div>
__Here's the code on the chip!__ Nothing complicated:
```c
// designed for and tested with ATTiny44A
#include <avr/io.h>
#define F_CPU 1000000UL
#include <avr/delay.h>
#include <avr/interrupt.h>
void beep(){
for(char i=50;i;i--){
DDRA|=_BV(PA7);_delay_ms(1);
DDRA&=~_BV(PA7);_delay_ms(1);
}
}
void rest(){_delay_ms(100);}
void dot(){beep();rest();}
void dash(){beep();beep();beep();rest();}
void space(){rest();rest();}
void space2(){space();space();}
int main(){
DDRA|=_BV(PA7);
for(;;){
dot();dot();dot();space(); // S
dash();dot();dash();dot();space(); // C
dash();dash();dash();space(); // O
dash();space(); // T
dash();space(); // T
space2();
dot();dash();dot();space(); // R
dash();dash();dash();space(); // O
dash();dot();dash();dot();space(); // C
dash();dot();dash();space(); // K
dot();dot();dot();space(); // S
_delay_ms(1000); // silence
}
return 0;
}
```
___THIS IS ILLEGAL__ to do if you exceed a certain amount of power because you're stepping on legitimate commercial broadcasters and will have to deal with the FCC. Additionally, you are transmitting on more frequencies than the primary frequency because the signal is heavy in odd harmonics. This means a 1 MHz transmitter, producing square waves, will generate tones on 1, 3, 5, 7 MHz, etc. Don't do this with much power! Heck, you probably shouldn't do it at all ;-)_
