We Love and Will Miss You, Angelina
Posted on August 23rd, 2011 1:08:43 AM |
480 words | 16 Comments
Filed under: General |
Scott was 25.91 years old when he wrote this
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 your outpouring of support and encouragement is such a blessing to us all.
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.
The following are videos of a few of the songs sung at Angelina’s memorial service in Gainesville, FL. Anelisse Martinez (a dental school classmate, and friend of Angelina and me) sang to an instrumental version of closer walk with thee and
gravity. For the last song, she was accompanied by Dennis Beliveau (another dental school classmate, and friend of Angelina and me) singing the prayer. 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 truly blessed to be surrounded by so many wonderful people.
Many people have been sharing memories and photos through Facebook, and if you have anything you wish to share I encourage you to do so. I ask for your continued prayer for Angelina’s family, her friends, and me – Angelina and I loved each other so much, and her passing is hard for everyone who knew her. Thank you for your kindness.
» 16 Comments!
High Altitude Balloon Transmitter Prototype
Posted on August 14th, 2011 6:42:59 PM |
881 words | 3 Comments
Filed under: General |
Scott was 25.89 years old when he wrote this
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!
DOWNLOAD: cw.mp3
DOWNLOAD: 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 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.
» 3 Comments!
High School Students’ High Altitude Balloon #2
Posted on August 14th, 2011 6:36:12 PM |
1,815 words | 3 Comments
Filed under: General, Microcontrollers, Radio, high altitude balloon |
Scott was 26.35 years old when he wrote this
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!
Untitled from DJ Meyers on Vimeo.
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.
The balloon is ready to be inflated!
The balloon is about 75% inflated at this point.
Richard looking all serious as he finishes inflating the balloon.
…panoramic above, zoomed below…
What a cool photo! It needs no words to describe!
The balloon is way up there!
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:
DOWNLOAD 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!
» 3 Comments!
Ridiculously Simple AVR AM Radio Transmitter
Posted on August 6th, 2011 7:32:44 PM |
749 words | 7 Comments
Filed under: General |
Scott was 25.87 years old when he wrote this
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 
» 7 Comments!
I before E except after Hellschreiber
Posted on August 5th, 2011 6:52:40 PM |
1,960 words | 10 Comments
Filed under: C/C++, Circuitry, Microcontrollers, Radio, high altitude balloon |
Scott was 25.86 years old when he wrote this
| This post describes a project I designed which transmits strings of data from a microcontroller to a PC’s screen using audio beeping in a special mode called Hellschreiber. Although these days it’s almost exclusively used by amateur radio operators, I thought it would make a cool microcontroller project! The result can be accomplished with a microcontroller and a speaker as a transmitter and a PC with a microphone as a receiver and decoder, or with actual radio equipment (even toy walkie talkies) by transmitting the tones over modulated radio frequencies for long distance communication! Ideas anyone?
SPECIAL THANKS: I’d like to think Mike Seese for his brainstorming help in making this project a reality. Mike and I are working on a high altitude balloon project together, and a creative inexpensive radio link is one of our goals. Thanks Mike! |
As a professional dental student by day and amateur electrical/RF engineer by night, I’m having a very strange summer. I’m developing rapidly in my experience and skills in both arenas. I finally feel like I have a working knowledge of most fundamental electrical and radio frequency concepts, and I’m starting to see patients and do procedures on humans (no more mannequins) in the student dental clinic. For legal and ethical reasons I do not write specifics about what I do with my patients, but I certainly make up for it by documenting the electronic projects I work on! My goals of doing this are to (a) inspire potential electronics tinkerers to come up with new ideas and attack new projects, and (b) receive feedback and insight from those more experienced than me to help me grow in my knowledge. My eye caught a comment a few posts ago that made me smile: You have been blessed with talent and the drive to attempt things not been tried before, keep it up, great job. –David S While I can’t claim that everything I do is truly novel or never tried before, I appreciate the encouraging words. Thank you David S!
Today’s project is a fun one involving vintage wartime radio equipment, amateur radio computer software, and a healthy dose of microcontrollers! My goal is to design a single chip Hellschreiber (technically Feldhellschreiber) transmitter. “Hellschreiber” translates into English as “Light Writer” and is a pun on the name of its inventor, Rudolf Hell, who built the first device in 1920. It was intended to allow messages to be transferred over poor radio links too noisy for intelligible voice or radioteletype (RTTY) communication. Its cool factor is upped by the fact that it was sometimes used by the German military in conjunction with the Enigma encryption system during World War 2! [As an aside, RTTY is still pretty sweet and dates back to the mid 1800s! Check out hardware receivers in video 1 and video 2]
Seeing a battlefield-ready Hellschreiber receiver gives you a good idea of how it works. (The video isn’t mine, I found it on youtube.) The concept is relatively simple (shown above), and the receiver has only 2 moving parts. A spinning corkscrew presses a ticker tape into ink when it receives a radio signal. As the radio signal beeps on and off, the corkscrew contacts at different positions at different times, and letters are written on the ticker tape! 
The designers of these things were extraordinarily creative! The picture on the right shows a Hellschreiber transmitter – basically a typewriter with mechanical wizardry that turns key presses into a series of radio tones corresponding to the pixelated shape of a character.
Almost a century later, people are still sending messages around the world using Hellschreiber! With an amateur radio license and an amateur radio transceiver you can tune around special Hellschreiber calling frequencies and engage in conversations with other people who enjoy using this unique mode. Computers have modernized the process, allowing you to send Hellschreiber text by typing on your keyboard and receive it by just looking at your screen. My favorite program (free) to do this is Digital Master 780, part of Ham Radio Deluxe.
This is the project I just completed. It takes strings of text stored (or dynamically generated) in an array on a microcontroller (I’m using an ATMega48, but the code is almost identical for any ATMEL AVR microcontroller, and easy adapted for other architectures) and turns it into an audio tone using PWM. This audio tone could be fed into a speaker and a microphone across the room could receive it and use the software to show the received data, or the audio could be fed into a radio transmitter and a PC hooked to the receiver could decode the audio. Either way, the text in the microcontroller is converted to Hellschreiber audio tones ready to be used however you see fit! Although I designed it as a resilient way to transmit GPS/altitude data from a high altitude balloon using a small, cheap, low-power radio transmitter, this project is just the foundation of a plethora of potential projects!
Here’s the circuit I’m using. It’s actually less complicated than shown – all those yellow wires are going to my AVR programmer! The chip just receives +5V and GND, and the audio is generated automatically and output on the OC0A pin, which happens to be pin 12 on my ATMega48. The output (audio level square waves) is fed to a crystal oscillator like this one, which generates square waves with an amplitude equal that to the input. Thus, by audio-frequency AC from the microchip, decoupled through a series capacitor, added to the power supply of the oscillator (provided by the 5V rail through a 1.8k resistor), we effectively produce an amplitude modulated (AM) radio signal!
This is the receiver I’m using. I’m lucky enough to have an all-mode, general-coverage, 100W amateur radio transceiver! It’s a Yaesu 857-D and I’m completely in love with it. It’s quite pricey though! You can find wide coverage receive-only radios called radio scanners (or police scanners), often for $20 or so on eBay which would do just as good a job of receiving all sorts of radio signals! Whatever you use, after tuning into the audio with the ham radio delux software, you’ll be able to decode Hellschreiber like this:
A few notes about the code: Each letter is sent twice vertically and I don’t think I should have done that. It’s easy enough to correct by eliminating the second FOR loop in the sendChar() function, and doubling the height of the pixels transmitted by changing on(1) and off(1) to on(2) and off(2). Then again, I could be mistaken – I don’t use this mode much. Also, horizontal width of characters (increase this and horizontally compress the received image to reduce the effects of noise) is controlled by a single variable, dynamically adjustable in software. Characters are created from a 3×5 grid (15 bits) and stored as an integer (16 bits, 2 bytes in AVR-GCC). Custom characters are certainly possible! This program takes 16.1% of program space (658 bytes) and 25.4% of data space (130 bytes) and certainly leaves room for optimization.
// designed for and tested with ATMega48
#include <avr/io.h>
#define F_CPU 8000000UL
#include <avr/delay.h>
#include <avr/interrupt.h>
/*
character format (3x5):
KFA
LGB
MHC
NID
OJE
variable format:
2-byte, 16-bit int 0b0ABCDEFGHIJKLMNO
(note that the most significant bit is not used)
*/
#define A 0b0111111010011111
#define B 0b0010101010111111
#define C 0b0100011000101110
#define D 0b0011101000111111
#define E 0b0100011010111111
#define F 0b0100001010011111
#define G 0b0100111000101110
#define H 0b0111110010011111
#define I 0b0100011111110001
#define J 0b0111110000100011
#define K 0b0110110010011111
#define L 0b0000010000111111
#define M 0b0111110110011111
#define N 0b0011111000001111
#define O 0b0011101000101110
#define P 0b0010001010011111
#define Q 0b0111011001011110
#define R 0b0010111010011111
#define S 0b0100101010101001
#define T 0b0100001111110000
#define U 0b0111110000111111
#define V 0b0111100000111110
#define W 0b0111110001111111
#define X 0b0110110010011011
#define Y 0b0110000011111000
#define Z 0b0110011010110011
#define n0 0b0111111000111111
#define n1 0b0000011111101001
#define n2 0b0111011010110111
#define n3 0b0111111010110001
#define n4 0b0111110010011100
#define n5 0b0101111010111101
#define n6 0b0101111010111111
#define n7 0b0110001011110000
#define n8 0b0111111010111111
#define n9 0b0111111010111101
#define SP 0b0000000000000000
#define BK 0b0111111111111111
#define SQ 0b0001000111000100
#define PR 0b0000110001100011
#define AR 0b0001000111011111
volatile char width=1; // width of characters, widen to slow speed
#define spd 8300 // synchronization, incr to make it slant upward
void rest(char times){while (times){times--;_delay_us(spd);}}
void on(char restfor){OCR0A=110;rest(restfor);}
void off(char restfor){OCR0A=0;rest(restfor);}
void sendChar(int tosend){
char w;
char bit;
for(w=0;w<width*2;w++){ // left column
off(1);
for (bit=0;bit<5;bit++){
if ((tosend>>bit)&1) {on(1);}
else {off(1);}
}
off(1);
}
for(w=0;w<width*2;w++){ // middle column
off(1);
for (bit=5;bit<10;bit++){
if ((tosend>>bit)&1) {on(1);}
else {off(1);}
}
off(1);
}
for(w=0;w<width*2;w++){ // right column
off(1);
for (bit=10;bit<15;bit++){
if ((tosend>>bit)&1) {on(1);}
else {off(1);}
}
off(1);
}
off(14); // letter space (1 column)
}
// CUSTOMIZE THE MESSAGE, OR GENERATE IT DYNAMICALLY!
int message[]={AR,AR,AR,S,W,H,A,R,D,E,N,PR,C,O,M,SP,R,O,C,K,S,
SP,AR,AR,AR,SP,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,
V,W,X,Y,Z,n0,n1,n2,n3,n4,n5,n6,n7,n8,n9,BK,SP};
void sendMessage(){
char i;
for(i=0;i<sizeof(message)/2;i++){
sendChar(message[i]);
}
}
int main(){ // ### PROGRAM STARTS HERE ###
// this sets up CPWM in CTC mode,
// it may be slightly different for other chips
DDRD|=255; // OC0A is now an output
TCCR0A=0b01000010; // toggle on match, CTC mode
TCCR0B=0B00000011; // set prescalar
for(;;){
width=1; // fast mode
sendMessage();
width=3; // slow mode
sendMessage();
}
return 0;
}
» 10 Comments!
PC/microcontroller “wireless” data transfer (part 2)
Posted on July 31st, 2011 10:35:12 PM |
880 words | 1 Comment
Filed under: General |
Scott was 25.85 years old when he wrote this
MULTI-POST PROJECT >>> [view PART 1 for circuity and theory]
Last week I had the crazy idea of sending data from a PC to a microchip through the monitor, using javascript and a web interface as a ridiculously simple data transfer platform that would work on virtually any computer! While I quickly hacked together the hardware, I struggled with the web interface (I’m a little slow with javascript) and I got a lot of help from people around the internet, especially after my project (and need for assistance) was mentioned on Hack-A-Day!
This is part two of a multi-page project. To fully understand what I’m trying to accomplish and why I want to accomplish it, read the first part of the project.
Finally, I have a working javascript! I’d like to thank Tom, Riskable, Ben, and Mike for their input on this script. We got it to a point where we think it’s friendly to the majority of browsers and platforms. The idea is simple – enter two bytes to send the chip, it generates it’s own checksum (an XOR of the two bytes), and it flashes it out. Here’s a photo of the interface, click it for a live demo:
Here’s the code that goes on the microchip:
#include <stdlib.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
#define F_CPU 12000000UL
#include <util/delay.h>
#include "lcd.h"
#include "lcd.c"
volatile int times=1000;
char readADC(char pin){
ADMUX = 0b1100000+pin; // AVCC ref on ADC5
ADCSRA = 0b10000111; //ADC Enable, Manual Trigger, Prescaler 128
ADCSRA |= (1<<ADSC); // reset value
while (ADCSRA & ( 1<<ADSC)) {}; // wait for measurement
return ADCH;
}
int main(void)
{
lcd_init(LCD_DISP_ON);
char lastClock=0;
char thisClock=0;
char thisClock2=0;
char thisData=0;
char buffer[8];
char lastNum=0;
char bitsGotten=0;
int msInactive=0;
/*for(;;){
itoa(readADC(5), buffer, 10);
lcd_gotoxy(0,15);
lcd_puts(buffer);
itoa(readADC(4), buffer, 10);
lcd_gotoxy(8,0);
lcd_puts(buffer);
}*/
for(;;){
thisClock = readADC(5);
if (thisClock<250){
_delay_ms(1);
if (readADC(5)>250) {break;}
_delay_ms(1);
if (readADC(4)<250) {thisData=1;}
else {thisData=0;}
lastNum=lastNum*2+thisData; // left shift, add data
itoa(thisData, buffer, 10);
lcd_puts(buffer);
msInactive=0;
bitsGotten++;
if (bitsGotten==8){
lcd_gotoxy(1,1);
lcd_puts("= ");
lcd_gotoxy(2,1);
itoa(lastNum, buffer, 10);
lcd_puts(buffer);
bitsGotten=0;
lastNum=0;
lcd_gotoxy(0,0);
}
while (1) {
if (readADC(5)>250){
_delay_ms(10);
if (readADC(5)>250){break;}
}
}
}
else{
msInactive++;
if (msInactive==400){
bitsGotten=0;
lastNum=0;
lcd_clrscr();
lcd_puts(" TIMEOUT");
_delay_ms(1000);
lcd_clrscr();
lcd_gotoxy(0,0);
lcd_puts("________ =");
lcd_gotoxy(0,0);
}
}
_delay_ms(1);
}
}
Here’s the javascript in a web page:
<html>
<head>
<style>
.flasher {
font-weight: bold;
text-align: center;
color: #888888;
width: 200px;
height: 200px;
background-color: black;
float: left;
-webkit-transform: translateZ(0);
border-right-style:dotted;
border-color:#888888;
border-width:1px;
}
</style>
<script type="text/javascript">
/* Copyright 2011, Tom Hayward <tom@tomh.us>, MIT License */
var ms = 50,
bytes = 0,
leftblock = null,
rightblock = null,
statustext = null;
function sendBit(bit) {
if (bit) {rightblock.style.backgroundColor = 'white';}
else {rightblock.style.backgroundColor = 'black';}
leftblock.style.backgroundColor = 'white';
setTimeout(function() {
leftblock.style.backgroundColor = 'black';
rightblock.style.backgroundColor = 'black';
}, ms);
}
function sendByte(byte) {
var bits = 8;
setTimeout(function() {
var timer = setInterval(function() {
bits--;
sendBit(byte >> bits & 1);
if (bits == 0) {clearInterval(timer);return;}
}, ms * 2);
}, ms * 2 * bits * bytes++);
}
function Pause() {
timer = setTimeout("endpause()",5000); // 3 secs
return false;
}
function endpause() {
sendData();
return false;
}
function sendData() {
var button = document.getElementById('sendnow'),
byte1 = parseInt(document.getElementById('b1').value),
byte2 = parseInt(document.getElementById('b2').value),
checksum = byte1 ^ byte2;
leftblock = document.getElementById('leftblock');
rightblock = document.getElementById('rightblock');
statustext = document.getElementById('status');
bytes = 0; // reset byte counter
document.getElementById('b3').value = checksum;
button.disabled = true;
statustext.innerHTML = "Writing data...";
sendByte(byte1);
sendByte(byte2);
sendByte(checksum);
setTimeout(function() {
statustext.innerHTML = "done";
button.disabled = false;
}, ms * 2 * 8 * bytes);
}
</script>
</head>
<body bgcolor="#666">
<h1>PC/MCU Flasher Interface</h1>
<code>
Byte 1: <input id="b1" type="text" name="b1" size="3" value="255" /> <br>
Byte 2: <input id="b2" type="text" name="b2" size="3" value="0" /> <br>
CHKsum: <input id="b3" type="text" name="b3" size="3" value="" disabled="disabled" /> <br>
<br>
<input id="sendnow" type="button" value="SEND NOW" onClick="javascript:Pause();" />
<br><br><br>
<p>Status: <span id="status"></span></p>
</code>
<div id="leftblock" class="flasher"> CLOCK</div>
<div id="rightblock" class="flasher"> DATA</div>
</body>
</html>
|
» 1 Comment so far...
PC/microcontroller “wireless” data transfer (part 1)
Posted on July 26th, 2011 10:35:16 PM |
813 words | 2 Comments
Filed under: C/C++, Circuitry, General, Microcontrollers |
Scott was 25.84 years old when he wrote this
UPDATE! >>> [FINISHED PROJECT HERE]
Several days ago I had a crazy idea. I was driving to Orlando to pick my wife up from the airport and it was dark and stormy on the highway and I was thinking about the backlash I got from my Sound Card Microcontroller/PC Communication project, where I used an embarrassingly simple hardware to accomplish the simple task of exchanging a few bytes of data between a PC and microcontroller (in the face of many people who adamantly prefer more complicated “traditional standard” methods). The car in front of me drove with his emergency flashers on, and at times all I could see were his lights. At that moment the crazy idea popped in my head – I wonder if I could use a PC monitor and phototransistors to send data to a microchip? I can’t think of any immediate uses for this capability, but perhaps if I make a working prototype I’ll stumble upon some. Either way, it sounds like a fun project!
The circuit is as simple as it gets. 
A phototransistor is exactly what it says, a photo (light-triggered) transistor (uses small current to trigger a large current). It’s a photodiode with a small transistor circuit built in. Make sure you give it right polarity when you plug it in! For some reason (likely known to electrical engineers, not dental students) the larger metal piece in the plastic part, which I normally associate as negative for LEDs, should be plugged in the +5V for my photodiode. Again, make sure you hook yours up right. I purchased mine from eBay quite cheaply, but I’ll bet you can find some in RadioShack. Note that the value of the 22k resistor is important, and that your needed value may differ from mine. The resistor relates to sensitivity, the larger the value the more sensitive the device is to light. If it’s too sensitive, it will sense light even when aimed at a black portion of the screen.
Initial tests were done using the pins as digital inputs. This was difficult to achieve because, even as transistorized photo-diodes, it took a large difference in light to go from 5V to 0V (even past the 2.5V threshold). After a few minutes of frustration, I decided to use ADC to measure the light intensity. I use only the most significant 8 bits (ADCH). I found that in ambient light the readings are 255, and that white monitor light is around 200. Therefore my threshold is 250 (4.88V?) and I use this for logic decisions. Here’s my setup showing the ADC value of each phototransistor translated into a 1 and 0 for clock (C) and data (D). Both are aimed toward the lamp, so both show a logical 1:
My first test involved reading the data from the image above. The clock is on the bottom line, data is on the top. Every time the clock transitions from black to white, the value of the data at that point is read (white=1, black=0) and the number is placed on a screen. Here’s what it looks like in action:
Hopefully soon we can get a JavaScript interface going! Rather than swiping I’d like to just point this at the screen and let JS flash some squares for my device to read. This will allow virtually unlimited amounts of data to be transferred, albeit slowly, to the micro-controller. Here’s a preliminary sketch of how to send strings.
Remember now we’re using a time domain, not a 2d barcode. I really stink at writing JavaScript, I’m going to have to pull in some help on this one!
» 2 Comments!
Frequency Counter Gen2
Posted on July 24th, 2011 5:07:24 PM |
667 words | 4 Comments
Filed under: C/C++, Circuitry, General, Microcontrollers, Python, Radio |
Scott was 25.83 years old when he wrote this
I’m working to further simplify my frequency counter design. This one is simpler than my previous design both in hardware and software! Here’s a video to demonstrate the device in its current state:
I utilize the ATMega48’s hardware counter which is synchronous with the system clock, so it can only measure frequency less than half of its clock speed. I solve this issue by dividing the input frequency by 8 and clocking the chip at 12mhz. This allows me to measure frequencies up to about 48MHz, but can be easily adapted to measure over 700MHz (really?) by dividing the input by 128. Division occurs by a 74HC590 8-bit counter (not a 74HC595 as I accidentally said in the video, which is actually a common shift register), allowing easy selection of input divided by 1, 2, 4, 8, 16, 32, 64, or 128. The following image shows the o-scope showing the original signal (bottom) and the divided-by-8 result (top)
The device outputs graphically to a LCD simply enough. That LCD is from eBay and is only $3.88 shipped! I’m considering buying a big box of them and implementing them in many more of my projects. They’re convenient and sure do look nice!
The signal I test with comes from an oscillator I built several months ago. It’s actually a SA612 style receiver whose oscillator is tapped, amplified, and output through a wire. It’s tunable over almost all of 40m with a varactor diode configuration. It was the start of a transceiver, but I got so much good use out of it as a function generator that I decided to leave it like it is!
THIS IS HOW THE PROGRAM WORKS: I don’t supply a schematic because it’s simple as could be. Divide the input frequency to something relatively slow, <1MHz at least. Configure the 16-bit counter to accept an external pin as the counter source (not a prescaled clock, as I often use in other applications). Then set the timer value to 0, _delay_ms() a certainly amount of time (1/10th second), and read the counter value. Multiply it by 10 to account for the 1/10th second, then multiply it by 8 to account for the divider, and it’s done! It will update 10 times a second, with a resolution down to 10*8 = 80 Hz. It’s well within the range of amateur radio uses! If you’re considering replicating this, read up on how to use hardware counters with ATMEL AVR microcontrollers. That should be enough to get you started! Here’s the code I used…
For the LCD, this code requires LCD library.
#include <stdlib.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
#include <util/delay.h>
#include "lcd.h"
#include "lcd.c"
int main(void)
{
TCCR1B=0b00000111; // rising edge trigger
char buffer[8];
long toshow=0;
char mhz=0;
int khz=0;
int hz=0;
lcd_init(LCD_DISP_ON);
for(;;){
lcd_clrscr();
lcd_gotoxy(0,0);
itoa(mhz , buffer, 10);
lcd_puts(buffer);
lcd_puts(".");
if (khz<100){lcd_puts("0");}
itoa(khz , buffer, 10);
lcd_puts(buffer);
itoa(hz/100 , buffer, 10);
lcd_puts(buffer);
lcd_puts(" MHz");
TCNT1=0;
_delay_ms(99);
_delay_us(312);
toshow=TCNT1;
toshow=(long)toshow*16*10; // tenth second period
mhz=toshow/1000000;
toshow=toshow-mhz*1000000;
khz=toshow/1000;
toshow=toshow-khz*1000;
hz=toshow;
}
}
» 4 Comments!
Half-Hearted DIY Logic Analyzer Works, a Little
Posted on July 16th, 2011 10:52:17 PM |
824 words | 4 Comments
Filed under: Circuitry, General, Microcontrollers, Python |
Scott was 25.81 years old when he wrote this
While trying to attack the problem described in the previous entry, it became clear that a logic analyzer would be necessary. I thought I’d try to build one, and my first attempt was so close to being successful, but not quite there. It records 19 channels (the maximum pins available on the ATMega48 not being occupied by the status LED or USB connection pins) at a rate just under 1,000 samples per second. The USB connection to the PC is obvious, and it utilizes the V-USB project to bit-bang the USB protocol. I’m posting this in part because some of the comments to my entry two posts ago were disheartening, discouraging, and even down-right viscous! I made a simple way to send numbers to a PC through the sound card, so what? Don’t be nasty about it! Meh, internet people. Anyway, here’s a marginally more proper way to send data to a PC with USB and an AVR (logging and interface designed in python), but I’ll probably still get yelled at for it.
As you can see from the video, it’s good but not good enough. If I could get samples at 2,000 per second I’d probably be OK, but it’s just not quite fast enough with it’s current, ultra-simplistic method of sample recording. I’ll figure out a fancier way to build a spectrum analyzer – it’s obvious the platform is there, it just needs some refinement.
A few stills:
UPDATE! The more I think about it, the more I think this might be just good enough to work! Look at the stagger in those peaks near the top – that’s probably the lines telling which character to display. Data between the peaks indicates the value to be provided, and I should have enough time to accurately measure that… Maybe this is good enough after all? I’ll have to run some more tests tomorrow…
Where’s the code? It kills me to do this, but I need to withhold the chip side code. I’m working on an idiot’s guide to USB connectivity with AVR microcontrollers, and I’d rather post the simplest-case code first, then share complicated stuff like this. I’ll post the python scripts:
# LOGIC.PY - this script will log (or print) raw data from the USB device
from optparse import OptionParser
import time
import usb.core
import usb.util
import os
while True:
print "\nTrying to communicate with the Gator Keyer ...",
dev = usb.core.find(find_all=True, idVendor=0x16c0, idProduct=0x5dc)
if len(dev)==0: print "FAIL"
dev=dev[0]
dev.set_configuration()
print "there it is!"
break
def readVals():
x=dev.ctrl_transfer(0xC0, 2, 2, 3, 4).tolist()
return x
def toBinary(desc):
bits=[]
for i in range(7,-1,-1):
if (2**i>desc):
bits.append('0')
else:
bits.append('1')
desc=desc-2**i
return bits
def toStr(lists):
raw=[]
for port in lists: raw+=toBinary(port)
return ''.join(raw)
### PROGRAM START ##################
live=False
#live=True
start=time.time()
if live==True:
while True:
a,b,c,d=readVals()
if not a==123: continue #bad data
elapsed=time.time()-start
print "%.010f,%s"%(elapsed,toStr([b,c,d]))
else:
times=0
data=''
f=open("out.txt",'a')
while True:
a,b,c,d=readVals()
if not a==123: continue #bad data
elapsed=time.time()-start
data+="%.010f,%s\n"%(elapsed,toStr([b,c,d]))
times+=1
if times%1000==999:
print "%d readings / %.02f = %.02f /sec"%(times,elapsed,times/elapsed)
f.write(data)
data=""
#logicGraph.py - this will show the data in a pretty way
import matplotlib.pyplot as plt
import numpy
c={
0:"",
1:"",
2:"blk sol",
3:"yel str",
4:"yel sol",
5:"pur sol",
6:"pur str",
7:"",
8:"",
9:"",
10:"blu sol",
11:"blu str",
12:"orn sol",
13:"orn str",
14:"pnk sol",
15:"pnk str",
16:"",
17:"",
18:"",
19:"",
20:"",
21:"",
22:"",
23:"",
24:"",
}
print "loading"
f=open("out.txt")
raw=f.readlines()
f.close()
print "crunching"
times=numpy.array([])
data=numpy.array([])
for line in raw:
if len(line)<10: continue
line=line.replace("\n",'').split(',')
times=numpy.append(times,float(line[0]))
bits = []
for bit in line[1]:
if bit=="1":bits.append(1)
else:bits.append(0)
data=numpy.append(data,bits)
columns=24
rows=len(data)/columns
data=numpy.reshape(data,[rows,columns])
print "DONE processing",len(data),"lines\n\n"
print "plotting..."
plt.figure()
plt.grid()
for i in range(len(c.keys())):
if c[i]=="": continue
plt.plot(times,data[:,i]+i*1.1,'-',label=c[i])
plt.legend()
plt.show()
» 4 Comments!
Frequency Counter Hacked to add USB Functionality
Posted on July 11th, 2011 5:02:33 PM |
2,649 words | 4 Comments
Filed under: Circuitry, General, Microcontrollers, Radio |
Scott was 25.79 years old when he wrote this
| This is a multi-part blog entry added over 2 days of time documenting the progress of the addition of USB to a simple frequency counter. The final result lets me graph frequency over time on the computer, automatically, over days of time if desired. I’m quite pleased at the result, especially considering so little circuitry was required! Although this page documents all the way from conception to completion, if you wish you can jump straight to the final product. |
It looks like this will be a multi-part blog entry. I’m in the process of figuring out how to add USB functionality to this simple device, which will be a fun way for me to express my creativity and think a bit outside the box while gaining some simple electrical engineering experience! Here’s the jist of what I’m planning…
After a brief trip to Orlando to visit family, I decided to stop by the house of one of my neighbors who worked at the same small engineering company I did when I was first starting college (about the time I decided to peruse biology rather than engineering). I hadn’t seen him in a while and we talked about various electronics things (he’s working on an impressive project currently), and before I left he offered me a brown box. “Do you have any use for a function generator?” I got excited and said “sure!” On closer inspection, it was actually a frequency counter, and he said “oh well I don’t need one of those anyway” and gave it to me. I was ecstatic! Between this post, this post, this post, this post, and this final project post you can tell that building a frequency counter was really important to me, and that I was never truly satisfied with the result – it wasn’t stable to the Hz! I’m excited to finally have a real counter at my workstation. (It’s an instek GFC-8010H, 1-120 MHz range.) Now onto figuring out how to build a spectrum analyzer… X_x
Update (2 days later)
I never can leave things alone can I? While basking in happiness over this new acquisition I pondered how easy it would be to interface this to a PC. I would like to graph frequency drift over time directly (not using a radio receiver outputting audio which I graph, since the radio is sensitive to drift). Plus this counter allows sample sizes of 10 seconds! That’s some serious resolution (compared to what I’m used to at least). First step to PC interfacing is to see what I’ve got to work with. I unscrewed the box and snapped some photos of the surprisingly simple device… I can’t believe this costs over $175 (as listed on Amazon.com) – it’s so simple!
I guess it all makes sense. AC transformer and rectifier diodes with a smoothing capacitor on the bottom left, fed into a 7805 linear voltage regulator, no doubt powering the micro-controller (big IC), logic buffer (small IC), and whatever analog circuitry is under the panel.
I’m not going to lift the panel because it’s obvious what’s under there. Likely some high gain, high distortion amplifier stages to provide a lot of buffering, eventually the input shape is fed to the chip for counting.
After posting and thinking about it, the curiosity got to me! I lifted the panel and this is what I found…
There’s our buffer and wave shaper! The full datasheet shows it’s a (triple) line driver.
Come to think of it, I’m not entirely sure about that smaller IC. It’s a 74HC00N, quad NAND gate. Knee-jerk was to say it was used for dividing-down the frequency, but that’s silly since it takes 2 NAND gates to make a flip flop, and that chip would be only 2 flip flops (/4), and there are flip flip chips for all that. Perhaps this has something to do with the buttons on the front panel? Perhaps something to do with square-shaping the oscillator with the 10mhz crystal? The big GFC 9701-1 IC seems to be a custom counter chip used in many Instek products. Here’s a blurb from a page of their manual for a function generator they make:
| The most important function of the internal counter is to show the main frequency on the display. So we take a square signal from the square shaper and change the level to TTL compatible level with a TTL shaper block (is this the role of that NAND gate?) then the signal will connect with the counter GFC-9701. Because the counter directly connects with the MPU system, the MPU can get correct frequency and show it on the display. |
So, it seems that chip is already outputting data ready to go into a CPU. I wonder if it’s outputting some type of data on an unused pin, ripe for the picking? I can’t find more ICs in this device, so it’s possible no other MCU is driving the display, and this counter IC is doing that all on its own. Bah, again curiosity is getting the best of me… [unscrews front panel]
More ICs! I couldn’t see them well before so I’m glad I opened up the display. The ULN2003A is a 7 channel darlington array, x2 = 14 darlingtons. The CD4511 is a common 7-segment driver – BINGO! If I’m going to interface this device by intercepting the display, this is the way to do it! The darlingtons tell me which character is selected, and the input of this chip tells me the value to be displayed. Pow!
Let’s take a closer look at that main chip again… X-RAY VISION TIME! I used Image-J to extract the red channel of the image and increased contrast, inverted, then used a 10 pixel wide unsharp mask with 0.8 weight to bring-out the leads. I guess I could have just unscrewed it and looked at the bottom, but where’s the fun in that? I imagine the top left pin is input of frequency. The bottom left pins go to buttons on the front, so they’re for front panel input. The headers on the right go to the front panel display. The pin going to the smaller IC must be the clock input, so that NAND gate DOES do something with shaping the input clock signal. On the top fight of the image you can see the crystal connecting to that gate. The trace going in the center of the chip on top is probably +5V supply for the chip. I’m not sure about much else, and I don’t feel like poking around with a continuity meter right now. UPDATE – I tested each pin with an analog o-scope. I found that pin 6 (unconnected) outputs a burst of data every time the display updates – this is my data line! If I had a logic analyzer I’d know how to read it… BAH!
What’s this?! The voltage regulator with its hefty heat sink (which obviously gets quite warm) is attached to a 10.000 MHz crystal! Is this the time base crystal? Doesn’t accuracy depend on thermostability of this crystal? It’s not just near it – it’s physically connected with it through metal! Does this imply that a loaded 7805 voltage regulator produces heat more steadily, and with a final temperature more stable than room air in a plastic enclosure??
update: The following was emailed to me in response to this puzzling issue. It’s from my good friend Bill!
| It may be an SC-cut crystal which is the best type for precision oscillators because the turn around inflection occurs at a much broader temperature range than the regular AT-cut, el cheapo types we often use. SC types, if carefully selected, can remain within a fraction of a ppm over a temperature range to 10 to 20 C. The turn around point temperature is pretty high, about 90 C, compared to around 25C for the at-cut. So, my guess is that the 7805 provides this really high temperature to the xtal and can be trusted to not vary by more than a few degrees, particularly in a laboratory environment. –Bill (W4HBK) |
Afterthought: This would make one hell of a huff-and-puff oscillator!
PROJECT COMPLETED!
I’m quite excited, the end product works wonderfully! It looks pretty spiffy too!
Here’s some video showing the device at work!
Of course Python and MatPlotLib can graph it:
… but so can Excel!
UPDATE Oops, I forgot to remove the trailing zero. That’s 9.9 MHz, not 99 MHz. That’s easy enough to do later, so I’m not going to fix it and re-post updated images. Don’t email me about it, I know ^_^
UPDATE 2 Here’s some useful data! I hooked up a canned oscillator at 3.57 something MHz (very stable) and watched it as my frequency counter warmed up. The result showed that the counter takes about 2 hours to warm up!!! he shift is only about 15 Hz over 2 hours, but still it’s good to know.
Once it’s warm, it’s stable!
Schematic
This device is very simple and specialized for my use and I have not designed a custom schematic. USB functionality is as recommended by V-USB, similar to:
For more information on the USB circuitry, view the hardware considerations page relating to the V-USB project.
CODE
Microcontroller code – Although it’s hard for me, I really don’t think I can release this right now. I’m working on an idiot’s guide to USB connectivity with ATMEL microcontrollers, and it would cause quite a stir to post that code too early. It’ll be shared soon! Here are the python scripts for the logging and for the graphing:
#This code polls the USB device and displays/logs frequency
from optparse import OptionParser
import time
import usb.core
import usb.util
import os
while True:
print "\nTrying to communicate with the Gator Keyer ...",
dev = usb.core.find(find_all=True, idVendor=0x16c0, idProduct=0x5dc)
if len(dev)==0: print "FAIL"
dev=dev[0]
dev.set_configuration()
print "there it is!"
break
def readVals(c):
x=dev.ctrl_transfer(0xC0, 3, c,4,4).tolist()
val=x[0]
if val>9: val=0
return val
def readDisp():
c=[]
for i in range(1,9):
val=readVals(i)
c.append(val)
#print "char",i,"=",val
disp="%d%d%d%d%d%d%d%d"%(c[0],c[1],c[2],c[5],c[6],c[3],c[4],c[7])
return disp
def readFreq():
i=0
first=readDisp()
while True:
if first==readDisp():
i+=1
if i==5: break #we're good!
else: #FAIL! start over...
i=0
first=readDisp()
return first
### PROGRAM START ##################
start=time.time()
while True:
line="%.02f,%s"%(time.time()-start,readFreq())
print line
f=open("freq.csv",'a')
f.write(line+"\n")
f.close()
time.sleep(1)
#This code reads the log file and graphs it with matplotlib
import matplotlib.pyplot as plt
import numpy
print "loading"
f=open("freq.csv")
raw=f.readlines()
f.close()
print raw
print "crunching"
times=numpy.array([])
data=numpy.array([])
for line in raw:
if len(line)<10: continue
line=line.replace("\n",'').split(',')
times=numpy.append(times,float(line[0]))
data=numpy.append(data,float(line[1]))
#data=data/1000000.0
print times, data
print "DONE processing",len(data),"lines\n\n"
print "plotting..."
plt.figure()
plt.grid()
plt.plot(times,data,'-')
plt.plot(times,data,'.')
plt.show()
» 4 Comments!
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