A few months ago I wrote about a way I use PHP to generate apache-style access.log files since my web host blocks access to them. Since then I’ve forgotten it was even running! I now have some pretty cool-looking graphs generated by Python and Matplotlib. For details (and the messy script) check the original posting.
This image represents the number of requests (php pages) made per hour since I implemented the script. It might be a good idea to perform some linear data smoothing techniques (which I love writing about), but for now I’ll leave it as it is so it most accurately reflects the actual data.
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I recently had the desire to be able to see data from an ATMEL AVR microcontroller (the ATTiny2313) for development and debugging purposes. I wanted an easy way to have my microcontroller talk to my PC (and vise versa) with a minimum number of parts. The easiest way to do this was to utilize the UART capabilities of the ATTiny2313 to talk to my PC through the serial port. One problem is that the ATTiny2313(as with most microcontrollers) puts out 5V for “high” (on) and 0V for “low” (off). The RS-232 standard (which PC serial ports use) required -15V for high and +15v for low! Obviously the microcontroller needs some help to achieve this. The easiest way was to use the MAX232 serial level converter which costs about 3 bucks at DigiKey. Note that it requires a few 10uF capacitors to function properly.
Here’s a more general schematic:
I connected my ATTiny2313 to the MAX232 in a very standard way. (photo) MAX232 pins 13 and 14 go to the serial port, and the ATTiny2313 pins 2 and 3 go to the MAX232 pins 12 and 11 respectively. I will note that they used a oscillator value (3.6864MHz) different than mine (9.216MHz).
Determining the speed of serial communication is important. This is dependent on your oscillator frequency! I said I used a 9.216Mhz oscillator. First, a crystal or ceramic oscillator is required over the internal RC oscillator because the internal RC oscillator is not accurate enough for serial communication. The oscillator you select should be a perfect multiple of 1.8432MHz. Mine is 5x this value. Many people use 2x this value (3.6864Mhz) and that’s okay! You just have to make sure your microchip knows (1) to use the external oscillator (google around for how to burn the fuses on your chip to do this) and (2) what the frequency of your oscillator is and how fast it should be sending data. This is done by setting the UBRRL value. The formula to do this is here:
The datasheet of your microcontroller may list a lot of common crystal frequencies, bandwidths, and their appropriate UBRR values. However my datasheet lacked an entry for a 9.216MHz crystal, so I had to do the math myself. I Googled around and no “table” is available! Why not make one? (picture, below). Anyway, for my case I determined that if I set the UBRR value to 239, I could transmit data at 2800 baud (bits/second). This is slow enough to ensure accuracy, but fast enough to quickly dump a large amount of text to a PC terminal.
This will make your life easier. The page wormfood.net/avrbaudcalc.php has a chart of common crystals and the baud rates they work best with! Try to pick a combination that provides the least error possible…
This is the bare-minimum code to test out my setup. Just load the code (written in C, compiled with avr-gcc) onto your chip and it’s ready to go. Be sure you set your fuses to use an external oscillator and that you set your UBRRL value correctly.
Once you load it, it’s ready to roll! It continuously dumps letters to the serial port. To receive them, open HyperTerminal (on windows, under accessories) or minicom (on Linux, look it up!). Set your baud rate to 2800 (or whatever you selected) and you’re in business. This (picture below) is the output of the microcontroller to HyperTerminal on my PC. Forgive the image quality, I photographed the LCD screen instead of taking a screenshot.
This is the circuit which generates the output of the previous image. I have a few extra components. I have an LED which I used for debugging purposes, and also a switch (labeled “R”). The switch (when pressed) grounds pin 1 of the ATTiny2313 which resets it. If I want to program the chip, I hold “R” down and the PC can program it with the inline programmer “parallel port, straight-through, DAPA style). One cable going into the circuit is for the parallel port programmer, one cable is for the serial port (data transfer), and one is for power (5v which I stole from a USB port).
I hope you found this information useful. Feel free to contact me with any questions you may have, but realize that I’m no expert, and I’m merely documenting my successes chronologically on this website.
I placed another online order to DigiKey yesterday. They have virtually every electronic component available for next-day delivery. How awesome is that? The frustrating thing is that I’m always trying to get my order in before 6pm CMT so that my package will ship same day, so I rush, and I always forget something! It never fails. 30 minutes after I place an order, I always remember something else I wish I’d added to the order (to save on shipping). So, instead of buying it when I want it (now) I wait a few more days to think of some more stuff to add. The last couple weeks I’ve placed 3 orders totaling about $30. You never think you’re spending a lot, but all the sudden you realize that all these 40-cent parts add up when you go to check out. Shipping is usually under $3, which makes me happy. What did I get? I got a couple MAX232 chips so I can easialy shuffle data back and forth from my PC to an AVR chip using the serial port using a simple terminal application like hyperterminal. This will allow me to do some pretty fancy stuff and certainly help with the prototyping/debugging/development steps of my various microcontroller-based projects.
A little random, but worth noting is a cool website I found earlier which details (in a very basic way) the various types of HF antennas and does a good job (IMHO) of explaining the basic theory behind them. The page can be found at deltadx.net.
Man, what a long day! Work is so tedious sometimes. This week I’ve been proofing scientific literature using Office 2003 with “track changes”. I make changes, my boss makes changes, I make more changes, and it goes back and forth a few times. I wonder why office 2007 is so bad. Does anybody truly like it, and find it to be a significant improvement upon 2003? … or Vista over XP? Maybe I’m just getting old, inflexible, and grumpy.
This is what I’m currently working on. The light bubbles on the right are deletions. The dark bubbles on the right are comments. The red text is insertions/modifications I made. Pretty intense, right? Pages and pages of this. I’m starting to grasp the daunting amount of time a scientist must spend writing in the laboratory as opposed to performing actual experiments or even doing literature research.
Last night I assembled a Pixie II circuit similar to the one pictured here. I must say that I’m a little disappointed with the information available on the internet regarding simple RF theory in relation to transceiver circuits. I’m just now starting to get into RF circuitry and the concept looking at circuits and imagining a combination of AC and DC flowing through it is warping my brain. I have everything I need to build a simple Pixie II transceiver (which is supposedly capable of Morse code transmissions over 300 miles, and QRSS applications over 3,000 miles) but I don’t want to use it unless I understand how it actually works.
I’m trying to break this circuit down into its primary components. I understand the role of the lowpass filter. I understand the role of the 1st transistor and related circuitry in amplifying the output of the crystal oscillator (left side). I totally get the audio amplifier circuitry (bottom). It’s that center transistor (which supposedly handles signal amplification, receiving, and mixing) that I can’t get my mind around. Every time I think figure it out for one mode (sending or receiving), I mentally lose the other one. It has me very frustrated because it seems like this should be easier than I’m making it. I selected this circuit because it was simple and I assumed I’d be smart enough to figure it out… maybe I was wrong? I wish I had an oscilloscope so I could probe the RF passing through various stages of this circuit. I guess I should take another stab at reading chapters 5-11 of the ARRL handbook.
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.
__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.
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’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!
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.
