## Prime Number Generator Rapid Prototype

In my quest to build a hardware-based binary prime number generator I decided to build a demonstration model / rapid prototype to prove to myself (and the world) that I can reliably (and quickly) generate prime numbers. This code needs a lot of work, but it’s functional. Instead of messing with tons of little LEDs, it just dumps the output to a LCD. Of note, the library to run the LCD takes up about 90% of the memory of the chip leaving only a handful of free bytes to write the actual code in!

Keep in mind this is a PROTOTYPE and that the full version will have over 80 LEDs to represent every number in binary form (up to 2^25, 33.5 million, with 25 LEDs/number). For now, this version (which dumps data to a HD44780 LCD screen) serves as a proof of concept. Powered by an ATTiny2313.

Here’s some video:

Here’s the code responsible:

```#define F_CPU 1E6
#include <stdlib.h>
#include <avr/io.h>
#include <math.h>
#include <util/delay.h>
#include "lcd.h"
#include "lcd.c"

const unsigned long int primeMax=pow(2,25);
unsigned long int primeLast=2;
unsigned long int primeTest=0;
unsigned int primeDivy=0;

void wait(void);
void init(void);
void updateDisplay(void);
char *toString(unsigned long int);

int main(void){
init();
short maybePrime;
unsigned int i;
//for(primeTest=3;primeTest<sqrt(primeMax);primeTest=primeTest+2){
for(primeTest=2;primeTest<sqrt(primeMax);primeTest++){
maybePrime=1;
//for (i=3;i<=(sqrt(primeTest)+1);i=i+2){
for (i=2;i<=(sqrt(primeTest)+1);i++){
primeDivy=i;
updateDisplay();
if (primeTest%primeDivy==0){maybePrime=0;break;}
}
if (maybePrime==1){primeLast=primeTest;updateDisplay();}
}
return 0;
}

void updateDisplay(void){
lcd_gotoxy(12,0);lcd_puts(toString(primeLast));
lcd_gotoxy(5,1);lcd_puts(toString(primeTest));
lcd_gotoxy(16,1);lcd_puts(toString(primeDivy));
//_delay_ms(1000);
return;
}

void init(void){
lcd_init(LCD_DISP_ON);
//lcd_clrscr();
lcd_puts("PRIME IDENTIFICATIONn");
//lcd_puts("MAX PRIME: ");
//lcd_puts(toString(primeMax));
//lcd_puts("nsquare root: ");
//lcd_puts(toString(sqrt(primeMax)+1));
_delay_ms(2000);
lcd_clrscr();
lcd_puts("LAST PRIME:n");
lcd_puts("TRY:");
lcd_gotoxy(14,1);lcd_puts("/");
return;
}

char *toString(unsigned long int x){
char s1[8];
ltoa(x,s1,10);
return s1;
}
```

In other news, I’ve seen the new Star Trek movie and found it enjoyable. My wife liked it too (perhaps more than I did). Here’s a relevant news story I found informative:

## Audio and Video on an ATMega88 Microcontroller!

At least 99% of my blog entries contain original content I created. However, I was so impressed by something I stumbled upon tonight that I absolutely cannot resist sharing it. It’s a project which aims to output audio and video simultaneously from a single microcontroller. The author’s site has all the details, but if you watch the video below you’ll be amazed. (Just get through the 30 second narration at the beginning) Apparently the guy rendered video in horizontal lines from the software and outputted audio signals between horizontal lines! Amazing!

On second thought, this was no big deal in the 80’s, so why am I so impressed by it now? The 8-bit microcontrollers this guy is programming is likely on par with the PCs of the 80’s. I guess that in the 70’s this would have been amazing because it was cutting edge. In the 80’s this would have been boring because it was commonplace. In the 2000’s, this is amazing because no one in my generation is old enough to remember how amazing this was in the 70’s and 80’s!

After researching some similar projects I realized I’m becoming fascinated with chiptune synthesizing code, hardware, and music. It’s basically a type of code to tell a synthesizer how to synthesize the music, rather than having it play pre-recorded music. It’s like a merge of a programming language and MIDI. For non-technical people, it’s like giving a microchip the sheet music for all the different instruments of an orchestra and having the microchip play everything from the sheet music, rather than giving it a CD to play. Here’s some video of a PC-based front-end to the audio creation process. Notice how each line represents a time, and how certain codes in certain channels represent notes (hence the MIDI aspect). Numbers on the far right represent the location of the memory, and notice also how it goes back and forth, replaying certain areas when necessary (to safe space, hence the coding aspect).

I can’t describe my emotional state right now. It’s like I have an extreme nostalgia for an era I never even lived in. This chip level audio synthesis stuff sounds amazingly fun to me. (I’ve already bookmarked nolife-radio.com and 8bitFM.com) I feel drawn toward it… but I’m scared to get sucked in.

I wish more than anything I were a college student in the 80’s studying electrical engineering. Here I am, having just gotten a master’s in molecular biology and microbiology, and I feel like I wasted six years of my life in the process. I’m about to start dental school in August. Hopefully when I look back from the future I won’t feel like I wasted another four years doing that.

Either way, I have an endless supply of possible projects to do this summer (not even going into the small list of projects I’m trying/expected to complete in the cardioneurophysiology lab I work in). I feel like I’m running out of time. I start dental school in August, and I dread the date. Not necessarily because I expect it to be difficult, but because I feel [however illogical, irrational, or ridiculous] that I’m actually doing something significant, working with my hands and working with my brain to do things that [almost] no one has done before, and doing things in a way that no one has ever thought of doing them. I feel like when I start resume classes, it’s another four years of people telling me how I should do things so I can be exactly like everyone else. How can you exercise creativity as a dental student? I’m sure there are ways, but it’s certainly leagues away from the projects engineering college students work on. As far as the career goes, if you’re an engineer the best case scenario is that you do something no one has ever done before. If you’re a dentist, the best case scenario is to do things exactly as everyone else does them. Maybe I’ll go crazy and change the wallpaper in my office every few months.

## ATTiny2313 Controlling a HD44780 LCD via AVR-GCC

After a day of tinkering I finally figured out how to control a HD44780-style LCD display from an ATTiny2313 class ATMEL AVR microcontroller. There are a lot of websites out there claiming to show you how to do this on similar AVRs. I tried about 10 of them and, intriguingly, only one of them worked! I don’t know if it’s user error, or an incompatibility of the ATTiny2313 running code written for an ATMega8, but since it took me so long to get this right I decided to share it on the internet for anyone else having a similar struggle. First, the results:

You might recognize this LCD panel from some PC parallel port / LCD interface projects I worked on about 5 years ago. It’s a 20-column, 2-row, 8-bit parallel character LCD. This means that ranter than telling each little square to light up to form individual letters, you can just output text to the microcontroller embedded in the display and it can draw the letters, move the cursor, or clear the screen.

As you can see this thing is pretty easy to wire-up to the ATTiny2313. These are the connections I made:

• LCD1 -> GND
• LCD2 -> +5V
• LCD3 (contrast) -> GND
• LCD4 (RS) -> AVR D0 (pin2)
• LCD5 (R/W) -> AVR D1 (pin3)
• LCD6 (ES) -> AVR D2 (pin6)
• LCD 11-14 (data) -> AVR B0-B3 (pins 12-15)

The code I used to FINALLY allow me to control this LCD from the ATTiny2313 was found on Martin Thomas’ page. [HIS CODE] I included the .h and .c files and successfully ran the following program (with great results) on my AVR. The internal RC clock works, and supposedly any external clock (<8MHz) should work too.

```// THIS THE TEST PROGRAM "main.c"
// ATTiny2313 / HD44780 LCD INTERFACE
#include <stdlib.h>
#include <avr/io.h>
#include <util/delay.h>
#include "lcd.h"
#include "lcd.c"

int main(void)
{
int i=0;
lcd_init(LCD_DISP_ON);
lcd_clrscr();
lcd_puts("ATTiny 2313 LCD Demo");
lcd_puts("  www.SWHarden.com  ");
_delay_ms(1000);
lcd_clrscr();
for (;;) {
lcd_putc(i);
i++;
_delay_ms(50);
}
}
```
```// THIS IS PART OF MY INCLUDED "lcd.h"
// THE WIRING CHART DESCRIBED IN THIS BLOG ENTRY
// IS MATCHED TO THE VALUES DISPLAYED BELOW
#define LCD_PORT         PORTB        /**< port for the LCD lines   */
#define LCD_DATA0_PORT   LCD_PORT     /**< port for 4bit data bit 0 */
#define LCD_DATA1_PORT   LCD_PORT     /**< port for 4bit data bit 1 */
#define LCD_DATA2_PORT   LCD_PORT     /**< port for 4bit data bit 2 */
#define LCD_DATA3_PORT   LCD_PORT     /**< port for 4bit data bit 3 */
#define LCD_DATA0_PIN    0            /**< pin for 4bit data bit 0  */
#define LCD_DATA1_PIN    1            /**< pin for 4bit data bit 1  */
#define LCD_DATA2_PIN    2            /**< pin for 4bit data bit 2  */
#define LCD_DATA3_PIN    3            /**< pin for 4bit data bit 3  */
#define LCD_RS_PORT      PORTD     /**< port for RS line         */
#define LCD_RS_PIN       0            /**< pin  for RS line         */
#define LCD_RW_PORT      PORTD     /**< port for RW line         */
#define LCD_RW_PIN       1            /**< pin  for RW line         */
#define LCD_E_PORT       PORTD     /**< port for Enable line     */
#define LCD_E_PIN        2            /**< pin  for Enable line     */

// AND A LITTLE LOWER, I CHANGED THIS LINE TO 4-BIT MODE
#define LCD_FUNCTION_8BIT     0      /*   DB4: set 8BIT mode (0->4BIT mode) */
```

And some video of the output… Notice how this display can show English (lowercase/uppercase/numbers) as well as the Japanese character set! Sweet!

## Simple Case AVR/PC Serial Communication via MAX232

### UPDATE: I found a method of PC/microcontroller communication which I feel is simpler, easier, and definitely cheaper than this! It’s not good for everything, but worth looking at. It’s a way to communicate with a PC using your sound card and zero components!

Another page HERE has more info on how to do this with an intermediate IC if yours doesn’t have RX/TX pins…

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.

## >>> IMPORTANT UPDATE!

`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.

```

#include <avr/io.h>

#include <avr/interrupt.h>

#include <util/delay.h>

int main (void)

{

unsigned char data=0;

UBRRL = 239;

UCSRB = (1 < < RXEN) | (1 << TXEN);

UCSRC = (1 < < UCSZ1) | (1 << UCSZ0);

for (;;)

{

if (data>'Z'||data< 'A')

{

UDR = 10; UDR = 13; data='A';_delay_ms(100);

}

UDR = data;

data += 1;

_delay_ms(100);

}

}

```

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.

## Barebones AM Transmitter Test

Okay, so I put the bare bones transmitter in the previous entry to the test. Before I go any farther, let’s hit the legal. DO NOT ATTEMPT THIS. I DID NOT DO THIS. THIS IS HYPOTHETICAL ONLY. ATTEMPTING ANYTHING SIMILAR TO WHAT IS ABOUT TO BE DESCRIBED MAY BE ILLEGAL IN YOUR COUNTRY. DO NOT ATTEMPT! THE DESCRIBED CIRCUITRY HAS NO OUTPUT FILTERING AND MAY SERVE AS AN EFFECTIVE RADIO JAMMER. EAT FRUITS AND VEGGIES DAILY. Anyway, I changed the circuitry a bit though. I kept the oscillator (50.0000MHz) continuously powered and programmed the ATTiny 2313 microcontroller (using PWM output) to oscillate (high/low) 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, effectively removing power from it. In retrospect, I should have added a resistor between the oscillator and the transistor so that it didn’t completely ground it, because I think the oscillator would have functioned better if it were not fully grounded. Anyway, 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. With this bare bones transmitter setup (using my ungrounded 2m jpole antenna NOT TUNED for the transmitter frequency) I was able to detect it over 4000 ft away. The receiving antenna was a 2m ~1ft high antenna magmounted on top of my car. In retrospect, I should have built a decent antenna and kept ARGO running 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 n00b. I’m learning. That’s the point though right?

Here’s the signal (on my laptop) as I drove away…

This is where I was when the signal died. The red dot is my apartment (transmitter location), 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.

## A Foot in the QRSS Door

I’ve been unbelievably 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 5pm). Scientific research grants are not easy to prepare. ~40 pages of forms to fill out, biographies to design for each of the lab workers, budget appropriation plans, animal handling protocol approval forms, plus 12 pages of scientific dialogue explaining the experiment. Now, I know that it may not sound like much, but trust me – it’s a very dense (11 and 9pt Arial font, single spaced) paper which takes about 2.5 hours for me to read from start to finish. Being the only native English speaker in the laboratory, I’m expected to assist in the polishing of its dialogue, as well as thoroughly evaluate its scientific content and offer suggestions. 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 4pm) I went home and collapsed in 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 at all. Anyway, in exchange for my over-weekend work I got Tuesday and Wednesday off.

So, what did you do on your mid-week weekend? Well, I knew in advance that I’d have two days to bask in freedom and 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. I know I could have gotten better deals elsewhere “Like \$1.88 per chip from RoboticsWorld) but the truth is that I had a random assortment of items I wanted to buy, and although all these different companies offered them, I feel I saved in the long run by ordering everything from a single source, cutting down on shipping costs. I also was impressed by the delivery time! I got my boxes in the mail on Monday. Way better (and cheaper) than ordering from the UK or Hong Kong.

The first thing I did with these chips was try to program them. Unlike the embarrassingly-easy 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 equivalent ASM (thanks to AVR-GCC) and loaded onto these chips. The result is a much faster and more powerful coding platform than the PICAXE chips. PICAXE chips are great for rapid development or for a starting platform for microcontroller education, but I feel that I’m ready to tackle something new. Anyway, I built a straight-through parallel programmer for my ATTiny2313 chips. It was based upon the dapa configuration and connects to the appropriate pins of the ATTiny 2313. However I would recommend that you be safe (protect your parallel port and microcontrollers) by installing the proper resisters (~1k?) between the devices, but I didn’t do this. No no. I live on the wild side. I eat danger for breakfast.

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 be able to control the power level given to a 3.579545 MHz oscillator. Check out the circuit. 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 (uber-old) scanner at its 9th harmonic (32.215905 MHz). Supposedly 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 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.

## Unlimited Freedom: Day 1

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

Here’s that internal photo I promised I’d get posted yesterday…

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

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

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

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

I wanted to toss this picture out there. I’ve slightly improved the connection between my radio’s coax cable to the ghettorigged jpole antenna I made.

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

I just realized I didn’t post an image of the inside (complex wiring) of the device. Maybe later.