The personal website of Scott W Harden
August 26th, 2010

# Minimalist Crystal Oven

So I'm working on building a crystal oven to keep my QRSS MEPT (radio transmitter) at an extremely stable frequency. Even inside a thick Styrofoam box, slight changes in my apartment temperature caused by the AC turning on and off is enough to change the crystal temperature of the transmitter, slightly modifying its oscillation frequency. For a device that vibrates exactly 10,140,070 times a second, even 3 to many or too few vibrations per second is too much. Keeping in the spirit of hacking things together with a minimum of parts, this is what I came up with!

It uses a thermistor, potentiometer, and comparator of a microcontroller (ATTiny44a) to tightly sense and regulate temperature. The heater element is a junk MOSFET I found in an old battery backup system. I simply have pass a ton of current (turned on/off by the gate) to generate heat, transferred into a piece of steel for smooth regulation. One of the unexpected advantages is that the light flickers rapidly near equilibrium, which is great because it has the ability to turn the heater on a little or a lot based upon the averaging effect of the flicker. Here is the code I wrote on the microcontroller to handle the comparator. It couldn't be simpler!

#include <avr/io.h>
#include <util/delay.h>

int main(void)
{
DDRA = 0;   // all inputs
DDRB = 255; // all outputs

while (1)
{
if (ACSR & _BV(ACO))
{
/* AIN0 is more positive than AIN1 right now */
PORTB |= (1 << PB0);
PORTB &= ~(1 << PB1);
}
else
{
/* AIN0 is more negative than AIN1 */
PORTB |= (1 << PB1);
PORTB &= ~(1 << PB0);
}
}
}
---
title: Minimalist Crystal Oven
date: 2010-08-26 10:40:16
---

# Minimalist Crystal Oven

__So I'm working on building a crystal oven__ to keep my QRSS MEPT (radio transmitter) at an extremely stable frequency. Even inside a thick Styrofoam box, slight changes in my apartment temperature caused by the AC turning on and off is enough to change the crystal temperature of the transmitter, slightly modifying its oscillation frequency. For a device that vibrates exactly 10,140,070 times a second, even 3 to many or too few vibrations per second is too much. Keeping in the spirit of hacking things together with a minimum of parts, this is what I came up with!

__It uses a thermistor, potentiometer, and comparator of a microcontroller (ATTiny44a)__ to tightly sense and regulate temperature. The heater element is a junk MOSFET I found in an old battery backup system. I simply have pass a ton of current (turned on/off by the gate) to generate heat, transferred into a piece of steel for smooth regulation. One of the unexpected advantages is that the light flickers rapidly near equilibrium, which is great because it has the ability to turn the heater on a little or a lot based upon the averaging effect of the flicker. Here is the code I wrote on the microcontroller to handle the comparator. It couldn't be simpler!

```c
#include <avr/io.h>
#include <util/delay.h>

int main(void)
{
DDRA = 0;   // all inputs
DDRB = 255; // all outputs

while (1)
{
if (ACSR & _BV(ACO))
{
/* AIN0 is more positive than AIN1 right now */
PORTB |= (1 << PB0);
PORTB &= ~(1 << PB1);
}
else
{
/* AIN0 is more negative than AIN1 */
PORTB |= (1 << PB1);
PORTB &= ~(1 << PB0);
}
}
}
```

June 6th, 2010

I'm still working on this project, and although progress is slow I'm learning a lot and the circuit is getting better with time. I'm still not yet ready to post the schematics, but you can get an idea of what's going on from the picture. It can handle 255 levels of frequency shift and has the ability to turn the tone on and off. 6 capacitors, 3 resistors, 4 transistors, a single inductor, and a micro-controller.

UPDATE I spotted myself on W4BHK's Grabber about 300 miles away...

#include <avr /io.h>
#include <util /delay.h>

char dotlen = 5;                              // ultimately the speeed of transmission
char call[] = {0, 1, 1, 1, 2, 0, 2, 1, 1, 0}; // 0 for space, 1 for dit, 2 for dah

void setfor(char freq, char ticks)
{
OCR1A = freq;
while (ticks > 0)
{
sleep();
ticks--;
}
}

void sleep()
{
for (char i = 0; i < dotlen; i++)
{
_delay_loop_2(65000);
}
}

void slideto(char freq, char ticks)
{
freq = freq + 30;
char step = 1;
if (OCR1A > freq)
{
step = -1;
}
while (OCR1A != freq)
{
OCR1A += step;
setfor(OCR1A, 1);
}
setfor(freq, ticks);
}

void DNA()
{
char a[] = {4, 5, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 7, 7, 7, 7, 6, 6, 6, 5, 5, 4, 3, 3, 2, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 3, 3};
char b[] = {1, 1, 1, 1, 2, 2, 2, 3, 3, 4, 5, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 7, 7, 7, 7, 6, 6, 6, 5, 5, 4, 3, 3, 2, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0};
for (char i = 0; i < sizeof(a); i++)
{
//slideto(a[i]*4,2);
//slideto(b[i]*4,2);
setfor(a[i] * 2 + 5, 10);
setfor(b[i] * 2 + 5, 10);
}
}

void ID()
{
for (char i = 0; i < sizeof(call); i++)
{
setfor(10, 50);
if (call[i] == 0)
{
setfor(10, 100);
}
if (call[i] == 1)
{
setfor(15, 100);
}
if (call[i] == 2)
{
setfor(15, 250);
}
setfor(10, 50);
}
}

void ID2()
{
for (char i = 0; i < sizeof(call); i++)
{
if (call[i] == 0)
{
ampOFF();
setfor(10, 50);
}
if (call[i] == 1)
{
ampON();
setfor(10, 100);
}
if (call[i] == 2)
{
ampON();
setfor(13, 100);
}
ampOFF();
setfor(OCR1A, 30);
}
ampON();
}

void ampON()
{
PORTA |= (1 << PA7);
PORTA |= (1 << PA0);
PORTA &= ~(1 << PA1);
_delay_loop_2(10000);
}
void ampOFF()
{
PORTA &= ~(1 << PA7);
PORTA |= (1 << PA1);
PORTA &= ~(1 << PA0);
_delay_loop_2(10000);
}

int main(void)
{
DDRA = 255;
OCR1A = 75;
TCCR1A = 0x81;
TCCR1B = 1;
while (1)
{
ID2();
ID();
for (char i = 0; i < 3; i++)
{
DNA();
}
}
}
---
date: 2010-06-06 19:15:58
---

__I'm still working on this project,__ and although progress is slow I'm learning a lot and the circuit is getting better with time. I'm still not yet ready to post the schematics, but you can get an idea of what's going on from the picture. It can handle 255 levels of frequency shift and has the ability to turn the tone on and off. 6 capacitors, 3 resistors, 4 transistors, a single inductor, and a micro-controller.

<div class="text-center img-border">

[![](DSCN0776_thumb.jpg)](DSCN0776.jpg)
[![](OnOffDNA_thumb.jpg)](OnOffDNA.png)
[![](dnareport_thumb.jpg)](dnareport.jpg)

</div>

__UPDATE__ I spotted myself on [W4BHK's Grabber](http://www.qsl.net/w4hbk/W4HBKgrabber.html) about 300 miles away...

```c
#include <avr /io.h>
#include <util /delay.h>

char dotlen = 5;                              // ultimately the speeed of transmission
char call[] = {0, 1, 1, 1, 2, 0, 2, 1, 1, 0}; // 0 for space, 1 for dit, 2 for dah

void setfor(char freq, char ticks)
{
OCR1A = freq;
while (ticks > 0)
{
sleep();
ticks--;
}
}

void sleep()
{
for (char i = 0; i < dotlen; i++)
{
_delay_loop_2(65000);
}
}

void slideto(char freq, char ticks)
{
freq = freq + 30;
char step = 1;
if (OCR1A > freq)
{
step = -1;
}
while (OCR1A != freq)
{
OCR1A += step;
setfor(OCR1A, 1);
}
setfor(freq, ticks);
}

void DNA()
{
char a[] = {4, 5, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 7, 7, 7, 7, 6, 6, 6, 5, 5, 4, 3, 3, 2, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 3, 3};
char b[] = {1, 1, 1, 1, 2, 2, 2, 3, 3, 4, 5, 5, 6, 6, 6, 7, 7, 7, 7, 8, 8, 8, 8, 8, 7, 7, 7, 7, 6, 6, 6, 5, 5, 4, 3, 3, 2, 2, 2, 1, 1, 1, 1, 0, 0, 0, 0, 0};
for (char i = 0; i < sizeof(a); i++)
{
//slideto(a[i]*4,2);
//slideto(b[i]*4,2);
setfor(a[i] * 2 + 5, 10);
setfor(b[i] * 2 + 5, 10);
}
}

void ID()
{
for (char i = 0; i < sizeof(call); i++)
{
setfor(10, 50);
if (call[i] == 0)
{
setfor(10, 100);
}
if (call[i] == 1)
{
setfor(15, 100);
}
if (call[i] == 2)
{
setfor(15, 250);
}
setfor(10, 50);
}
}

void ID2()
{
for (char i = 0; i < sizeof(call); i++)
{
if (call[i] == 0)
{
ampOFF();
setfor(10, 50);
}
if (call[i] == 1)
{
ampON();
setfor(10, 100);
}
if (call[i] == 2)
{
ampON();
setfor(13, 100);
}
ampOFF();
setfor(OCR1A, 30);
}
ampON();
}

void ampON()
{
PORTA |= (1 << PA7);
PORTA |= (1 << PA0);
PORTA &= ~(1 << PA1);
_delay_loop_2(10000);
}
void ampOFF()
{
PORTA &= ~(1 << PA7);
PORTA |= (1 << PA1);
PORTA &= ~(1 << PA0);
_delay_loop_2(10000);
}

int main(void)
{
DDRA = 255;
OCR1A = 75;
TCCR1A = 0x81;
TCCR1B = 1;
while (1)
{
ID2();
ID();
for (char i = 0; i < 3; i++)
{
DNA();
}
}
}
```

July 6th, 2009

# Microcontroller-Powered Prime Number Generator

My microcontroller-powered prime number calculator is complete! Although I'm planning on improving the software (better menus, the addition of sound, and implementation of a more efficient algorithm) and hardware (a better enclosure would be nice, battery/DC wall power, and a few LEDs on the bottom row are incorrectly wired), this device is currently functional therefore I met my goal!

This device generates large prime numbers (v) while keeping track of how many prime numbers have been identified (N). For example, the 5th prime number is 11. Therefore, at one time this device displayed N=5 and V=11. N and V are displayed on the LCD. In the photo the numbers mean the 16,521,486th prime is 305,257,039 (see for yourself!). The LCD had some history. In December, 2003 (6 years ago) I worked with this SAME display, and I even located the blog entry on November 25'th, 2003 where I mentioned I was thinking of buying the LCD (it was \$19 at the time). Funny stuff. Okay, fast forward to today. Primes (Ns and Vs) are displayed on the LCD.

In addition to the LCD, numbers are displayed in binary: Each row of LEDs represents a number. Each row of 30 LEDs allows me to represent numbers up to 2^31-1 (2,147,483,647, about 2.15 billion) in the binary numeral system. Since there's no algorithm to simply generate prime numbers (especially the Nth prime), the only way to generate large Nth primes is to start small (2) and work up (to 2 billion) testing every number along the way for primeness. The number being tested is displayed on the middle row (Ntest). The last two digits of Ntest are shown on the top left. To test a number (Ntest) for primeness, it is divided by every number from 2 to the square root of Ntest. If any divisor divides evenly (with a remainder of zero) it's assumed not to be prime, and Ntest is incremented. If it can't be evenly divided by any number, it's assumed to be prime and loaded into the top row. In the photo (with the last prime found over 305 million) the device is generating new primes every ~10 seconds.

I'd like to emphasize that this device is not so much technologically innovative as it is creative in its oddness and uniqueness. I made it because no one's ever made one before. It's not realistic, practical, or particularly useful. It's just unique. The brain behind it is an ATMEL ATMega8 AVR microcontroller (What is a microcontroller?), the big 28-pin microchip near the center of the board. (Note: I usually work with ATTiny2313 chips, but for this project I went with the ATMega8 in case I wanted to do analog-to-digital conversions. The fact that the ATMega8 is the heart of the Arduino is coincidental, as I'm not a fan of Arduino for purposes I won't go into here).

_I'd like to thank my grandmother's brother and his wife (my great uncle and aunt I guess) for getting me interested in microcontrollers almost 10 years ago when they gave me BASIC Stamp kit (similar to this one) for Christmas. I didn't fully understand it or grasp its significance at the time, but every few years I broke it out and started working with it, until a few months ago when my working knowledge of circuitry let me plunge way into it. I quickly outgrew it and ventured into directly programming cheaper microcontrollers which were nearly disposable (at \$2 a pop, compared to \$70 for a BASIC stamp), but that stamp kit was instrumental in my transition from computer programming to microchip programming._

The microcontroller is currently running at 1 MHz, but can be clocked to run faster. The PC I'm writing this entry on is about 2,100 MHz (2.1 GHz) to put it in perspective. This microchip is on par with computers of the 70s that filled up entire rooms. I program it with the C language (a language designed in the 70s with those room-sized computers in mind, perfectly suited for these microchips) and load software onto it through the labeled wires two pictures up. The microcontroller uses my software to bit-bang data through a slew of daisy-chained shift registers (74hc595s, most of the 16-pin microchips), allowing me to control over 100 pin states (on/off) using only 3 pins of the microcontroller. There are also 2 4511-type CMOS chips which convert data from 4 pins (a binary number) into the appropriate signals to illuminate a 7-segment display. Add in a couple switches, buttons, and a speaker, and you're ready to go!

I'll post more pictures, videos, and the code behind this device when it's a little more polished. For now it's technically complete and functional, and I'm very pleased. I worked on it a little bit every day after work. From its conception on May 27th to completion July 5th (under a month and a half) I learned a heck of a lot, challenged my fine motor skills to complete an impressive and confusing soldering job, and had a lot of fun in the process.

---
title: Microcontroller-Powered Prime Number Generator
date: 2009-07-06 10:07:56
tags: microcontroller
---

# Microcontroller-Powered Prime Number Generator

__My microcontroller-powered prime number calculator is complete!__ Although I'm planning on improving the software (better menus, the addition of sound, and implementation of a more efficient algorithm) and hardware (a better enclosure would be nice, battery/DC wall power, and a few LEDs on the bottom row are incorrectly wired), this device is currently functional therefore I met my goal!

<div class="text-center img-border">

[![](primepic1_thumb.jpg)](primepic1.jpg)

</div>

__This device generates large prime numbers (v) while keeping track of how many prime numbers have been identified (N).__ For example, the 5th prime number is 11. Therefore, at one time this device displayed N=5 and V=11. N and V are displayed on the LCD. In the photo the numbers mean the 16,521,486th prime is 305,257,039 ([see for yourself!](http://primes.utm.edu/nthprime/index.php#nth)). The LCD had some history. [In December, 2003 (6 years ago) I worked with this SAME display](http://www.swharden.com/blog/2003/12/), and I even located the [blog entry on November 25'th, 2003](http://www.swharden.com/blog/2003-11-25-doh/) where I mentioned I was thinking of buying the LCD (it was \$19 at the time). Funny stuff. Okay, fast forward to today. Primes (Ns and Vs) are displayed on the LCD.

<div class="text-center img-border">

[![](primepic2_thumb.jpg)](primepic2.jpg)

</div>

__In addition to the LCD, numbers are displayed in binary:__ __Each row of LEDs represents a number. __Each row of 30 LEDs allows me to represent numbers up to 2^31-1 (2,147,483,647, about 2.15 billion) in [the binary numeral system](http://en.wikipedia.org/wiki/Binary_numeral_system). Since there's no algorithm to simply generate prime numbers (especially the Nth prime), the only way to generate large Nth primes is to start small (2) and work up (to 2 billion) testing every number along the way for primeness. The number being tested is displayed on the middle row (N_test_). The last two digits of N_test_ are shown on the top left. To test a number (N_test_) for primeness, it is divided by every number from 2 to the square root of N_test_. If any divisor divides evenly (with a remainder of zero) it's assumed not to be prime, and N_test_ is incremented. If it can't be evenly divided by any number, it's assumed to be prime and loaded into the top row. In the photo (with the last prime found over 305 million) the device is generating new primes every ~10 seconds.

__I'd like to emphasize that__ this device is not so much technologically innovative as it is creative in its oddness and uniqueness. I made it because no one's ever made one before. It's not realistic, practical, or particularly useful. It's just unique. The brain behind it is an [ATMEL ATMega8 AVR microcontroller](http://thinklabs.in/shop/images/mega8.jpg) (_[What is a microcontroller?](http://en.wikipedia.org/wiki/Microcontroller)_), the big 28-pin microchip near the center of the board. (Note: I usually work with ATTiny2313 chips, but for this project I went with the ATMega8 in case I wanted to do analog-to-digital conversions. The fact that the ATMega8 is the heart of the [Arduino](http://en.wikipedia.org/wiki/Arduino) is coincidental, as I'm not a fan of Arduino for purposes I won't go into here).

___I'd like to thank my grandmother's brother and his wife (my great uncle and aunt I guess)__ for getting me interested in microcontrollers almost 10 years ago when they gave me BASIC Stamp kit ([similar to this one](http://www.colinfahey.com/ps2_mouse_and_basic_stamp_computer/2002june03_basicstamp_mousecircuit01_adj.jpg)) for Christmas. I didn't fully understand it or grasp its significance at the time, but every few years I broke it out and started working with it, until a few months ago when my working knowledge of circuitry let me plunge way into it. I quickly outgrew it and ventured into directly programming cheaper microcontrollers which were nearly disposable (at \$2 a pop, compared to \$70 for a BASIC stamp), but that stamp kit was instrumental in my transition from computer programming to microchip programming._

__The microcontroller is currently running at 1 MHz__, but can be clocked to run faster. The PC I'm writing this entry on is about 2,100 MHz (2.1 GHz) to put it in perspective. This microchip is on par with computers of the 70s that filled up entire rooms. I program it with [the C language](http://en.wikipedia.org/wiki/C_(programming_language)) (a language designed in the 70s with those room-sized computers in mind, perfectly suited for these microchips) and load software onto it through the labeled wires two pictures up. The microcontroller uses my software to [bit-bang](http://en.wikipedia.org/wiki/Bit-banging) data through a slew of daisy-chained [shift registers](http://en.wikipedia.org/wiki/Shift_register) (74hc595s, most of the 16-pin microchips), allowing me to control over 100 pin states (on/off) using only 3 pins of the microcontroller. There are also 2 4511-type CMOS chips which convert data from 4 pins (a binary number) into the appropriate signals to illuminate a 7-segment display. Add in a couple switches, buttons, and a speaker, and you're ready to go!

__I'll post more__ pictures, videos, and the code behind this device when it's a little more polished. For now it's technically complete and functional, and I'm very pleased. I worked on it a little bit every day after work. From its conception on May 27th to completion July 5th (under a month and a half) I learned a heck of a lot, challenged my fine motor skills to complete an impressive and confusing soldering job, and had a lot of fun in the process.

<div class="text-center img-border">

[![](primepic3_thumb.jpg)](primepic3.jpg)

</div>
July 1st, 2009

# Summer's End is Nearing

My favorite summer yet is reaching its end. With about a month and a half before I begin dental school, I pause to reflect on what I've done, and what I still plan to do. Unlike previous summers where my time was devoted to academic requirements, this summer involved a 9-5 job with time to do whatever I wanted after. I made great progress in the realm of microcontroller programming, and am nearing the completion of my prime number calculator. I'm very happy with its progress.

Most of the LEDs are working but I'm still missing a few shift registers. It's not that they're missing, so much as I broke them. (D'oh!) I have to wait for a dozen more to come in the mail so I can continue this project. Shift registers are also responsible for powering the binary-to-7-segment chips on the upper left, whose sockets are currently empty.

Since this project is on pause, I began work hacking a VFD I heard about at Skycraft. It's a 20x2 character display (forgot to photograph the front) and if I can make it light up, it will be gorgeous.

Here's a high resolution photo of the back panel of the VFD. I believe it used to belong to an old cash register, and it has some digital interfacing circuitry between the driver chips (the big OKI ones) and the 9-pin input connector. I think my best bet for being able to control this guy as much as I want is to attack those driver chips, with help from the Oki C1162A datasheet. It looks fairly straightforward. As long as I don't screw up my surface-mount soldering, and assuming that I come up with 65 volts to power the thing (!) I think it's a doable project.

---
title: Summer's End is Nearing
date: 2009-07-01 09:40:43
tags: microcontroller
---

# Summer's End is Nearing

<div class="text-center img-border">

[![](scott_working_thumb.jpg)](scott_working.png)

</div>

__My favorite summer yet is reaching its end.__ With about a month and a half before I begin dental school, I pause to reflect on what I've done, and what I still plan to do. Unlike previous summers where my time was devoted to academic requirements, this summer involved a 9-5 job with time to do whatever I wanted after. I made great progress in the realm of microcontroller programming, and am nearing the completion of my prime number calculator. I'm very happy with its progress.

<div class="text-center img-border">

[![](wiremess_thumb.jpg)](wiremess.jpg)
[![](lightson_thumb.jpg)](lightson.jpg)

</div>

__Most of the LEDs are working__ but I'm still missing a few shift registers. It's not that they're missing, so much as I broke them. (D'oh!) I have to wait for a dozen more to come in the mail so I can continue this project. Shift registers are also responsible for powering the binary-to-7-segment chips on the upper left, whose sockets are currently empty.

Since this project is on pause, I began work hacking a [VFD](http://en.wikipedia.org/wiki/Vacuum_fluorescent_display) I heard about at Skycraft. It's a 20x2 character display (forgot to photograph the front) and if I can make it light up, it will be gorgeous.

<div class="text-center">

[![](vfd_thumb.jpg)](vfd.jpg)

</div>

__Here's a high resolution photo of the back panel of the VFD__. I believe it used to belong to an old cash register, and it has some digital interfacing circuitry between the driver chips (the big OKI ones) and the 9-pin input connector. I think my best bet for being able to control this guy as much as I want is to attack those driver chips, with help from the Oki C1162A datasheet. It looks fairly straightforward. As long as I don't screw up my surface-mount soldering, and assuming that I come up with 65 volts to power the thing (!) I think it's a doable project.

June 4th, 2009

# Prime Prototype Construction

Now that I've worked-out the software side of the microcontroller-powered prime number generator, it's time to start working on the hardware. I want to make a prototype which is far smaller and simpler than the final version but lets me practice driving lots of LEDs (30). I expect the final version to have around 80. Also, the heart of this project is an ATTiny2313 microcontroller, and for the full version I'd like to use an ATMEega8. I picked up an unfinished wooden box with a magnetic latch from Michaels. It's delicate and tends to chip when you drill it, but moving slowly I'm able to make nice evenly-spaced holes.

This is the circuit concept. The chip is an ATTiny2313, sourced with 5V, where the left pins control the columns (by providing current) and the right pins control the rows (by providing ground). The "holes" at the top of the circuit represent where I hook up my PC and external power for testing purposes.

Thoughts from Future Scott (10 years later, August, 2019)

A+ for enthusiasm and construction but your design is... just no!

Why are you using an external crystal?

The schematic for the crystal is wrong: those capacitors should be to ground not in series!

You made the circuit diagram in InkScape!

You shouldn't drive current directly out of the microcontroller pins.

The majority of the microcontroller CPU cycles will go into managing multiplexing of the display (not calculating primes).

After a little more work I have a functional device and it looks better than I expected. There are a few more features I want to add, and I want to work on the code some more, but I hope to be done tomorrow. The coolest part is that I've included an internal button which drives a pause/resume and speed-controller menu based upon the length of button presses! There's a lot of awesome stuff I want to write, but once again, I'll save it for the completed project page.

I rendered the cover sticker wrong and all the LEDs are mislabled. The first LED should be 2^0 (1), and the second should be 2^1 (2), etc. Also, 2^22 and 2^23 are mislabeled - oops! But the thing really does generate, differentiate, and display [only[ prime numbers. Once again, videos (including demonstration of the menus and the programming options) and source code will be posted soon.

---
title: Prime Prototype Construction
date: 2009-06-04 12:46:18
tags: circuit, microcontroller
---

# Prime Prototype Construction

__Now that I've worked-out the software side of the microcontroller-powered prime number generator, it's time to start working on the hardware.__ I want to make a prototype which is far smaller and simpler than the final version but lets me practice driving lots of LEDs (30). I expect the final version to have around 80. Also, the heart of this project is an ATTiny2313 microcontroller, and for the full version I'd like to use an ATMEega8. I picked up an unfinished wooden box with a magnetic latch from Michaels. It's delicate and tends to chip when you drill it, but moving slowly I'm able to make nice evenly-spaced holes.

<div class="img-border img-micro">

[![](img_2028_thumb.jpg)](img_2028.jpg)
[![](img_2041_thumb.jpg)](img_2041.jpg)
[![](img_2043_thumb.jpg)](img_2043.jpg)
[![](img_2047_thumb.jpg)](img_2047.jpg)
[![](img_2054_thumb.jpg)](img_2054.jpg)
[![](img_2056_thumb.jpg)](img_2056.jpg)
[![](img_2057_thumb.jpg)](img_2057.jpg)
[![](img_2058_thumb.jpg)](img_2058.jpg)
[![](img_2062_thumb.jpg)](img_2062.jpg)
[![](img_2025_thumb.jpg)](img_2025.jpg)

</div>

__This is the circuit concept. __The chip is an ATTiny2313, sourced with 5V, where the left pins control the columns (by providing current) and the right pins control the rows (by providing ground). The "holes" at the top of the circuit represent where I hook up my PC and external power for testing purposes.

<div class="text-center">

[![](prime-number-broken-circuit_thumb.jpg)](prime-number-broken-circuit.png)

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<blockquote class="wp-block-quote"><p><strong>Thoughts from Future Scott (10 years later, August, 2019)</strong></p><p>A+ for enthusiasm and construction but your design is... just no!</p><p>Why are you using an external crystal? </p><p>The schematic for the crystal is wrong: those capacitors should be to ground not in series!</p><p>You made the circuit diagram in InkScape!</p><p>You shouldn't drive current directly out of the microcontroller pins.</p><p>The majority of the microcontroller CPU cycles will go into managing multiplexing of the display (not calculating primes).</p></blockquote>

__After a little more work I have a functional device__ and it looks better than I expected. There are a few more features I want to add, and I want to work on the code some more, but I hope to be done tomorrow. The coolest part is that I've included an internal button which drives a pause/resume and speed-controller menu based upon the length of button presses! There's a lot of awesome stuff I want to write, but once again, I'll save it for the completed project page.

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__I rendered the cover sticker wrong and all the LEDs are mislabled.__ The first LED should be 2^0 (1), and the second should be 2^1 (2), etc. Also, 2^22 and 2^23 are mislabeled - oops! But the thing really does generate, differentiate, and display \[only\[ prime numbers. Once again, videos (including demonstration of the menus and the programming options) and source code will be posted soon.
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