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February 27th
Circuit Board

This section gives some basic electronics and robotics information along with helpful links. I also detail a lot of my projects. For most of them I've included schematics. I use ExpressSCH for drawing them and ExpressPCB for designing circuit boards. They are a free package from You can download for free and get your boards professionally manufactured for very reasonable prices. Of course, with the final layout you can also etch your own boards at home if you choose.

June 18, 2011

My Second Microcontroller Project

My second project, also utilizing an ATTINY13, expanded on the first by adding a second LED and push button switches to activate/deactivate them. It was based on a simple project from a book I had bought, but wasn't much more than my first project so I modified it. One button causes the LEDs to alternately flash and the other button causes them to pulse back and forth from dim to bright. It taught me how to use software PWM (pulse width modulation) which will eventually be useful for controlling servos. I got a lot of help from forum members over at It's a great resource for anyone interested in AVR. After building it on the breadboard, I wired it up permanently on a small perfboard which was then screwed directly onto a 3 AAA battery holder. I plan to eventually etch my own board for this, so I've included the PCB tracing if you want to try.

Here is the code for the project, including a simple technique for debouncing the switches. I've commented it fully to make it pretty clear:

* Created on: June 17, 2011
* Author: Brian Redmond

#include <avr/interrupt.h>

#ifndef F_CPU
     #define F_CPU 1000000UL

unsigned char x=0; // for status of blinking
static unsigned char b=1; // starting (and MIN) value for OCR0A
static uint8_t dir; // for stepping b which is added to OCR0A. Will change to down when b reaches 254 and back to up when b reaches 1
unsigned char z=0; // for status of PWM fading

enum { UP, DOWN };

ISR(TIM0_COMPA_vect) // Turns off both LEDs when TCNT0 matches OCR0A

ISR(TIM0_OVF_vect) // Turns on both LEDs on TCNT0 overflow
   PORTB=((0<<3) | (0<<4)); // +5 V turns off LEDs because they are sinked, not sourced, so a 0 at the bit turns them on
   switch (dir) // increments b (LED brightness) to 254 then decrements to 1
      case UP:
         if(++b == 254)

      case DOWN:

int main(void)
   DDRB = 0x18; // Pins 2 and 3 as output (5 and 6 are input)
   PORTB = 0x1B; // +5V to pins 2 and 3 (turns off sinked LEDs), enable internal resistors on pins 5 and 6

      if(!(PINB&(0x01))) // Blinking LEDs - button 1
         cli(); // Disable interrupts
         z=0; // Must reset pulsing variable in case blink button was pressed while pulsing was on
         if(x==0) // Blinking is off so start blinking
            PORTB = 0x0B; // Turn on LED 1 while turning off LED 2
            while((PINB&(0x01)) && (PINB&(0x02))) // Loop until either button is pressed
                  PORTB^=(0x08 | 0x10); // Toggle LEDs
         else // Blinking is on, stop
            PORTB=0x1B; // Turn both LEDs off

      if(!(PINB&(0x02))) // Pulsing LEDs - button 2
         x=0; // Must reset blinking variables in case pulse button was pressed while blinking was on
         dir=UP; // Start LEDs dim and pulse up
         if(z==0) // LEDs are not pulsing
            PORTB=0x1B; // Make sure both LEDs are off first
            TIMSK0 |= ((1<<OCIE0A) | (1<<TOIE0)); // Use compare and overflow interrupts
            TCCR0B = ((1<<CS00) | (1<<CS01)); // Prescaler 64
            TCNT0=0; // Reset counter
            sei(); // Enable interrupts
            while((PINB&(0x01)) && (PINB&(0x02))) // Loop until either button is pressed. Nothing in loop since everything is handled by interrupts

         else // LEDs are pulsing, stop
            cli(); // Disable interrupts
            z=0; // Reset z to not pulsing
            PORTB=0x1B; // Turn off both LEDs

This schematic shows the switches for toggling the LEDs as well as a reset switch, all powered by 3 AAA batteries. All three switches are momentary pushbutton.

Here is the breadboard layout.

PCB trace
Here is the PCB tracing for home etching. The buttons are 6mm x 6mm B3F series (Digikey part number SW403-ND). These are smaller than the buttons I used because I had these already on hand. Full-size PNG file is here. Printed size should be 2 inches by 1.5 inches.

PCBHere is the PCB layout. C1 is a 0.1uF capacitor and the resistors I used were 470 ohm. The 3-holed component is a power switch and the square connector is a Molex KK for power in from the batteries. The red connection shows where you'll need a top-layer jumper wire if you etch at home. If you want to download the actual ExpressPCB file, you can do so here.

Final build
Here is the finished project. Home etching would eliminate the rat's nest of point to point wires underneath.

Here's a video of the finished project.

Other Projects
An audio controlled servo - June 1, 2011
My first microcontroller project - May 17, 2011
I built a motion controlled cat fountain - March 24, 2011
A 555 timer project - December 17, 2009
A basic line-following robot - March 11, 2009