Tuesday, December 30, 2008

Arduino and LEDs

I’m a software developer by training and one aspect of the software that I’ve always developed is that it just lives inside a computer or network. It doesn’t interact with the real world. That’s been well and good for the last 20 years but of late I’ve been wanting to break out and have software that I develop effect some change in the physical world.

There have been fits and starts where I’ve tried writing code for some embedded system or chip but the mountain of basic knowledge thats needed to get started has always been overwhelming. I would read some book (like Embedded System Design on a Shoestring ) and while the books make it seem easy to get going, the projects would always die a quick and quiet death. There’s nothing wrong with Embedded System Design on a Shoestring or any of the other books I tried, many people have used them quite successfully. Unfortunately it just never clicked for me.

But that’s all changed.

I recently discovered the Arduino platform. The system provides a small microprocessor, a bunch of I/O pins, a USB connection and a very easy to use IDE. The basic features of the platform allow for most any type of interaction with the physical world that I can currently envision. I’m sure there will be some scenario that it won’t support but for right now, I’m very happy with the capabilities.

One of the problems that I encountered in the past was connecting an embedded system to a host platform. It may have involved a vendor specific hardware or something else that wasn’t supported on my systems. The Arduino uses a USB port. After installing the needed drivers on my OS X system, I was able to connect the Arduino without any problems. Seems way easier than other solutions.

The place that I see the Arduino really shining is with the IDE. It’s different that any other IDE that I’ve used but the interface is really straight forward and very easy to use. I was able to quickly try out one of the sample C programs that turns an LED on and off again. The thing that really got me was that it compiled, loaded and ran on the first try. This was just brilliant. Easy to use and works the first time. Outstanding.

When a friend asked for help with a project he was doing and told me that he’d like to have 3 LEDs turning on and off in a random fashion, I knew that an Arduino would be the perfect tool to use. I was able to rework the sample code for turning an LED on and off to work on this project.

The idea behind the project is to have an LED inside of a wax pumpkin where the LED would turn on and off like the light on a firefly. There would be three pumpkins on a small platform, hence the three LEDs.

Here’s the code for the project:


/*
* firefly multibutt illumination
*
* Copyright (c) 2008 Peter Kropf. All rights reserved.
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
* THE SOFTWARE.
*/


// all times are in milliseconds
#define SPIN_DELAY 10

#define ILLUMINATION_MAX 255
#define ILLUMINATION_MIN 0
#define ILLUMINATION_INCRIMENT 5

#define MAX_ILLUMINATION_TIME 2000
#define MIN_ILLUMINATION_TIME 500

#define MAX_DARK_TIME 10000
#define MIN_DARK_TIME 2000


#define LED_COUNT 6
#define LED_OFF 1
#define LED_ON 2
#define LED_SPINUP 3
#define LED_SPINDOWN 4

int led_pin[LED_COUNT] = {3, 5, 6, 9, 10, 11};
int led_state[LED_COUNT] = {LED_OFF, LED_OFF, LED_OFF, LED_OFF, LED_OFF, LED_OFF};
int led_spin[LED_COUNT] = {0, 0, 0, 0, 0, 0};
int led_level[LED_COUNT] = {0, 0, 0, 0, 0, 0};


void setup()
{
randomSeed(analogRead(0));
}


void loop()
{
for (int led = 0; led < LED_COUNT; led++) {
switch (led_state[led]) {
case LED_OFF:
if (led_spin[led] > SPIN_DELAY) {
led_spin[led] -= SPIN_DELAY;
} else {
led_state[led] = LED_SPINUP;
}
break;

case LED_ON:
if (led_spin[led] > SPIN_DELAY) {
led_spin[led] -= SPIN_DELAY;
} else {
led_state[led] = LED_SPINDOWN;
}
break;

case LED_SPINUP:
if (led_level[led] < ILLUMINATION_MAX) {
led_level[led] += ILLUMINATION_INCRIMENT;
} else {
led_level[led] = ILLUMINATION_MAX;
led_state[led] = LED_ON;
led_spin[led] = random(MIN_ILLUMINATION_TIME, MAX_ILLUMINATION_TIME);
}
break;

case LED_SPINDOWN:
if (led_level[led] > ILLUMINATION_MIN) {
led_level[led] -= ILLUMINATION_INCRIMENT;
} else {
led_level[led] = ILLUMINATION_MIN;
led_state[led] = LED_OFF;
led_spin[led] = random(MIN_DARK_TIME, MAX_DARK_TIME);
}
break;
}

analogWrite(led_pin[led], led_level[led]);
}

delay(SPIN_DELAY);
}

The code is pretty straight forward. Each of the LEDs has a particular state that it’s in: off, on, spinning up or spinning down. That’s tracked in the led_state array. The led_level array holds the current level of illumination for each of the LEDs and the led_spin array holds the random amount of time that the LED will remain on or off. The rest of the code manages the arrays, sets the current level of the LEDs and waits for a small delay before doing it all over again.

Note that the code is currently setup to illuminate up to 6 LEDs since that’s the number of digital I/O lines on the Arduino that supports pulse width modulation, PWM. PWM is how the Arduino is able to vary the light level produced by the LEDs.

Here's a short video I took while working on the LED timing. It shows only one LED instead of the three that were used in the finished project.

video

With this project successfully completed, I’m looking forward to my next project: having a flashing light turned on when a specific voicemail box on a Asterisk based phone system has messages waiting. This’ll involve connecting an Arduino to ethernet and controlling a 120v circuit. I can’t wait.

Saturday, December 27, 2008

Curmudgeon

There are times that I think I'm turning into an old curmudgeon. Complaining about the kids riding up and down the street on their two-stroke gas powered scooters or bemoaning some new technology like twitter. It seems that as we get older, there's a mindset that's easy to adopt where things that are different or new are somehow bad. And when I realize that I'm there, I don't like it.