BEEP BEEP BEEP BEEP…
I hate waking up to an alarm clock. Especially on cold, dark winter mornings. My wife and I want to bike to work around dawn (so we can leave work and ride home before dark) which means we have to get up while it is still dark outside. This is painful with a regular alarm, but we’ve been experimenting with a prototype sunrise alarm built with an Arudino.
I’ve noticed that in the spring, when sunrise is getting earlier, it becomes easier to wake up before the alarm goes off. This feels wonderful: instead of feeling groggy, I feel rested and sometimes even energetic. In the fall, though, the trend reverses and it gets harder to wake up as it gets darker each morning. The sunrise alarm counteracts this trend by simulating an early sunrise, making sure the room is bright when it is time to wake up. This prompts the body to wake up naturally, rather than shocking it awake with loud noises.
The hardware for our prototype alarm is simple: I have a Lutron Maestro wireless light dimmer, and the Arudino is controlling it with a single IR LED. (You can read more about how to use the Arudino as a remote control in this post). The nice thing about controlling the dimmer wirelessly is that everything is 5 volts, and I don’t have to worry about 120 volt shocks.
The software uses the remote control signal code described in the earlier post and combines it with the example from the Arduino DateTime library. The DateTime example has code for setting the clock on the Arudino over USB. I extended the code to set the current time and also set the time for the alarm to go off. The Arduino waits for the alarm time to arrive, then starts sending commands to the light dimmer to slowly turn on the lights. Right now I have it turn them on over the course of 20 minutes.
At the moment this is just a prototype. I’ve been pretty happy with it so far, so at some point I’ll probably rebuild it using a bare AVR chip (so that I can use the Arudino for other projects). Here are some of the things I’ve noticed so far from using it:
- Using the regular lights in our room guarantees that it is bright enough to wake us up. It is a little too bright, actually. I might put lower-wattage bulbs in.
- I originally had it turn the lights on over 15 minutes. However, that felt too sudden. I kept waking up when it was already pretty bright. I slowed it down to take 20 minutes total; it ramps up to half brightness over the first 15 minutes then up to full brightness in the last 5 minutes. This seems to be more gentle. It might be worth experimenting with even longer periods of time, like 30 minutes.
- The Arudino Diecimila resets when it is connected or disconnected from USB, losing the time. However, if you just yank the USB cable it won’t reset. This is nice because otherwise I’d have to leave my laptop turned on all night just so the Arudino wouldn’t lose the time. Leave the IDE running and connected to the Arduino, then unplug the cable without disconnecting in software. You’ll need to have the Arduino powered from a dedicated power supply so there’s still power after the USB is unplugged.
- I originally had it run once and then stop, but that meant I had to set the alarm again every day which was a hassle. I changed it to automatically move the alarm time forward 24 hours, which is much more convenient (but also risky…if I forget and leave it running when we go on a trip, it will turn the lights on and leave them on).
- Bugs in this type of device are annoying. If you make a coding mistake, it might turn the lights on in the middle of the night, or turn them on and leave them on all day. It might also fail to work at all, letting you oversleep.
We’re still setting our regular alarm to go off a few minutes after the lights reach full brightness, just in case we don’t wake up. (I may add a speaker to the finished alarm to consolidate this). Most days I’m already awake or just lightly dozing when it goes the regular alarm goes off, which is good. It feels much more civilized than getting dragged out of bed in the dark by that awful beeping.
It is really easy to build a universal remote using an Arduino. With just an infrared LED, it can impersonate remotes for your TV, fans, lights, etc. and can let you easily incorporate these into your electronics projects. You won’t even have to solder anything or void any warranties.
For a project I’m working on, I need to emulate the remote for a Lutron Maestro light dimmer. It uses a modulated IR signal, which is a common way for remotes to communicate and is easy to generate with an Arduino. The basic scheme is simple: each command is sent as a series of pulses representing bits, which can be either 1 or 0. To send a 1, you rapidly blink the LED on and off at 38 kHz, and for 0 you leave the LED off. (The 38 kHz modulation makes the signal more resistant to interference from other light sources).
Decoding the Signal
To decode what the remote was sending, I used an oscilloscope and a small photodiode. The photodiode generates a small amount of voltage when light hits it, and responds to changes in light level quickly enough that the oscilloscope can draw a really nice plot of the signal. I have a Parallax USB oscilloscope, which is perfect for showing the command pulses and is just fast enough to find the modulation frequency. As an aside, I’m really happy with the Parallax oscilloscope for projects like this. It is simple to use and I love being able to save images to share with people.
Here’s what two of the commands from the dimmer remote look like. The top signal is the “fade lights up” command, and the bottom one is “fade lights down”:
I captured several different commands, then measured the length of all the pulses. Looking at all the commands, a couple patterns are obvious:
- The entire command takes 82.8 ms (after which it immediately repeats, presumably because I held the button on the remote down a little too long).
- The lengths of the on/off pulses are all multiples of 2.3 milliseconds (which means that the entire 82.8 ms command represents 36 bits of data).
- The last four bits are always 0, so really each command is four bytes long, followed by four 0 bits
The particular remote I’m emulating has five commands, and once they are decoded they look like this:
fade up = [255, 136, 130, 34]
fade down = [255, 136, 130, 20]
full on = [255, 136, 132, 184]
full off = [255, 136, 189, 18]
memory recall = [255, 136, 132, 183]
The one other missing piece of information is the modulation frequency which can be measured by zooming in on any of the pulses. This remote uses a frequency of 39.68 kHz. (In the plot below, it says the frequency is 3.96 kHz because I included 10 pulses in the measurement to increase accuracy)
Programming the Arduino
Using an Arduino makes the circuit really simple. I put an IR LED between pin 13 and ground. Since pin 13 has an internal resistor, that’s all that’s required. The code is also pretty straightforward:
/* Control a Lutron Maestro light dimmer */
#define BIT_IS_SET(i, bits) (1 << i & bits)
// LED connected to digital pin 13
const int LED_PIN = 13;
// Width of a pulse, in microseconds
const int PULSE_WIDTH = 2300;
// # of bytes per command
const int COMMAND_LENGTH = 4;
const int UP[] = {255, 136, 130, 34};
const int DOWN[] = {255, 136, 130, 20};
const int ON[] = {255, 136, 132, 184};
const int OFF[] = {255, 136, 189, 18};
const int RECALL[] = {255, 136, 132, 183};
void setup()
{
pinMode(LED_PIN, OUTPUT);
}
/* Modulate pin at 39 kHz for give number of microseconds */
void on(int pin, int time) {
static const int period = 25;
// found wait_time by measuring with oscilloscope
static const int wait_time = 9;
for (time = time/period; time > 0; time--) {
digitalWrite(pin, HIGH);
delayMicroseconds(wait_time);
digitalWrite(pin, LOW);
delayMicroseconds(wait_time);
}
}
/* Leave pin off for time (given in microseconds) */
void off(int pin, int time) {
digitalWrite(pin, LOW);
delayMicroseconds(time);
}
/* Send a byte over the IR LED */
void send_byte(int bits) {
for (int i = 7; i >= 0; i--)
{
if (BIT_IS_SET(i, bits)) {
on(LED_PIN, PULSE_WIDTH);
} else {
off(LED_PIN, PULSE_WIDTH);
}
}
}
/* Send a full command */
void command(const int bytes[]) {
for (int i = 0; i < COMMAND_LENGTH; i++) {
send_byte(bytes[i]);
}
off(LED_PIN, 4 * PULSE_WIDTH);
}
void loop()
{
command(UP);
delay(1000);
command(DOWN);
delay(1000);
}
Checking the Arduino with the Oscilloscope
After programming the Arduino, I used the oscilloscope to check the output of the Arduino vs. the original remote. On my first attempt, the wait_time in on() was too long, so the command was stretched out. I hadn’t accounted for the fact that the digitalWrite() calls would consume some time, so I just decreased wait_time until the length of the overall command was correct. As you can see, the final synthesized command overlaps exactly with the authentic one. The green signal on top is from the remote, and the blue signal on the bottom is the arduino:
Final Test
Once everything was ready to go, it was time for the last test: I tried using the Arduino in place of the remote and it worked! It was able to control the light dimmer flawlessly. This lets me finish my project, plus now that I have all the code written it should be easy to adapt to other remote control devices.