I wanted to play around with something IR remote-controlled, so I decided to make a remote-control mood light. There were two parts to the project: making the remote and making the light. For the remote, I tore down a remote control for a floor fan, removing all its insides, and replacing it with mine. I used a PIC12F1840 micro for the remote, mostly since I have a lot of these lying around. For the receiver, I used the same microcontroller. The enclosure for the mood light? a glass jar with some paper to diffuse the light (I am not too much into making enclosures). There were some interesting issues along the way, but now the project pretty much works. It has 4 high-brightness LEDs in it: White, Red, Green, and Blue.
Features? Currently the device has 2 modes, switchable using the “Mode” button. “On/Off” turns the device on and off, as expected. Settings are backed-up in EEPROM, so after any power loss, device comes back to the same mode and settings as it was in when it was last on. Fade mode fades between colors randomly, with adjustable speed and brightness. Adjustment is made using the “up”/”down” buttons. What is adjusted is selected using the “O” button. Increasingly bright white blinks after pressing the “O” button mean you’re in brightness adjustment mode. White, Red, Green, Blue flashes after pressing the “O” button mean you’re adjusting speed. Solid mode is a solid color, each of whose WRGB components is adjustable up/down using the “up”/”down” buttons. Current component is selected using the “O” button – when pressed, it flashes just that color for half a second to indicate what you’re adjusting. Selected color is saved when you switch modes, and restored when you re-enter solid mode. When in off mode, you can anter diagnostic mode by entering on the remote: “Up Down Up Down O O”. This shows some values using LEDs. Each value is preceded by a color to indicate the meaning. Then decimal digits of the value are sent, one at a time, using dimwhite blinks. The end of each digit is signified by a bright white blink. So to send 102 we’d see a dim white blink, a bright white blink, another bright white blink, two dim white blinks and a bright blink. For now only two vales are shown. Software version (color code green) and remote battery voltage (color code blue). The code is very modular, so adding new modes is dead easy.
The remote has 5 buttons, with black labels on grey background. I used a sharpie to color the background black, hiding the labels, except “on-off” and “mode.” Outlines of arrows were left grey next to two buttons and a circle next to third. So now the buttons are “Mode”, “Up”, “Down”, “O”, “On/Off”. Internally, the PIC reads the buttons by connecting them to pins RA0 – RA4, with internal pullups enabled and the other end of buttons grounded. This is where I hit the first snag. I was expecting to use Interrupt-On-Change to wake the PIC from low-power sleep when a button is pressed. No matter what I did, this feature would not work. I had used it on previous models of PIC devices successfully, and I’ve been through the doc over and over, with no results. I am now reasonably convinced that this must either be a mistake in the docs, or a silicon problem. Now this was a major problem. No low power sleep means no way to not run through another set of batteries every week. After some thoughts, I decided to measure the power consumption of the PIC while running on its LFINTOSC oscillator at 31KHz. It was less than 0.01mA. I guess this is low power enough. So now whenever I need to wait for button presses, I switch to LFINTOSC, and repeatedly read the port pins and look for changes.
I would love to have a working sleep mode, but sadly that appears impossible with this chip. The chip switches to 4MHz HFINTOSC-generated speed when sending a signal, and then back to low power mode when it is done with that.
The physical layer of the communication on the remote side is a single 940nm IR LED with a 38.6 KHz carrier frequency (generated by the CCP/PWM module). Data is sent in 8-bit bytes, MSB first. Each bit is a sequence of 0.5ms of modulated light, followed by 1 or 1.5 ms of darkness. 1.5ms means bit is 1, 1 ms means bit is 0.
For more detail: Remote Control mood light[/jar]