In Japan there are many recycling shops where you can get old electronic junk for a cheap price. It's a very ecological way to learn about electronics, so I went ahead and bought a DVD remote controller at hard off.
Most remote controllers are based on infrared communication. Although humans can't see infrared light, I found out that the CCDs inside most cameras do. This can be useful for making your own infrared night vision camera (maybe a future post), or just for quickly checking whether your remote control is working or not.
Now let's go inside the device: remove the batteries and screws, and open it up by pressure. A remote controller typically consists of the following elements:
- A case made of ABS plastic.
- A PCB containing button switches and the control circuitry.
- A button panel made of silicone rubber. Each button has a layer of conductive paint underneath. When pressed it connects button switches on the PCB board.
Here is a sketch of the remote controller I got from hard off. It's a very simple circuit consisting of:
- Electrolytic Capacitor (47uF 10V): removes high frequency noise or peaks in the power supply. A general rule is to use one that supports at least double the normal voltage (10V > 2x3V).
- Ceramic resonator (4MHz): it works like quartz crystals but has bigger tolerance, it's cheaper and smaller (includes built-in capacitors). Used to create the carrier wave for infrared communication.
- Resistor (2.2 Ohm): not sure why such a low value.
- Transistor (C3203 NPN): for switching the LED on and off.
- IR LED: a LED that emits light in the infrared range (e.g., 950nm).
- IC: the chip where all the logic takes place. I couldn't identify which IC was used here, but I'm guessing it's something similar to the PCA8521. Button switches are wired to the IC, which (I guess) performs internally a loop (it could be done with flip-flops too) and polls the status of each button switch. Next, the IC selects the corresponding code from an internal ROM (customized during fabrication) and sends a modulated pulse wave through the IR LED.
In this post we are going to recycle the IR LED and save the remaining electronic components for a future circuit. An easy way to desolder components is to use a desoldering braid.
Once you desolder the LED, connect it to an Arduino digital pin using a resistor to limit the current running through (Arduino can handle up to 40mA). I'm using a 5V power supply and the LED's voltage drop is 1V so a 220 Ohm resistor will give me 18mA which is good enough to power the LED.
The final step wildly depends on your camera model. I have a Sony NEX-5 and fortunately there was a nice person that made the corresponding Arduino code public here. For different models you have to google a bit, and maybe modify existing arduino code, but it should not be too difficult (here you have code for Nikon cameras). Once you have taken interval pictures, put them together in a video with a command such:
mencoder -idx -nosound -noskip -ovc lavc -lavcopts vcodec=mjpeg -o output-rec.avi -mf fps=15 'mf://@files.txt'