Hardware Reference
In-Depth Information
he light beam sensors are based on of a pair of components - an emitter and a detector. In
order to measure the speed or direction an object (in this case a bird) is moving, you will need
to build two pairs.
The Required Parts
It's quite easy to build your own light beam detectors; parts are readily available for less than £1.
here is a range of many diferent LEDs and phototransistors that all work in a similar way.
hey're available from the typical electronics suppliers online. Although it's possible to sub-
stitute parts, I have tested only the following components. Because you are wiring up elec-
tronics to the Raspberry Pi, I suggest that you use PiFace Digital to provide additional
protection, and enough current to drive the emitters. You will need
❍
2 IR LEDs, such as part number OSRAM - SFH484-2 - INFRARED EMITTER, 5MM,
880NM
❍
2 IR photodetectors, such as part number QSE113 - INFRARED PHOTOTRANSISTOR
❍
2 1k ohm resistors
❍
2 330 ohm resistors
❍
Wire
Wiring Up the Emitter
he emitters are made using an infrared LED. Infrared LEDs are much the same as normal
LEDs, but they emit infrared light rather than the typical red, yellow, blue and so on LEDs you
might see on electronic devices. Here's a reminder of things to consider when using LEDs:
❍
LEDs work only one way around, so you need to ensure that the correct leg is con-
nected to a +ive (positive) power supply.
❍
LEDs can be damaged by too much voltage, so you may need a resistor in series.
For most LEDs, the longer lead of the LED (called the
anode
) should be connected to the
power supply. However, if you have the SFH484-2 IR LED, the longer lead is the cathode and
should be connected to 0V (also sometimes called
ground,
negative
or
-ive
).
Connect the anode of the LED to the 330 ohm resistor. Connect the other side of the resistor
to the power supply as shown in Figure 17-2.
