- 1). Select an infrared LED. In its data sheet, note the voltage and power requirements. If you're interested in a particular IR wavelength, pay attention to the LED's specifications.
- 2). Select a current-limiting resistor for the LED based on the electrical requirements from Step 1. The resistance in ohms should equal the LED's operating voltage divided by its current in amperes. The power rating for the resistor in watts should be greater than current squared times the resistance. For example, if your calculation yields .3 watts, use a ½ watt or 1-watt-rated resistor.
- 3). Select a battery or DC power supply with output voltage equal to the LED's operating voltage.
- 4). Using the hobby knife, bore a hole in the perfboard large enough to mount the switch. Mount the switch using its hardware.
- 5). Insert the LED into the perfboard. Locate it far enough from the switch that it won't interfere with the switch's operation, but close enough that wiring will be convenient. Insert the resistor into the perfboard such that one lead of the resistor is adjacent to one of the LED's anode. Note that the cathode is marked by the LED's flat side, so the anode is the opposite side. Solder the anode to the resistor lead. Solder the LED cathode lead to the switch.
- 6). Wire the DC power supply or battery holder to the switch and resistor. Connect the negative supply to the unconnected side of the switch. Connect the positive side to the unconnected resistor lead. Solder the connections and trim excess wire.
- 7). Plug the power supply in or insert the battery and turn the switch on.
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