Should you be lucky enough to have an oscilloscope perched on your
workbench, you can see that a 38 kHz square wave looks something like
the one shown in Figure 9-2. But don’t worry: You don’t have to have an
oscilloscope to tune your IR transmitter. We tell you how to tune it in the
upcoming section, “Trying It Out.”Scoping out the schematic ................................................................
You put together two breadboards for this project: one that transmits and
one that receives and sounds off.First, you can see the schematic for the board that goes in what we call the
silent pumpkin(the one with the transmitter in it) in Figure 9-3.Here’s the nitty-gritty of the schematic elements for the silent pumpkin:The IR LED (LED2)is one of the key components of this circuit; the pur-
pose of the rest of the circuit is to send an electrical current, which
turns on and off at a frequency of 38 kHz, through this LED. This current
causes the LED to transmit IR light that turns on and off at a frequency
of 38 kHz (38,000 times a second: so fast you can’t even see a flicker).Figure 9-2:
A square
wave on an
oscilloscope
screen
looks like
this.