Manual

Place a small piece of
paper between these 2-
snap wires, and position it
to block the light between
D6 and Q4.
Build the circuit as shown; note that there are five vertical snap wires (V1) standing up. Place a small
piece of paper between the two 2-snap wires as shown, and position it to hang down and block the
light between the white LED (D6) and the phototransistor (Q4). Place the circuit in a dimly lit room.
Turn on the slide switch (S1); the white LED should be on, but there should be no sound. If there is
sound, move the circuit away from room lights, or adjust the position of the piece of paper until the
sound is off.
Now blow on the lower (hanging) side of the paper, moving it up enough for light from the white LED
to reach the phototransistor, which makes the horn (W1) sound. Adjust the position of the paper as
needed so that blowing on it triggers the “high wind alarm”.
Use the preceding circuit, but remove the two
2-snap wires and paper, and instead place a
single 2-snap one snap down on the vertical
snap wire, as shown. The 2-snap should be
blocking the light between the white LED (D6)
and the phototransistor (Q4), and the sound
should be off.
Gently toss a stabilizer at the loose side of the
2-snap (the “target”). When you hit it and knock
it out of position, light from the white LED
reaches the phototransistor and triggers the
horn (W1), indicating success.
Project 138
Hit the 2-Snap
-71-
Project 137 High Wind Alarm