Manual

Project 68
Break the Reflection Beam
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Assembly:
1. Place base grid supports on base grid A.
2. Place parts on grids B&C, and install into base
grid supports on grid A.
3. Install remaining parts on grid A.
4. Add the Q4 attachment and mirror.
Turn on the slide switch (S1); and align the mirror so
that light from the white LED (D6) is reflected to
shine directly on the phototransistor (Q4), to shut off
the alarm. Now place your hand to block the
reflected beam and turn on the alarm.
Note: If too much room light shines on the
phototransistor then the alarm may never activate
(because the circuit doesn’t notice that the beam
was broken), so try dimming the room lights or
repositioning the circuit.
Modify the lower-left of the preceding
circuit to mount the mirror on a spring, as
shown. Turn on the slide switch (S1), and
align the mirror so that light from the white
LED (D6) is reflected to shine directly on
the phototransistor (Q4), to shut off the
alarm. Now push the mirror so that the
spring bounces it back and forth, turning
the alarm on and off as it bounces.
Project 69
Bouncy
Reflection
Beam
-52-
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