Manual

Project 70 Break the 2-Reflection Beam
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 mirrors.
Turn on the slide switch (S1); and carefully align the two mirrors 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: The mirrors must be precisely aligned for this to work. To help with this
alignment, do this in a dimly lit room, watch where the reflected light is shining, and
try to get it centered on Q4. Depending on the brightness of your room lights, you may
get better results without using the Q4 attachment, or by having brighter room lighting.
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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), but having some room light may make it easier to align
the mirrors (because less light is needed from the white LED).