Data Sheet

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B. Use the preceding circuit but
reverse the position of the press switch
(S2), 3-snap wire, 5-snap wire, and
each of the LEDs (D1, D2, & D10),
separately.
C. Use the project 2A circuit but
replace the press switch (S2) with the
phototransistor (Q4, “+” on right). Vary
the brightness of light shining on the
phototransistor and see how it changes
the brightness of the LEDs.
D. Use the project 2A circuit but
remove the press switch (S2) and
move one of the LEDs (D1, D2, or
D10) to where the switch was (place
the LED “+” on the right). The LEDs
may be a little dimmer now.
Educational Note: Reversing the
switch and snap wires has no effect.
LEDs only work in one direction, so
the red & green LEDs do not work in
reverse, but the yellow LED (D10) is a
bi-color LED, with separate red &
yellow LEDs in opposite directions, as
shown in its symbol.
Educational Note: All the electricity
flows through the LED that replaced
the switch, then divides between the
remaining two LEDs. The LEDs are a
little dimmer because the battery
voltage is split between them now.
Educational Note: The resistance of
the phototransistor varies depending
on how much light is shining on it,
brighter light lowers its resistance. In
this circuit the phototransistor restricts
the flow of electricity to all three LEDs
at once, so it takes very bright light to
make all three LEDs light. Some LEDs
need less electricity to turn on than
others, so they may turn on sooner.
A. Build the circuit, turn on the switch in the 9V battery holder, and push the
press switch (S2). The red, green, and yellow LEDs (D1, D2, & D10) light.
Note: The white jumper wire is used only as a spacer (so both snaps on the
yellow LED are on level 3); its right snap need not be connected.
Educational Note:
LEDs are light emitting diodes, which convert electrical
energy into light. The color of the light depends on the
characteristics of the material used in them.
SCSNAPINO_Manual_112816.qxp 12/30/16 2:00 PM Page 13