Data Sheet

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Project 131
Back EMF
Build the circuit as shown.
Push the press switch
(S2) for a few seconds;
the fan spins but the red
LED (D11) doesn’t light.
When you release the
switch, the red LED
flashes. Wait until the fan
stops before pushing S2
again. The red LED is not
bright so dim the room
lights to see it better.
Use the preceding circuit, but remove the
blue jumper wire across base grid
locations C2 & E2. Press the switch the fan
spins. Release the press switch and now
both LEDs light. The LEDs are not bright
so dim the room lights.
See if the circuit has enough power to light
all the LEDS by removing the blue jumper
wire across base grid locations A2 & C2.
Project 132
EMF 2
Project 133 Lamp & Fan Independent
Build the circuit as shown.
Depending on which of the
switches (S1 & S2) are on, you
can turn on either the lamp (L4),
the clear motor (M4), or both
together. The color2 LED (D12) is
connected across the battery, so
it’s always on.
When the switch is pressed, electricity flows from
the battery (+), through the clear motor (M4) and
press switch, then back to the negative side (-) of
the battery, but does not flow through the LED
since it is backwards.
Electric current produces a magnetic field in the
motor and when the press switch is released, the
magnetic field collapses and generates an EMF
in the electromagnet coil windings. The voltage
produced by a motor when it is spinning is called
its Back Electro-Motive-Force (Back EMF).
The voltage can only power the LED for a second.
SC-3DMEG_Manual.qxp_SC-3Di_Manual_060816 6/19/17 7:33 PM Page 78