Elenco Upgrade Kit SC500 to SC750 - Manual (Page 55)

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Project #621
OBJECTIVE: To decrease the speed of a motor using an SCR
and transistor.
Two-speed Motor (II)
Instead of increasing the motor’s speed as in project #620, pressing the
press switch (S2) decreases the speed. In this circuit, the transistor
(Q2) is in parallel with the SCR (Q3). Pressing S2 turns on Q2 and the
voltage across the motor (M1) decreases.
Project #622
OBJECTIVE: To show the effects of current flow.
Current Flow
Set the meter (M2) to the LOW (or 10mA) position. Turning on the
slide switch (S1) connects the motor (M1), meter and 2.5V lamp (L1)
to the lower battery (B1) pack. The motor rotates clockwise and the
meter deflects right. Now turn off the slide switch and press the press
switch (S2). Now, current from the upper battery causes the motor to
rotate in the opposite direction. If you place the batteries in series by
turning on the slide switch and then pressing the press switch, only the
bulbs (L1 & L2) light.
!
WARNING: Moving parts. Do not touch the fan or
motor during operation. Do not lean over the motor.
!
WARNING: Moving parts. Do not touch the fan or
motor during operation. Do not lean over the motor.
To learn more about how circuits work, visit www.snapcircuits.net or page 85 to find out about our Student Guides.