Elenco Upgrade Kit SC500 to SC750 - Manual (Page 54)

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Project #619
OBJECTIVE: Control bulbs L1 & L2 with an SCR and
transistor.
SCR & Transistor
Switch
Turn the slide switch (S1) on and then press the press switch (S2), both
bulbs (L1 & L2) light, but only L2 stays on when S2 is released. To stay
on, the transistor (Q2) requires a continuous voltage but the SCR only
needs a pulse. The speaker (SP) may not make any sound.
Project #620
OBJECTIVE: Increase the speed of a motor using an SCR and
transistor.
Two-speed Motor
If you turn on either switch (S1 or S2) alone, nothing happens. But if
you turn on the slide switch (S1) and then press the press switch (S2),
the lamps (L1 & L2) light and the motor (M1) spins. The SCR (Q3)
keeps the 6V lamp (L2) on and the motor spinning after you release
the press switch. If you hold the press switch down, then the 2.5V
lamp (L1) stays on and the motor spins faster.
!
WARNING: Moving parts. Do not touch the fan or
motor during operation. Do not lean over the motor.