Elenco Electronic Playground 50-in-1 Experiments - Manual (Page 27)

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Connect the wires according to the Wiring Checklist.
Although there is a closed circuit with the battery, 1K
Ω,
LED, and transistor, no current will flow since the
transistor is acting like an open circuit (with no base
current the lever arm remains shut). Press the switch; a
base current now flows and opens the lever arm,
resulting in a large collector current which lights the LED.
The transistor is being used as an electronic switch.
Although there is still a normal switch in this circuit, there
could be many electronic switches controlled by one
normal switch.
EXPERIMENT #13: The Electronic Switch
Wiring Checklist:
o 41-to-27-to-56
o 55-to-45
o 44-to-15
o 17-to-26
o 40-to-1
o 2-to-16
Schematic