Manual
-25-
19. Switches in Series
Build the circuit, press the switch (62), then hold
the press switch (61). The LED (69) will turn on.
Release the press switch (61), then the light will
turn off. This kind of circuit could be used in a hotel
room where your key card must be inserted in a
card holder near the door to enable a closed circuit,
but you still need to turn on switches in the room
to close the circuit and turn on lights or devices in
the room.
20. Electronic ‘AND’ Gate
Build the circuit to the left. Note that the lamp (76)
only turns on when both the switch (62) and press
switch (61) are ON. In digital electronics there are
seven logic gates: AND, OR, XOR, NOT, NAND,
NOR, and XNOR. This circuit represents an AND
gate. If ON = True and OFF = False then an AND
gate is best dened as: The output is TRUE only
when both inputs are True. Therefore, the two
inputs represented by the press switch (61) and
the switch (62) must both be ON (TRUE) in order
for the output represented by the lamp (76) to be
ON (TRUE).