Data Sheet
-29-
22. LED, the Check Valve Light
Build the circuit shown on the left making sure the heart LED (69) is
in the correct direction. Press the switch (62) to turn it ON and OFF.
Reverse the heart LED (69) and repeat. Notice that the heart LED (69)
does not light when in the circuit in the reverse direction, demonstrating
how LEDs only allow current to ow in one direction.
23. Alarm Switches
Replace the switch (62) with the reed switch (83). Move the magnet (7)
towards the reed switch (83) and the heart LED (69) will turn ON. Move
the magnet (7) away and the heart LED (69) will turn OFF. House alarms
sometimes use reed switches to detect when a door or window is open.
24. Reed Switch vs. Mechanical Switch
Replace the reed switch (83) with the press switch (61). Press and hold
the press switch (61). The heart LED (69) will be on while you hold down
the press switch (61) and will go off when you release the press switch
(61). One of the benets of reed switches over mechanical switches
like the press switch (61) is reliability/lifetime. Mechanical switches can
wear out more quickly as you use them, and some studies show that
reed switches can be used 10,000 times more often than mechanical
switches before they wear out.
25. 1k Ohm Resistor
Replace the 100 Ohm (W) resistor (41) with the 1kW resistor (42). You
will nd that the heart LED (69) is dimmer. The letter “k” in 1kW stands
for kilo, which is a prex that stands for 1000. So 1kW is equal to
1000W, which is 10 times greater than 100W, which is why the heart
LED (69) gets dimmer when you replace the 100W resistor (41) with a
1kW resistor (42).