Elenco Circuit Maker Skill Builder 125 - Manual (Page 54)

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Project #107 Sonic Flasher
Project #108 Stay or Blink
Set the slide switch (S1) on, a space war sound plays and the LED
(D1) flashes. Cover the photoresistor (RP) and press the press switch
(S2) to change the sound. See how many sounds are programmed
into the space war sound IC (U3).
Build the circuit and turn on the slide switch (S1). The LED (D1) is dim,
and is actually flashing very quickly, and the speaker (SP) makes a
siren sound. Now push the press switch (S2) to connect the 470mF
capacitor (C5) to the circuit. The LED is brighter and stops flashing.
The signal from the alarm IC (U2) to the speaker is a changing voltage,
which is why the LED was flashing. The 470mF capacitor can store
electricity, and it combines with the NPN transistor (Q2) to make a
rectifier. A rectifier converts a changing voltage into a constant voltage,
so the LED stays on constantly instead of flashing.
Rectifiers are used to convert the AC voltage from the outlets in your
house to a DC voltage used by most of the devices in your house.
CM-125_Manual_031514.qxp_CM-125_Manual_031514 4/2/14 12:20 PM Page 54