Elenco Circuit Maker Skill Builder 125 - Manual (Page 41)

Project #77 Crazy Combo
Project #76 Switch & Store
The electricity supplied to your home by your electric
company is actually a changing voltage. Many
electronic products use rectifier circuits to convert
this into a constant voltage like a battery provides.
The music and space war ICs (U1 and U3) are
actually modules containing specialized sound-
generation ICs and other supporting
components (resistors, capacitors, and
transistors) that are always needed with them.
This was done to simplify the connections you
need to make to use them.
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Turn on the slide switch (S1) and the LED (D1) lights; it will not be very bright so
turn off the room lights or hold your fingers around it to see it better. Push the
press switch (S2) several times slowly; the LED and lamp (L1) go on and off.
Push the press switch many times quickly - the lamp still goes on and off but
the LED stays on. Next, remove the 470mF capacitor (C5) from the circuit - the
LED goes on and off now. Why?
Pressing the switch quickly simulates a changing voltage, which turns the LED
on and off. The 470mF capacitor can store electricity, and it combines with the
NPN transistor (Q2) to simulate a rectifier. This rectifier converts the changing
voltage at the press switch into a constant voltage, which keeps the LED on.
You can replace the 1KW resistor (R2) with the 100W resistor (R1). This makes
the LED a little brighter but you have to press the switch faster to keep it on,
because the lower resistance drains the capacitor faster.
Build the circuit shown. Turn it on, press the press switch (S2) several
times, and wave your hand over the photoresistor to hear all the sound
combinations. You can make the sound from the music IC louder by
replacing the 100W resistor (R1) with the 2.5V lamp (L1).
CM-125_Manual_031514.qxp_CM-125_Manual_031514 4/2/14 12:19 PM Page 41