Elenco Snap Circuits SOUND &reg - Manual (Page 73)

Project 153 Adjustable Timer Tone Project 154
Photo Timer
Tone
Note that there is a 3-snap wire
under Q2, partially hidden. Turn
on both slide switches (S1) and
push the press switch (S2). You
hear a tone, which turns off after
a while. Push S2 again to restart
the keyboard and its timer. Use
the adjustable resistor (RV) to set
how long the timer keeps the
sound on for, it can be set for a
few seconds or very long. You
can change the tone that plays by
pressing keys on the keyboard
(U26).
Turning off the left slide switch
turns off the tone, but not the keys
or timer.
Use the preceding circuit, but replace
the 5.1k
W resistor (R3) with the
photoresistor (RP). The circuit works
the same way, but you can vary the
pitch of the tone by adjusting the
amount of light on the photoresistor.
Project 156
Adjustable
Delay Lamp
Use the preceding circuit, but replace
adjustable resistor (RV) with the
500k
W adjustable resistor (RV3). Set
the knob on RV3 to different positions,
press S2 to start the timer, and see
how long it takes for the color LED to
turn on. Turning RV3’s knob clockwise
gives longer delay, turning counter
clockwise gives shorter delay.
Project 155 Delay Lamp
Push and release the press switch (S2), then turn on the
slide switch (S1). Nothing happens at first, but after a few
seconds the color LED (D8) turns on. Press S2 to turn off D8
and reset the delay timer.
The adjustable resistor (RV) is used as a fixed resistor, and
moving its lever won’t have any effect.
This circuit works because capacitor C5
can store electricity. When you turn on the
circuit, electricity flows through resistor RV
into C5. When C5 gets full, electricity starts
flowing into transistor Q2, which turns on
the color LED. Pressing S2 empties C5,
and resets the timer. Capacitors C2 and
C7 also store electricity, but only small
amounts; if used in this circuit they would
appear to fill up instantly.
RV3 controls how fast electricity flows
into capacitor C5. Increasing RV3’s
value makes it take longer to charge
up C5.
-72-