Manual Part 2

Project 22 | TRANSISTOR AMPLIFIER

Project 23 | LIGHT & SOUND

Turn on the slide switch (S1). The color LED

(D8) is dim but the white LED (D6) is bright.

Turn on the slide switch (S1) to get a blinking light with funky

sounds. You can change the sound by removing the lamp (L4).

Part B: Remove either LED (D6 or D8) and

see what happens to the other one.

Part C: Swap the locations of the white

LED (D6) and the color LED (D8).

Part D: In the original circuit, replace the color

LED with the press switch (S2). Notice that

the white LED is only on when S2 is pressed.

The NPN transistor (Q2) is a current amplier,

meaning it takes a small current and makes it

larger. When a small current ows into Q2 through

the left branch (through D8), a larger current will

ow into Q2 through the right branch (with D6).

Green arrows show the current ow. This is why

the LED on the right side will be brighter than the

LED on the left side. In fact, the current in the right

branch can be as much as100 times larger than the

current in the left branch.

The left branch controls the right branch, so

removing D8 turns o󰀨 D6, but removing D6 does

not a󰀨ect D8.

A small electric current may be owing through

the color LED even when it appears to be o󰀨.

This small current, when it pass through the NPN

transistor (Q2) and gets amplied, can be enough

to keep the white LED on.

This circuit uses the blinking pattern of the color LED (D8) to

control the current owing through the lamp (L4) and melody

IC (U32), making them go on and o󰀨. The NPN transistor (Q2)

allows D8 to control the other electrical components. The

melody IC does not start up instantly, so the blinking pattern of

the color LED produces unusual sound e󰀨ects in the melody IC.