Make Electronics

Experiment 11: A Modular Project

86 Chapter 2

Step    2:  Beyond  the Persistence of  Vision

If you substitute a much smaller capacitor, it will charge much more quickly,

and the LED will flash faster. Suppose you use a capacitor of 0.0047 μF (which

can also be expressed as 47 nanofarads, or 47 nF). This seems like an odd num-

ber, but it’s a standard value for a capacitor. This will reduce the capacitance by

a factor of more than 500, and therefore the LED should flash about 500 times

as fast, which should be about 1,000 times per second. The human eye cannot

detect such rapid pulses. The human ear, however, can hear frequencies up to

10,000 per second and beyond. If we substitute a miniature loudspeaker for

the LED, we should be able to hear the oscillations.

Figure 2-104 shows how I’d like you to make this happen. Please leave your

original, slow-flashing circuit untouched, and make a duplicate of it farther

down the breadboard, changing a couple of component values as indicated.

In the schematic in Figure 2-105, the new part of the circuit is in solid black,

while the previous section is in gray.

R1

R2

R3

Q1

C1

D1

R4

R5

R7

Q2

C2

L1

R6

6V

DC

Figure 2-104. The extra components which have been added at the lower half of the bread-
board have the same functions as the components at the top, but some values are slightly
different:

R4: 470K
R5: 33K
R6: 27K
R7: 100Ω
C2: 0.0047 μF
Q2: 2N6027
L1: 8Ω 1-inch loudspeaker

100

K

15K

0K

K

u)

10

10

00u)

K

0K

V

DC

Figure 2-105. The previous section that you

built is shown in gray. Just add the new

section in black.