Elenco Electronics EP-130 - Sine Wave Oscillator

-
1
5
0
-
This oscillator circuit produces a sine wave si
g
nal.
A
sine wave (or sinusoid) is a wave of pure sin
g
le
-
frequency tone. As an example, a 400Hz sine wav
e
is a wave that oscillates 400 c
y
cles in one secon
d
and contains no other frequency contents. Non-sin
e
waves
(
such as square wave or triangular wav
e
si
g
nals
)
have harmonics - waves with frequencie
s
that are multiples o
f
the sin
g
le-
f
requenc
y
fundamental wave. A non-sine 400Hz wave can
include the 400Hz wave (its fundamental wave)
alon
g
with an 800Hz wave (its 2nd harmonic wave)
and a 1200Hz wave
(
its third harmonic wave
)
.
A
square wave si
g
nal contains many harmonics.
E
xper
i
ence
d
tec
h
n
i
c
i
ans can test a c
i
rcu
i
t
b
y putt
i
n
g
a s
i
ne wave
i
nto
i
t an
d
li
sten
i
ng to
i
ts output - an
d
you can too. I
f
you put in a sine wave, and somethin
g
else comes out, the undesired harmonic
f
re
q
uencie
s
m
ust have been generated somewhere in the circuit.
The ke
y
parts of this circuit that produce a 400H
z
s
i
ne are
:
•A
0.
1
μ
F
capac
i
tor connecte
d
across term
i
na
ls
3 and 5 o
f
the trans
f
ormer. This
f
orms a tan
k
circuit that resonates at about 600Hz.
•
A
470
k
Ω r
es
i
s
tor to t
u
rn on th
e
base
o
f
th
e
t
ransistor onl
y
a little
.
•
An ad
j
ustable
f
eedback circuit that includes the
contro
l
an
d
t
h
e 0.05
μ
F
ca
p
ac
i
tor.
• A 100Ω resistor connected to the emitter. Thi
s
h
e
l
ps to sta
bili
ze t
h
e c
i
rcu
i
t an
d
k
eep t
h
e soun
d
f
rom being distorted
.
C
onnect the earphone to terminals 1 and 2 of the
transformer. Start with the control on maximum
(
10
on the dial
)
and slowly decrease the control settin
g
while listening to the tone quality o
f
the output. Be
f
or
e
t
h
e osc
ill
at
i
ons stop,
y
ou w
ill
reac
h
a po
i
nt w
h
ere
y
ou
h
ear on
l
y one tone.
Thi
s
l
ast c
l
ear-soun
di
ng tone
is
t
h
e s
i
ne wave.
R
epeat t
h
ese contro
l
a
dj
ustments unt
il
you
h
ave no trou
bl
e
di
st
i
ngu
i
s
hi
ng
b
etween a s
i
ne
wave and a distorted wave
.
No
t
es:
EXPERIMENT #12
8
:
S
INE WAVE
OSC
ILLAT
OR
Schematic
W
iring
S
equence:

1
-EARPH
O
N
E

2
-EARPH
O
N
E

3
-
28
-
109

4-94-106-124

5
-41-11
0

26
-4
0
-
93

2
7-
10
5

42-71

72-11
9

1
21-122