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Fig. 3.
 
First ive components and formula resultant (1)
–
for a symmetric triangular waveform [8]:
)
2
(
2
2
2
2
2
]
)
9
sin(
9
1
)
7
sin(
7
1
)
5
sin(
5
1
)
3
sin(
3
1
)
sin(
[
8
)
(

+
+
+
+
+
Π
=
t
t
t
t
t
t
x
ω
ω
ω
ω
ω
Fig. 4.
First ive components and formula resultant (2)
As the above formulas show, the content of higher harmonics 
is much lower for the triangular waveform than for the rectangular 
one. This is expressed by the harmonics factor, the value of 
which is about 12% for the triangular and 45% for the rectangular 
waveform [9].
In order to have a more versatile possibility of shaping the 
test signal, an oscillator containing two independent function 
oscillators was built. Additionally, signals from the function oscilla
-
tors can be mixed together and analoguely multiplied (amplitude 
modulation). 
The described oscillator is shown here: (Fig. 5).

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Test-signal generators for Mindset MS-1000 electroencephalograph…
Fig. 5.
Oscillator schema

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Test-signal generators for Mindset MS-1000 electroencephalograph…
A regulator (U101, U102) converts a single +9V voltage 
source to symmetric +5V, -5V voltages, which are used to power 
the whole circuit [10][11].
The function oscillator is based on a quad operational ampli-
ier U201 (U301).
An integrator (U201d (U301d)) generates a triangular wave-
form. In order to do this, it has to cooperate with a threshold 
lip-lop (U201c (U301c)), on which a rectangular waveform is gen
-
erated [12] (the voltage spike is eliminated on U201b (U301b)).
The shaping circuit converts the triangular waveform to 
a sinusoidal one using diodes D203..D206 (D302..D306) [13]. 
Switch SW201 (SW301) makes it possible to select the 
desired type of the waveform.
Potentiometer R204 (R304) changes the frequency of the 
generated signal, and potentiometer R216 (R316) changes its 
output voltage level.
Potentiometer R401 mixes the signals. The amplitude modu
-
lation (ring modulator) is based on U501 integrated circuit and 
Q501 transistor (it is an analogue signal multipliier) [14].