Design and Implementation of a Multi-function
Generator
Rana Ramli and Alaa Elkhair
Electrical and Electronics Engineering Department
University of Khartoum
Khartoum, Sudan
rana_ramli@yahoo.com, lola-sun07@hotmail.com
Abstract— This paper describes the design, implementation and
testing of a low cost multi-function generator that is able to
generate sinusoidal wave, triangle wave and square waves. The
user can select the desired waveform. Moreover, the user can
change the amplitude of the generated signal easily over a wide
range. In-addition, the user can change the frequency for the
generated signal over an acceptable range for several
applications. One last feature is the ability of measuring both the
frequency and the amplitude of the selected signal and display
them on an LCD, this eliminate the need for another device, to
measure or display the amplitude and the frequency of the signal.
The multi-function generator was designed by using two methods
microcontrollers and op-amp
Keywords-Functiongenerator;Frequency;Amplitude;Oscillator.
I.
INTRODUCTION
A function generator is usually a piece of electronic test
equipment or software used to generate different types of
electrical waveforms over a wide range of frequencies [1]. It is
considered as a vital component in testing and developing
electronic systems, whether in service bench or in research
laboratory. Function generators have variety of application,
such as checking the stage gain, frequency response and
alignment in receivers, providing an excitation to the
electronic measurement systems as well as providing carrier
frequency in many of modulation techniques.
Function generators are well none since 20 years ago but
all the available ones have limitations. The high cost, the need
of other devices such as an oscilloscope to display the signal
and the non-accurate results that may obtained leads to further
investigation and research to develop new methods and
designs to implement multi-function generators. Even, the
available multi-function generators' designs are usually hidden
from researchers so that they need to use their own knowledge
and background to innovate their own designs.
When attempting to design a multi-function generator, the
designers should focus on the integration between hardware
and software implementation. The hardware portion is
responsible for generating the signals while the software part
is responsible for calibrating, measuring and displaying the
amplitude and the frequency of these signals.
The proposed multi-function generator was designed and
implemented from the scratch with the aid of the standard
methods and techniques known to generate the signals. The
integration of the software with the hardware was upgraded
using a common and powerful component which is the
Microcontroller.
The proposed system model is composed from (1) the
generator stage, (2) electronic circuit stage and finally (3) the
microcontroller stage.
In these paper we emphasized on the part that is related to
the measuring and displaying the parameters of the generated
signal as this is a new feature with is not found in all the
available generators.
The rest of this paper is organized as follows: some
background knowledge about the characteristics oscillators
and multivibrators is given in Section II below. The design
part is explained in Section III. Experimental results are
discussed in Section IV. Finally the paper is concluded in
Section VII.
II.
BACKGROUND
A signal generator consists of two important main blocks:
oscillator and attenuator [2]. Generally the oscillator uses an
active device such as an operational amplifier, the output is
fed back in phase with input and this positive feedback causes
regeneration action resulting in an oscillation.
When an electronic circuit is activated, there are electrical
noises present that span the electrical frequency spectrum. If
the noise is amplified and the output of the amplifier is
connected to a positive feedback network, an oscillator can be
created [3]. The positive feedback network is designed to
select a signal at one frequency. This signal is coupled back to
the input in proper phase so it reinforces the signal present at
the input. As this process of amplifying and positive feedback
continues, the selected frequency becomes the dominant signal
in the circuit; the result is a sinusoidal signal.
The building block of the non-sinusoidal oscillators is a
special electronic circuit called multivibrator, multivibrators
belong to a class of regenerative or positive feedback circuits
that have two states[4], based on these two states multivibrator
are classified into several types one of these types is known as
Astable or free-running multivibrators which have two quasistable output states and the circuit switches back and forth
from one state to another, remaining in each state for aperiodic
time determined by the circuit element [5]. Because of this
switching action of voltage or current between two states
astable multivibrators generate square waveforms.
As it is known, to adjust the shape of the required signal and
to set its amplitude and frequency , usually we connect the
generator with oscilloscope ,in this new designed function
generator we eliminate the use of oscilloscope by allowing the
user to select the shape of the signal and to enter the desired
amplitude and frequency by keypad.
III.
DESIGN
The block diagram illustrates the high level design of the
multifunction generator is shown in Fig.1, which consists of
several blocks.
Generate
the signal
and select
the shape
Change
the
amplitude
and the
frequency
Measure
and
display the
frequency
Measure
and
display the
amplitude
Possible combination of A0 and A1 are shown in the table
below:
TABLE1. COMBINATIONS OF A0 AND A1.
A0
0
0
1
1
A1
0
1
0
1
Output
Sinusoidal
Square
Triangle
None
After one of the signals was selected by using the
multiplexer it is necessary to change the amplitude of the
signal, to accomplish this, the signal was applied to a noninverting op-amp with variable feedback resistor.
For the triangle and square wave the frequency was
changed using by a potentiometer(R16) and by adjusting its
value together with a capacitor (C2) the frequency of the signal
can be changed, that is because the capacitor which is connect
to the positive input of the op-amp(figure 2), will charge
through (R16) and the voltage across it will rise exponentially
with a time constant of RC when the positive input of the opamp reaches the threshold voltage ,the capacitor will start to
discharge and its voltage will decrease exponentially, so by
changing the value of the capacitor and potentiometer the time
constant well change causing a change in the frequency.
VDD
Figure1. Multi-function generator block diagram.
A. Signal generations, frequency and amplitude change using
hardware components:.
In this design three types of signals (sine wave, triangle
wave and square wave) were generated from three circuits
then an analog multiplexer was used to select one of them.
Two approaches were used to generate the signal; the first
approach rely on hardware components to build an oscillator
circuit, in the second approach the microcontroller was used to
generate the signal
The design that used the first approach based mainly on the
oscillation principles as three types of oscillators were used to
generate three shapes of signals.
Several sinusoidal oscillators were tested both in simulation
and laboratory, Wien bridge oscillators was noted for high
stability and low distortion, thus it was used to generate the
sinusoidal waveform.
To generate the square and the triangle waves two op-amps
were used, the first op-amp is like an Astable multivibrator
that will generate a square wave from the triangle wave. A
second op-amp is set up as an integrator that creates a triangle
wave from the square wave.
After generating the signals from the circuits they were
combined as inputs to the analog multiplexer then one of them
can be selected as output. To accomplish this, ADG509F
analog multiplexer was used. The ADG509F switches one of
four differential inputs to a common differential output as
determined by the 2-bit binary address lines A0 and A1.
R8
C4
15V
VDD
7
14
6 100k Ω 16nF
R6
VCC
100k Ω
0
C3
15V
VCC
7
16nF
1
5
U3
3
6
8
2
2
D1
R 10
0
10k Ω
4
9
R5
10k Ω
Ke y =A
R7
10
10k Ω
50%
VEE
12
VEE
-15V
1NR4001
9
1147k
DΩ
2
0
741
4
S1A
5
S2A
6
S3A
7
S4A
13
S1B
12
S2B
11
S3B
10
S4B
1
A0
16
A1
R VCC
1
15V
VCC
VCC
15V
VCC
U2
7
4
0
R3
14
1
5
U1
3
47k Ω
5
OPAMP_3T _BASIC
1
741
R2
150nF 50%
Key=A
15
0
-15V
VCC
15V
VCC
7
1
5
U5
3
6
15
2
16
10k Ω
0
VSS
VSS
C1
1uF
13
R 14
10k Ω
R 13
4
9
GND
3
15V
0
C2
DB
ADG509F
VCC
6
2
8
17
VSS
R11
50kΩ
DA
DCD
VCC
2
EN
1N 4001
10k Ω
50%
Ke y =A
U4
VDD
R 12
50k Ω
50%
Ke y =A
4
8
18
VEE
AD507JH
VEE
-15V
100k Ω
3
R15
100kΩ 50%
Key=A
Figure 2 . The final design
B. Signal generations, frequency and amplitude change using
software.
In the previous work the signal was created using op-amp and
its frequency and amplitude were changed using several
components, now the signal can be generated by using
ATMEGA32 microcontroller with the ability to select the
waveform of the signal , its frequency and amplitude using
keypad.
The function that was used to generate the square wave is:
Void send- square- wave
{ float dt,t,x,v, y;
X=period*y
V=0.0
T=0.0
Dt=delay-time-us*1.0e-6;
Continue transmitting=1;
While( continue transmitting= =1)
{v=AMP*t/period
THE REMAINING OF THE LOOP GRANTEES THE
INCREAING OF THE AMPLITUDE.}
The user will enter amp and t to select the amplitude and the
frequency respectively.
With the same procedure a second and third functions were
written to generate the sinusoidal and the saw tooth waves the
only different is in the variables period and v
For the sinsoudal signal
Period =1.0/freq
V=0.5*amp*(1=sin(t*2*freq)
For the saw tooth
V=amp*t/period
In general the code contains the following main functions:
Name
Purpose
Keypad read
Read the numbers entered by
the keypad
Select letter, forward and
Allow the user to press the
back space
letters 7,8,9 to select the
shape of the signal
IsNumeric
Checks whether the buffer
contains only numeric values,
return 1 if all characters in the
range 0-0
Return 0 if any is not numeric
Get-Item string
Allows the user to enter,
through the keypad the string
for given data item
Square, triangle and sine
Generate the various types of
waves
Perform-Data-Entry
Allows the user to enter all
the data items need for the
operation of dispening
,machine
To conclude, the operation is as follows: At the first the saw
tooth signal will be generated as default then the user should
press 7,8,9 ( this will be displayed on the LCD as 1,2 and 3) to
select sinusoidal signal, square signal and saw tooth signal
respectively, to switch from one signal to another the push
bottom should be pressed finally press(+).
C. Amplitude and frequency measurement and display .
However to make the use of the designed function generator
more convenient another new feature was added , this feature
is that the device can measure the amplitude and the frequency
of the signal and display them on an LCD.
To measure the frequency, the Timer1 (TMR1) in
PIC16F877microcontroller was used to Count the 'zero'
crossings of an input signal applied to RC0 pin (15), for 1
second therefore counting the frequency of the signal. The
input signal's frequency is then displayed on a 16*2 LCD. The
1s delay is created by generating a perfect 1,000,000 cycles (it
takes 1μs for one cycle at 4.000000 MHz).this was illustrated
in the following piece of the program
void main ( ) {
int cycles8, cycles;
int32 freq;
int32 RealFreq;
long freqc_high;
long freqc_low;
while (TRUE) {
cycles8=0;
cycles=0;
freqc_high=0;
t1_overflow=0;
set_timer1(0);
setup_timer_1(T1_EXTERNAL|T1_DIV_BY_1);
while (cycles!=0xFF) { //true=3, false=4
cycles8=0; //1 cycle
// start inner loop
while (cycles8!=0xFF) { //true=3, false=4
if (t1_overflow)//true=2,false=3
t1_overflow=0;freqc_high++;}//6 cycles
else
{delay_cycles(5);}
delay_cycles(1); //x
cycles8++; //1 }
This research used a HD44780 based character LCD to display
the measured amplitude. The voltage to be measured is fed to
one of the 8 analog channels. The reference voltage for A/D
conversion was chosen to be the supply voltage Vdd (+5 V).
Since the PIC port cannot take more than 5v input directly, the
input voltage was scaled down using a simple resistor divider
network. A 5.1V zener diode connected in parallel between
the port pin AN2 and the ground provides protection to the
PIC pin in case the input voltage accidentally goes beyond
20V. The following piece of code illustrate the measuring of
the amplitude
unsigned int ADC_Value, DisplayVolt;
char *volt = "00.0";
Do{
ADC_Value = ADC_Read(2);
DisplayVolt = ADC_Value *3;
volt[0] = DisplayVolt/1000 + 48;
volt[1] = (DisplayVolt/100)%10 + 48;
volt[3] = (DisplayVolt/10)%10 + 48;
Lcd_Out(2,5,volt);
delay_ms(100);
}
while(1);
The remaining part of the code is the ASCII representation of
characters to be displayed on LCD.
By integrating all the above parts and microcontroller a
powerful new multifunction generator was designed, the final
stage is to implement this design.
IV.
(a)
RESULTS AND DISCUSSION
The proposed system has been implemented and testing
actions were performed to ensure its functionality. Signal
generation, signal shaping and frequency and amplitude
measurement and display have been verified. Results of each
section have been clarified.
A. Signal generation by hardware component
For the sinusoidal generation the potentiometer (R5) was
adjusted until the oscillation start to grow. It was noticed that
changing the value of the potentiometer caused the resistor
between the two diodes to decrease thus resulting in
destroying the shape of the signal. It was found that the value
that gives the purest shape is 20% from the value of the
potentiometer.
For the triangle and square waves it was noticed that the value
of the potentiometer (R1) affects the shape of the signal adding
some sort of signal distortion. . It was found that when the
potentiometer value was 50% the signal would have the best
shape.
B. Signal generation using microcontroller
The microcontroller circuit was implemented successfully
in laboratory and tested for a wide range of frequencies it was
found to be very accurate.
When all the parts that of the designed multi-function
generator were integrated together, the overall circuit was
implemented successfully and found to work in a good an
accurate way.
The below pictures demonstrate the functionality of the
system
(b)
Figure 3. Displaying the frequency and the amplitude
VII. CONCLUSION
With the completion of this research a multi-function
generator has been successfully designed and implemented
and it has worked as expected. The final design was
successfully implemented and it is found the output frequency
and amplitude of the signal is very stable and can be
controllable from low values to relatively large values, also
the output signal is distortion free. It was noticed that the
signal generator provides very low spurious i.e. noise is
negligible. The amplitude and frequency of output signal can
easily be change over a wide range. The function generator
gives accurate measurements for the amplitude and the
frequency of the signal.
ACKNOWLEDGMENT
The authors would like to thanks Dr.Sharif.F Babikir, DEEE,
UofK for his kind support and motivation. The authors would
also like to thank H.Hamza and Y. Osman, UofK, for their
support of this research work. Finally the authors would like to
thanks all the technicians in EEE department, UofK.
REFERENCES
[1] http://en.wikipedia.org/wiki/Function_generator, accessed on 9 September
2012.
[2]U.A.Bakshi, A.V.Bakshi, K.A.Bakshi, "Electronic Measurement and
Instrumentation", Forth revised edition- 2009.
[3] James Cox, " Fundamental of Linear Electronics: Integrated and Discrete
", second edition-2001.
[4]Adel S.Sedra , University of Waterloo, Kenneth C. Smith, University of
Toronto, " Microelectronic circuits ", 2004.
[5] Paul Horwitz Winfielf Hill " The Art of Electronics " second edition
1989.