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EEE1006/1007 Electrical Engineering Project

Electronic Amplifier for Motor Control

Chan Tung Yin Daryl


Stage 1 Marine Technology


This lab report aims to cover and discover the effects of various factors that could potentially alter the performance of an amplifier. To do this, a circuit that was constructed from scratch, was subjected to multiple tests with an expected gain ratio of 9.2. In addition, external equipment such as an oscilloscope, a digital multimeter, a DC power supply and an arbitrary waveform generator were used. The test conducted focus on the performance of the amplifier circuit under different loading conditions and the results of each test will be discussed in this report.


An amplifier is an electronic device that increase the voltage, current or power of a signal[1]. For example in an acoustic system, audio amplifiers consist of  small and large signal amplification stages that supplies power to a driven loud speaker and can produce an amplified signal from 30Hz to 15,000HZ[2].

The gain, denoted as “A”, is the ratio between the input and output magnitude and can be calculated using the formula:

A=V_out/V_in =1+R2/R3


Finding factors that may affect amplifier performance.

Assemble and perform test an amplifier circuit with a theoretical gain of 9.2.

Using a loudspeaker, observe the effects on the frequency when various magnitude of voltage is applied to the circuit

Test the amplifier circuit with a DC motor and observe the behavior and characteristics of the motor when different settings in voltage and resistance are applied.

Testing Procedures

Assembling the circuit

During the first part of the experiment, an amplifier circuit was built, according to the schematic, by soldering loose components onto a circuit board.

Test using sinewaves

The arbitrary waveform generator (ARB) was set to produce a peak-to-peak value of 0.5V and 1kHz of frequency. After which, the ARB was connected to testing point (TP) 2 and testing point 3 on the circuit. The oscilloscope was connected at TP4 and TP5 and the sine graph produced was captured.

Testing using squarewaves

For this test, the process would be similar to the test using the sinewave. The only difference between this test and the sinewave test is that the graph would be different due to the characteristic of the wave applied to the circuit.

Testing using a loudspeaker

In this test, the peak-to-peak value was reduced to a minimum of 20mV using the sinewave. The loudspeaker was then connected to the output amplifier circuit. Next, the voltage was increased gradually until a faint sound could be heard. As the voltage increased, the sound grew from a low pitch hum to a high pitch ring and finally, to a point where no sound could be heard. The frequencies where the faint hum to the silence after the high pitch ring were recorded.

Testing using a DC motor

The ARB was removed and the DC power supply was connected to TP4 and TP5 via the 6V output ensuring that the voltage was set to 0V and the output was switched off. In addition, the digital multimeter was connected to circuit to measure the voltage from the generator. The voltage was slowly increased and the change in behavior of the motor was recorded. Subsequently, swapping the wires reversed the polarity of the voltage and the change in behavior was recorded. Next, to observe the effects on the motor speed during loading, a 10Ω resister was placed across the generator terminals with an input voltage of 0.3V. Finally, the ARB is reconnected to the amplifier at TP1 and TP3 and the resistor removed. The ARB was set to produce a squarewave output of 05.Hz and 0.5V peak and the graph produced on the oscilloscope was recorded.

Calculations and Results

During the construction of the circuit, a suitable value of R2 had to be calculated to produce a gain of 9.2. This was done by using the above formula :

A=V_out/V_in =1+R2/R3

From this equation, the following can be written as:




Next, the value of R4 and R5 can be calculated using ohm’s law.


The current passing through R4 and R5 is measured at 8mA and the voltage across the diodes is 0.7V thus,

R4=R5=14.3V/(8×〖10〗^(-3) )=1787.5Ω

Results from sinewave test

Figure 1. Sinewave as shown on the oscilloscope.

Using the values from the graph above, we can find the gain ratio of the amplifier,

A=4.7/(510×〖10〗^(-3) )=9.22

Results from squarewave test

Figure 2. Squarewave as shown on the oscilloscope.

Using the values from the graph above, we can find the gain ratio of the amplifier,

A=4.9/(530×〖10〗^(-3) )=9.25

In addition, by using Multisim, it is possible to calculate another theoretical gain ratio to check against the experimental values.

Figure 3. Oscilloscope taken from Multisim.

From Figure 3, Channel A represents the input while Channel B represents the output thus giving a theoretical gain:

Using the values from the graph above, we can find the gain ratio of the amplifier,

A=(837.206×〖10〗^(-3))/(91.218×〖10〗^(-3) )=9.17

Results of loudspeaker test

The lowest frequency that could be heard was 1kHz and the maximum frequency was 16kHz-17kHz. A significant difference that could be heard between a sinewave input and a squarewave input is the pitch and clarity of the sound. When using a sinewave input, the sound produced was smoother and more compressed as compared to the squarewave that produced a clearer and higher pitch sound.

Results of DC motor test

Discussion and Future Improvements



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