Contents

1. Aim Page 3
2. Equipment Page 4
3. Circuit Diagrams Page 6
4. Method/Procedure Page 7
4. Conclusion Page 9

Aim

For this assignment I aim to accomplish a better understanding of an RC filter (Resistor Capacitor) which is a circuit that comprises of at least one capacitor and resistor and the circuit must also be driven by a voltage or current source. Understanding this will enable me to demonstrate my knowledge based on this report about Resistor Capacitor Filters.
Equipment

For the experiment, we were provided with five different types of equipment. The electronic equipment that we used was indeed very essential in order to carry out the experiment. The following equipment that was used in this experiment is as follows:

Resistance Decade Box – Is a variable resistor used for limiting the amount of current that flows within the circuit.

Capacitor – Is an electronic device that serves an important role within electronics. It functions by collecting and storing electricity. Capacitors are made up of 2 equally charged conducting surfaces having opposite signs and separated by a dielectric which is the insulator.

Signal Generator – Also known as a function generator is an electrical hardware device that allows the user to adjust frequency, output voltage, impedance, waveform, and modulation. In this experiment we are using the signal generator in conjunction with the oscilloscope.

Oscilloscope – An oscilloscope is an electrical hardware device that measures voltage and frequency.

Four wires and 2 cable connector wires – To connect to the resistance decade box, signal generator and oscilloscope.

(The equipment list is visually represented in the images below)

Circuit Diagrams

The 2 circuit diagrams below illustrate how my group and I set up the equipment mentioned above.

Low Pass Filter

[pic]

High Pass Filter

[pic]

Method/Procedure

As you can see from the circuit diagrams illustrated above that was how we set up the circuit using the equipment provided.

➢ Low Pass Filter Circuit

In the first circuit we connected the oscilloscope and the signal generator together using the 2 cables. We then connected the rest of the circuit using the four wires so that the resistance decade box was set in series whilst the capacitor is set parallel which is an essential set up for a low pass filter circuit.

➢ High Pass Filter Circuit

In the second circuit again we connected the oscilloscope and the signal generator together using the 2 cables. We then connected the rest of the circuit using the four wires however this time the resistance decade box and capacitor have switched places meaning that the capacitor was connected in series whilst the resistance decade box is set parallel making this circuit a high pass filter.

In both of the circuits we set the resistance decade box to a resistance of 1 kilohms and the capacitor to 0.1 microfarads. This was done on both circuits in order to maintain a fair experiment with the only difference being that circuit 1 was a low pass filter and circuit 2 was a high pass filter.

For each circuit we introduced the same amount of frequency. There were 10 different frequencies starting from 100 Hertz and ending at 20 Kilohertz. Although we had changed the frequency after each result we had kept the voltage the same at 1 volt. Using the oscilloscope as a visual representation we measured and recorded the voltage that came out.

Results

|Circuit 1 | | | | |
|Frequency, Hz |Voltage in |Voltage out |Gain |Decibel Gain (dB) = |
| |= Vin |= Vout |= Vout/Vin |20log10 Vout / Vin |
|100 Hz |1 |1 |1 |0 |
|200 Hz |1 |1 |1 |0 |
|400 Hz |1 |1 |1 |0 |
|1 kHz |1 |0.8 |0.8 |-1.9 |
|1.5 kHz |1 |0.7 |0.7 |-3.1 |
|2 kHz |1 |0.6 |0.6 |-4.4 |
|4 kHz |1 |0.36 |0.36 |-8.9 |
|10 kHz |1 |0.16 |0.16 |-16 |
|15 kHz |1 |0.12 |0.12 |-18.4 |
|20 kHz |1 |0.07 |0.07 |-23.1 |
| | | | | |
|Circuit 2 | | | | |
|100 Hz |1 |0.6 |0.6 |-4.4 |
|200 Hz |1 |0.8 |0.8 |-1.9 |
|400 Hz |1 |0.9 |0.9 |0.9 |
|1 kHz |1 |0.9 |0.9 |0 |
|1.5 kHz |1 |1 |1 |0 |
|2 kHz |1 |1 |1 |0 |
|4 kHz |1 |1 |1 |0 |
|10 kHz |1 |1 |1 |0 |
|15 kHz |1 |1 |1 |0 |
|20 kHz |1 |1 |1 |0 |
Conclusion

From the graphs shown, the relationships of the circuits seem to behave in an almost opposite way. Circuit 1 stays at 1 voltage out as well as gain during the first 3 low frequency tests meaning that it does not respond allowing low frequencies to be filtered. However when a higher frequency rate is introduced starting from 1 kilohertz we start to see a change going from 1 to 0.8. For the subsequent 2 outcomes we continued to increase the frequency by 500 Hertz at a time and noticed that the results for voltage out and gain were decreased to 0.7 then 0.6. We deduced that as the frequency increased by 500 Hertz, the voltage out and gain will decrease consecutively by 0.1 respectively.

The graph for Circuit 2 shows that during the first 4 tests the voltage out and gain are responding to the low frequencies as they increased from 100 Hertz to 1 kilohertz. The results show an almost consecutive manner of increasing. From 1.5 kilohertz onwards the graph shows that the high pass filter does not respond to any increases in frequency meaning that it has filtered out the high frequencies.

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Michael Luong

2010

Multimedia Technology
Laboratory Report – RC Filters
Jerry Foss

Resistance Decade Box

Capacitor

2 cables

Four different coloured wires

Signal Generator

Oscilloscope

Resistance Decade Box

Capacitor

Wire Connectors

Capacitor

Resistor Box

Wire Connectors