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ME302: Mechatronics

Unit 5: Signal Processing   In any mechatronic system, signals flow into and out of the system. These signals are essential for controlling the system and feeding back information about the system. These are effectively the nerve signals in the system. The signals that are received from the physical world and sent to the controller are not in a suitable format. They need to be converted to a suitable format in order to allow the controller to make use of them. This is the aim of signal processing or signal conditioning. Signal processing or signal conditioning in the mechatronics context is the conversion of feedback signals such that they are suitable for use by the controller.

However, these signals require different types of processing. For example, the signal could be mixed with noise; thus, it could be in need of filtering. It could be weak and small in value; thus, it could be in need of amplification. It could be in an analogue format; thus, it could be in need of conversion to a digital format. These are examples of some of the signal processing operations that are required.

This unit will introduce you to the principles of signal processing and the electronic circuits that can achieve such processing.

Unit 5 Time Advisory
This unit should take approximately 6.25 hours to complete.

☐    Subunit 5.1: 1.5 hours

☐    Subunit 5.2: 0.75 hours

☐    Subunit 5.3: 4 hours

Unit5 Learning Outcomes
Upon successful completion of this unit, you will be able to:
- identify types of signal processing that need to be applied to a signal; - explain how to design electronic circuits for amplification, summing, subtraction, comparison, integration, and filtering; - explain the reasons for converting signals from analogue to digital and from digital to analogue; and - identify a type of analogue to digital converter, and explain its principle of operation.

5.1 Operational Amplifier Circuits   An operational amplifier is an electronic circuit building block that can be used to build signal conditioning circuits. It saves the user from the need to re-invent the wheel, such that he or she does not need to build an amplifier circuit but merely needs to connect the operational amplifier such that the function of the circuit is achieved. The operational amplifier is often referred to as op-amp for brevity.

  • Reading: University of Jordan: Dr. Lutfi Al-Sharif’s “Signal Conditioning and Processing” Link: University of Jordan: Dr. Lutfi Al-Sharif’s “Signal Conditioning and Processing” (PDF)

    Instructions: Please click on the link above and read the first five sections of the document on pages 1–11. You will continue reading this text in subunit 5.2.

    Studying these sections should take approximately 1 hour and 30 minutes.

    Terms of Use: This resource is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 license. It is attributed to Dr. Lutfi Al-Sharif and the original can be found here.

5.2 Filtering Circuits   In certain conditions, the signal is contaminated with noise. If the noise has a frequency that is different to the frequency of the signal, then it is possible to remove the noise from the signal by a process known as filtering. Filtering removes components of a signal based on frequency. Filters are one of four types: low pass filtering, high pass filtering, band pass filtering, and bandstop filtering.

  • Reading: University of Jordan: Dr. Lutfi Al-Sharif’s “Signal Conditioning and Processing” Link: University of Jordan: Dr. Lutfi Al-Sharif’s “Signal Conditioning and Processing” (PDF)

    Instructions: Please click on the link above and read section 9 of the document on pages 15–18.

    Reading this section should take approximately 30 minutes.

    Terms of Use: This resource is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 license. It is attributed to Dr. Lutfi Al-Sharif and the original can be found here.

  • Web Media: Colorado State University: Alciatore and Histand’s “Video Demonstrations from Introduction to Mechatronics and Measurement Systems” Link: Colorado State University: Alciatore and Histand’s “Video Demonstrations from Introduction to Mechatronics and Measurement Systems” (Windows Media Player)

    Instructions: Please click on the link above and then watch video number 11.6 titled “Robot Controlled by EMG Biosignal,” noting the different types of signal processing applied. In the robotic arm project shown in this video, notice how the signal extracted from the arm is band stop filtered in order to remove the noise from it. You will realize how important signal processing is in preparing a signal for use by the controller.

    Watching this video and pausing to take notes should take approximately 15 minutes.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.

5.3 Analogue and Digital Signal Conversion   Signals in the physical world exist in an analogue format, whereby the signal magnitude is analogous or proportional to the physical variable magnitude. In order to process a signal within a digital controller or a laptop, it has to be converted to a digital format in which a signal is represented in bits. It is important to convert analogue signals to digital signals and vice versa. These two processes are denoted as analogue to digital conversion (A to D conversion or ADC) and digital to analogue conversion (D to A conversion or DAC).

ADC is necessary to acquire signals from the real world and use them within the controller. DAC is necessary to allow the controller to output a signal to the physical world to control a system.

  • Reading: All About Circuits: Tony R. Kuphaldt’s Volume IV, Digital: “Chapter 13: Digital Analogue Conversion” Link: All About Circuits: Tony R. Kuphaldt’s Volume IV, Digital: “Chapter 13: Digital Analogue Conversion” (HTML or PDF)

    Instructions: Please click on the link above and read “Chapter 13: Analogue Digital Conversion.” You may use the table of contents to read each section of this chapter in HTML format. You may also consider clicking on the PDF link in the upper right hand corner of the page to access the PDF version of the text.

    Reading this chapter should take approximately 4 hours.

    Terms of Use: Please respect the copyright and terms of use displayed on the webpage above.