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Unformatted text preview: 2.737 Mechatronics Laboratory Assignment 3: Digital Electronics: An Encoder Interface Assigned: Session 13 Reports due: Session 18 in checkoffs Reading: Horowitz and Hill, Ch. 8; accompanying data sheets Prelab exercises: The prelab is due in class on Wednesday , Session 16. For the prelab: 1. Understand the operation of the encoder and the circuit. Sketch the requested wave- forms as the encoder is rotated clockwise and counter-clockwise. 2. Provide us with a schematic of the circuit with the pin numbers assigned, and explain how you assigned these. Be sure to include a schematic of your debounce circuit. 3. Build and test your debounce circuit. Include scope data showing that it operates properly. 4. Understand the operation of the commercial encoder interface chip and answer all of the questions in that section of the lab. Include sketches of relevant waveforms. How is this commercial device better or worse than the circuit you will build? What are the fundamental differences in operation? What about noise immunity? 1 Introduction The purpose of this lab is to teach you how to build, understand, and design digital elec- tronics. To this end, you will fabricate a circuit to interface with a rotary encoder. In the process you will also learn about how encoders work. These are an important class of sensors in mechatronic systems. In order to expedite the lab effort, you are given the circuit for the system. The circuits are to be built individually on your protoboard and demonstrated in the checkoff. The parts you need for this exercise are available in the lab. 2 Preparation Before going into the lab, please take the time to understand how the circuit works. You will find the schematic diagram at the back of this handout. As part of the lab we have also supplied you with data sheets for all of the components. Take a look through these in order to learn how each of the components functions. We have also supplied you with the data sheet for a Hewlett-Packard integrated circuit which implements an encoder interface and provides ready interfacing with a microprocessor. Commercial systems would likely use such a chip. One section of the lab asks you questions about this chip. 1 1. First understand how an encoder works. To this end, the class lecture on encoders will be very helpful. Please also refer to the data sheet for the Bourns encoder used in the lab. 2. Look at the circuit and be sure you understand its operation. Sketch some expected waveforms through the circuit as the encoder is rotated through several states clock- wise, and then through several states counter-clockwise. 3. Note that we have not assigned pin numbers to the logic elements. Read through the individual chip data sheets and use this information to assign pin numbers to all the elements in the schematic. You will need this information before you can wire the circuit. In the checkoff, we will ask you to show us waveforms in various parts of the circuit and to explain these waveforms to us. Thus you will need a copy of the the circuit and to explain these waveforms to us....
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- Spring '99