Lab4Spring2010 - ECE 25 Introduction Lab 4 Sequential...

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ECE 25 Lab 4 Se Introduction Goal: Design a circuit to recogni will then be used in Lab 5 to desi register. Information on the IR S read over lightly up to Page 4. Y state diagram for a sequence reco When you press a button on the S at the TV looks like on a scope a removed. (The modulation is use equential Circuits, Sequence Recognize ize the start bit and data bits for a Sony IR remot sign a circuit to load the code from the remote in SONY protocol can be found on Lab Web site. T ou should also read Example 6.2 in the book wh ognizer. SONY remote, the trace shown above is what th after the high frequency modulation at ~ 40 kHz ed to reject background light.) Starting from the er te. This logic nto a shift This should be hich describes the he received signal has been left of the figure,
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ECE 25 Lab 4 2 there is the start bit, which is approximately 2.4 milliseconds long. This start bit tells the receiver that there is a block information after it. Then there is a fixed delay of about 0.6 ms and then a “1” bit of approximately 1.2 ms long. This is followed by another fixed delay of ~0.6 ms and a “0” bit which is about .6 ms long. This type of waveform encodes the “1” and “0” logic states using the width of a fixed amplitude pulse instead of the amplitude of a fixed width pulse as we have done earlier. This encoding technique is called Pulse Width Modulation (PWM) with the logic values represented by timing information (pulse widths) instead of the amplitude of fixed width pulses. (For more information, refer to the Sony Remote Datasheet.) After the start bit, the next seven bits are the control code, the following bit is a separator, and the last four bits are the device code. We will always use TV which is 0000. The number of bits for the device code varies depending on the device. For TVs, there are seven control bits after the device code for a total of 12 (4 for the device, 7 for control.) If a DVD player was being controlled, there would be 15 control bits. Therefore, always be sure that the remote is set to operate a TV and not another device. We want to build a sequence recognizer that recognizes the start bit, a “0” bit, or a “1” bit. To do this, we need to transform the analog waveform out of the IR remote into a sequence of bits. This is accomplished by applying the signal to an input of a sequential circuit, and then clocking (sampling) the circuit at a known rate. For our circuit, we will clock the incoming waveform at 3.9 kHz or .256 milliseconds. A start bit with a length of 2.4 ms. The total number of clock cycles if the edge of the clock is aligned with the start bit will be 2.4/0.256 =9.3 cycles. The start bit will then produce a sequence of a “1” followed by either 9 or 10 “0”s and then another “1”. The reason we cannot be sure if either 9 or 10 “0”s is produced is because the rising edge of the start signal from the remote and
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Lab4Spring2010 - ECE 25 Introduction Lab 4 Sequential...

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