Bounce Trigger - Jared Tucker Instructor: Dr. Santi ELCT...

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Jared Tucker ELCT 301 Page 1 of 5 Instructor: Dr. Santi 5/13/2009 Subject: Technical Memorandum: Demonstration of a RC-Schmitt network as an effective debouncer and limitations of the LM741 op-amp. The two motives of this lab were to investigate the properties of a debouncer circuit and to test the limitations of an op- amp. The debouncer in this lab consisted of two parts- an RC filter circuit and a Schmitt trigger. The circuit is shown in Figure 1 of the Appendix. The purpose of the Debouncer circuit is to clear out high frequency noise common to analogue switches. If there is too much noise in a system, the chips (comparator networks) have a difficult time differentiating between valid high and low signals. Through observation of the input and output signals at various points throughout the circuit, the necessity of a debouncer was demonstrated in the prelab Figure 2 from the Appendix. The signals at Nodes A, B and C are all equivalent Figure 2. Based on this observation it was obvious that the hysteresis region of the Schmitt trigger was not even being used. It is here necessary to define the upper trigger point (UTP) and lower trigger point (LTP) as the voltage necessary to cause the Schmitt trigger to transition from high to low or from low to high. Figure 3 of the Appendix demonstrates just this effect. The region between the UTP and LTP is known as the hysteresis region. So, the design goal was to decrease the magnitude of the high frequency so it would fall within the hysteresis region of the Schmitt trigger. This way, the Schmitt trigger would transition only when the switch response reached its low (or high) steady state. By using and RC filter summarized in Figure 4 of the Appendix, it was
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This note was uploaded on 04/28/2008 for the course EE ELCT 301 taught by Professor Santi during the Spring '08 term at University of South Carolina Beaufort.

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Bounce Trigger - Jared Tucker Instructor: Dr. Santi ELCT...

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