Lab 5 - 2B 2010

Lab 5 - 2B 2010 - ECE 2B Lab #5 Lab 5 Timers and...

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1 © Bob York ECE 2B Lab #5 Lab 5 Timers and Oscillators Overview This lab continues our exploration of basic transistor switching circuits to include timing circuits and oscillators. We will explore some simple multivibrator circuits using discrete transistors, comparators, and finally circuits that use the popular 555 timer chip. We will use the latter to create a simple fan speed controller using a variable duty-cycle driver. Table of Contents Pre-lab Preparation 2 Before Coming to the Lab 2 Parts List 2 Duty Cycle 3 In-Lab Procedure 4 5.1 Discrete Multivibrator Circuits 4 Manual One-Shot Timer 4 Bistable-Multivibrator or “Flip-Flop” 5 Another Monostable-Multivibrator or “One-Shot” 5 Optional: BJT-based Astable Multivibrator 6 5.2 Relaxation Oscillator with Variable Duty Cycle 7 Schmitt Trigger 7 Relaxation Oscillator Circuit 8 Variable Duty-Cycle Oscillator 9 5.3 The 555 Timer IC 10 Astable Multivibrator 10 Linear Ramp Generator 11 Fan/Motor Speed Control 11 Extra Credit: Self-Contained DC-DC Boost converter system 12
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2 Timers and Oscillators © Bob York 2 Pre-lab Preparation Before Coming to the Lab Read through the lab experiment to familiarize yourself with the components and assembly sequence. Before coming to the lab, each group should obtain a parts kit from the ECE Shop. Parts List The ECE2 lab is stocked with resistors so do not be alarmed if you kits does not include the resistors listed below. Some of these parts may also have been provided in an earlier kit. Laboratory #5 Timers and Oscillators Qty Description 1 2N7000 NMOS 4 2N3904 NPN BJT 1 2N3906 PNP BJT 2 LM393 Comparator 2 LM555CM 4 LED, Red diffused, 5mm (T1 3/4) 20mA 4 0.1uF capacitor (low-volt. ceramic) 4 10uF capacitor (electrolytic, 25V, radial) 2 100uF capacitor (electrolytic, 25V, radial) 8 330-Ohm 1/4 Watt resistor 4 1-KOhm 1/4 Watt resistor 2 2.2-KOhm 1/4 Watt resistor 3 4.7-KOhm 1/4 Watt resistor 6 10-KOhm 1/4 Watt resistor 2 22-KOhm 1/4 Watt resistor 3 33-KOhm 1/4 Watt resistor 8 100-KOhm 1/4 Watt resistor 4 PC Mount Tactile push-buitton switch (PB1) 2 10k trimpot
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3 © Bob York 3 Background information Suggested background reading: Hands-on Electronics, Chapter 9 http://en.wikipedia.org/wiki/Multivibrator Phillips Application Note AN170, “NE555 and NE556 Applications” (posted on course web site). Duty Cycle In this lab we will work with rectangular pulse waveforms, for which the term “duty cycle” comes up frequently. For such waveforms, the duty cycle is defined as the ratio of pulse duration to pulse period. For example, consider the waveform shown in Figure 5-1: Figure 5-1 – Rectangular waveform for duty cycle definition The pulse duration is ; this is how long the pulse remains high (amplitude=1 in the figure).The pulse period is T ; this is the duration of one complete cycle, and is just the inverse of the frequency in Hz ( 1/ f T ). So the duty cycle in this case would be D T (5.1) Clearly 01 D  , which we usually express as a percentage. So, for example, a 50% duty cycle is one where 0.5 D , or 0.5 T .
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4 Timers and Oscillators
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This note was uploaded on 03/17/2010 for the course ECE 2B taught by Professor York during the Winter '07 term at UCSB.

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Lab 5 - 2B 2010 - ECE 2B Lab #5 Lab 5 Timers and...

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