EECS 100 Timers and Oscillators B Boser L Chua University of California Berkeley Department of Electrical Engineering and Computer Sciences EECS 100 Professor Bernhard Boser Professor Leon O Chua LABORATORY 6 v2 TIMERS AND OSCILLATORS 1 Timers Inductors and capacitors add a host of new circuit possibilities that depend on their ability to remember i e to store energy and thereby signals and information In this laboratory we will look at simple circuits that use capacitors and inductors timers These circuits have many uses Applications include circuits that automatically turn off lights or equipment after a specified period annoying flashers that make lights blink or synthesizers used in sirens or electronic organs Timers are also used by other electronic circuits for example as computer clocks In fact the 555 timer circuit used in this laboratory is one of the most successful ICs ever Designed 1970 by Hans Camenzind at Signetics later Philips and now NXP and introduced 1971 the same year Intel introduced its first 4 Bit microprocessor executing up to 60 000 instructions per second sales are still strong with over 1 billion units sold each year Tell me if you can think of other people who invented something single handedly with similar success and longevity That Intel microprocessor has long been relegated to museums The notorious RC charging and discharging circuit that is at the basis of so many homework and exam problems is also at the center of many timer circuits exams are practical after all For example the time it takes to charge a capacitor to say the supply voltage can be used to delay turning on a device Likewise discharging a capacitor from VCC to VCC sets the time to turn a device off Combine these two circuits and you have a clock turning on and off at a rate set by a capacitor and resistors Turing this simple idea into a complete electronic circuit calls for several functions in addition to the capacitor and charging and discharging resistors Switches are used to alter between charging and discharging cycles Comparators determine when a certain voltage level has been reached Altogether quite a few components are needed to build that timer circuit The 555 timer includes all these functions in an 8 pin package The circuit diagram of the 555 is reproduced below Page 1 EECS 100 Timers and Oscillators B Boser L Chua Since you have not studied capacitors and inductors in lecture yet you will be responsible for just building two simple circuits in this lab The first circuit is the above mentioned 555 timer circuit The fact that you simply apply power to the chip to get a square wave output should be fascinating T 2 Oscillators Negative Resistance Concepts In the previous section you saw how a timer chip can be used to build a square wave generator An analogous approach is to use a negative resistor You will use an op amp to realize the negative resistor in this part of the lab The actual details of building the oscillator will again be revisited later in lecture after you learn about inductors and capacitors The circuit in the black box below realizes a negative resistor or Negative Impedance Converter NIC You can see that the op amp can be considered as a two terminal one port device Page 2 EECS 100 Timers and Oscillators Page 3 B Boser L Chua EECS 100 Timers and Oscillators B Boser L Chua LAB REPORT Lab Session Name 1 SID Name 2 SID 1 Timers 1 Perform a transient analysis in Multisim to verify your square wave output Turn in a copy a plot showing Vout V1 and V2 as a function of time Note that Multisim has a built in component for the 555 timer Multisim output of 10 P 2 Now build the timer circuit in the laboratory Power it from a 5V supply and check the waveforms with the oscilloscope Explain discrepancies with the simulation Comparison of circuit with simulation of 3 M 3 Derive the i v characteristic of the op amp negative impedance converter Show your work below of 10 P Page 4 EECS 100 Timers and Oscillators Page 5 B Boser L Chua EECS 100 Timers and Oscillators B Boser L Chua 4 Simulate the op amp negative impedance converter using MultiSim Using the Agilent Multimer and a DC source in MultiSim fill in the table of values in the lab section of this report of 10 P 5 Build the circuit in lab Use the 6 V supply and the Agilent Multimeter to fill the table of values in the lab section of this report Compare these values to the i v graph obtained from hand calculations and the i v from MultiSim Explain any discrepancies of 10 M Page 6 EECS 100 Timers and Oscillators B Boser L Chua PRELAB SUMMARY Lab Session Name 1 SID Name 2 SID Summarize your prelab P results here and turn this in at the beginning of the lab session 1 Attach MultiSim output of 555 timer functionality Show V1 V2 and Vout 2 Sketch the i v characteristic of the op amp negative impedance converter below i mA v volts Page 7 EECS 100 Timers and Oscillators B Boser L Chua 3 Fill in the table below using the results from your MultiSim simulation v volts i mA 5 2 5 4 3 2 5 1 5 0 5 0 0 5 1 5 2 5 3 4 5 5 2 Page 8 EECS 100 Timers and Oscillators B Boser L Chua SUGGESTIONS AND FEEDBACK Time for completing prelab Time for completing lab Please explain difficulties you had and suggestions for improving this laboratory Be specific e g refer to paragraphs or figures in the write up Explain what experiments should be added modified how or dropped Page 9
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