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California University of Pennsylvania Department of Applied Engineering & Technology Electrical / Computer Engineering Technology EET 215: Introduction to Instrumentations Lab No.8-( Part 1 of 2) Distance Measurements Using Ultrasonic Sensors. Names: 1. 2. 3. Signature: Date Instrumentation Amplifier Objective of the Experiment The main objective of this experiment is to understand the operation of a basic ultrasonic sensor and the triggering circuitry. Learning Outcomes Students will demonstrate: - The ability to design, construct, and troubleshot astable and a monostable multivibrators. Ability to relate the timing diagram to the basic understanding of the two multivibrators The ability to develop a linear relationship between pulse width and distance measurements The ability to interface to to a DAQ system to display distance measurements. Introduction This experiment I divided into two parts: Part -1 (Today’s experiment) is astable multivibrator circuit Part-2 (next week’s experiment) is the triggering circuit and the ultrasonic transmitter/receiver interface. Triggering Circuit. This circuit is composed of two stages. The astable (free running) multivibrators. This part provides a clock timing to the monostable (one-shot) circuit. A- Astable (Free Running ) multivibrator Source: http://www.electronics-tutorials.ws/waveforms/555_oscillator.html This circuit provides an output according to the following equations: t1 = high time = 0.693(R1+R2)C1 t2 = low time = 0.694 R2C1 T = period = t1+t2 f= 1/T B- Monostable (One-Shot) multivibrator This circuit provides a single pulse once a negative edge trigger is applied to the input(pin-2). The duration of the pulse is determined by the components R1 and C1 as follows: tON = 1.1 R1C1 The negative edge trigger is a result of the signal from the free-running multivibrators and a wave shaping circuit (to be shown later.) Components Needed: - 555 timer - 200KΩ resistor - 47KΩ resistor - 0.1uF cap Experiment Close LABVIEW and turn the power to the board off For better connections and less errors. Connect one of the busses on your breadboard to 5V and the other to GND. A- Build the free-running multivibrator circuit shown: VCC 5V R1 200kΩ 8 VCC R2 47kΩ 4 RST 7 DIS 6 THR 2 TRI 5 CON OUT GND 1 C1 0.1µF 3 BCalculate the anticipated high and low times as follows: t1 = high time = 0.693(R1+R2)C1 t2 = low time = 0.694 R2C1 T = period = t1+t2 f= 1/T thigh (ms) tLow (ms) T (ms) f (Hz) CTurn the breadboard power on and monitor the Timer’s output on Ch0 (use the BNC connector) DLaunch the ELVIS instrument launcher and on the score of Ch0, monitor the output. (The output is on pin 3 of the timer.) You should see a waveform similar to the one below. Ensure that the settings on the scope are correct. (may refer to previous labs if needed.) E- From the Scope, record the high and low times thigh (measured) (ms) tLow (measured) (ms) F- Are the measured and calculated values close ? ----------------------- G- Monostable Multivibrator (One-Shot) and interface circuit (Next Week.) Instructor approval of experiment completion: