ENGG 1015 THE UNIVERSITY OF HONG KONG Lab#3 Hayden K. H. So 1st Semester 10/11 Kenneth K. Y. Wong INTRODUCTION TO ELECTRICAL & ELECTRONIC ENGINEERING

LABORATORY #3 DEMONSTRATION: A FLAVOR OF THE FINAL PROJECT In this demonstration, you will get a flavor of a sample stage which combines sensor, relay, and load as shown in Fig. 1(a) [15 mins].

Fig. 1(a)

EXERCISE: CIRCUIT WITH VARIOUS SENSORS In this exercise, you will build on top of the results from Exercise 2 of Lab#2 to construct a slightly more complex circuit. Instead of using a variable resistor (VR) to turn on/off the device, we will explore different input stages. Furthermore, a solid-state relay (SS-RELAY) is still used to isolate the input stage (VR) with the driving stage (e.g. fan, motor, etc.).

Fig. 1(b)

To give you a better idea, Fig. 1(b) shows a photo of the sample final product with a fan as the driving stage on the right and a reed switch on the left to switch on a light bulb. You will work on ALL kinds of sensors as following: 1) reed switch; 2) linear position sensor; 3) sound impact sensor; 4) QTI optical sensor.

Magnectic Reed Switch (Normal Opened (N.O.) / Normal Closed (N.C.))

Fig. 2 (a)

Fig. 2 (b)

A magnetic reed switch operates in similar ways to the mechanical switch you have experimented with from Lab 2, except that a magnetic reed switch is controlled by a magnet. Fig. 2(a) and (b) shows two ways you may utilize a magnetic reed switch to control the output lamp by connecting to either the normal opened (N.O) or the normal close (N.C.) terminal respectively. Now, construct the circuit so that it can control the light bulb and determine the approximate distance of the magnet from the switch that will turn on/off the lamp [10 mins].

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Linear Position Sensor

Fig. 3

Fig. 3 shows a circuit utilizing a Linear Position Sensor acting as an input stage on the left. A linear position sensor operates similarly to the (rotary) VR in Lab 2 except that the resistance is linearly proportional to the position of the metal bar. Now, construct the circuit so that it can control the light bulb by pressing/depressing the metal bar. Note that by interchanging the connection between the yellow and green wire, the operation will be reversed. 1. Start with the 1st configuration in this exercise, with yellow connected to Vcc, and green

connected to GND. Does the lamp turn on or turn off when the metal bar is pressed? Without performing any measurement, can you guess if the resistance between the red and green terminal increases or decreases when the metal bar is pressed inward? [15 mins].

2. Now, reverse the yellow and green connections, verify the operation of your circuit has reversed also. [5 mins]

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Sound Impact Sensor

Fig. 4

Fig. 4 shows the circuit with the Sound Impact Sensor on the left. It provides a means to add noise control to your project and responds to loud noises such as a clap of the hands. Through the on-board microphone, this sensor detects changes in sound level, which triggers a high voltage pulse to be sent through the signal pin of the sensor. Now, construct the circuit so that it can control the light bulb. 1. Turns on/off the lamp by making some noise. What is the approximate maximum

distance that your circuit can still operate? [15mins] 2. Now, adjust the value of the on-board trimmer (a variable resistor) to adjust the

sensitivity of the sensor. Does the sensitivity increase or decrease when the trimmer is turned clockwise? [5 mins].

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QTI Optical Sensor

Fig. 5

black

Vcc

Rir

red

white

QTI sensor Fig. 6

Fig. 5 shows the circuit with the QTI Optical Sensor on the left. It contains an infrared (IR) reflective sensor to determine the reflectivity of the surface below it. When the QTI sensor is over a dark surface, the reflectivity is very low; when the QTI is over a light surface, the reflectivity is very high and will cause a different reading from the sensor. The black box, in effect, behaves like an IR controlled resistance (Fig. 6).

1. Now, construct the circuit in Fig. 5. Place a white reflector about 5cm from the sensor. Does the lamp turn on or off? What if you put it at around 1cm? Estimate the approximate distance needed to turn on the lamp using a white reflector.

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2. Replace the white reflector by reflectors with different grey scale (20%, 40%, 60%, 80%) and color (R/G/B/C/Y/M). Which color/grey level reflector is best at turnning on the lamp? Can you explain why?

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