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ACTIVITY 1

Pressure sensor 

Electrical diagrams

Fig. 3.1 - Pressure

Fig. 3.2 - Instrumentation Amplifier  

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Topographical diagram

Fig. 3.3 

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Obtained results

Position of the syringe Sensor Output Voltage

[V] 

3 

2.5 

2 

1.5 

3.5 

4 

4.5 

Tab. 3.1 

EXPERIMENTATION

The circuit that will be used is the one in Figure 3.1 that represent the function that is performed

 by the PRESSURE block.

Pressure sensors contain sensing elements that consist of four piezoresistors buried in the face of

a thin, chemically-etched silicon diaphragm. A pressure change causes the diaphragm to flex,

inducing a stress or strain in the diaphragm and the buried resistors. The resistor values change in proportion to the stress applied and produce an electrical output.

In consideration of the very low output voltage of the bridge it is necessary to use the amplifier of

the INSTRUMENTATION AMPLIFIER block. This amplifier is of the "instrumentation" type,

that is, it has impedances that are very high and equal at both inputs (inverting and non inverting),

low offset voltage and low bias current. Therefore, it is suitable for those cases where it is

necessary to operate with very low voltages.

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Furthermore, the amplifier of the INSTRUMENTATION AMPLIFIER block has the

characteristic of having the gain that can be determined through the position of the dip switches:

the gain can assume the values 1, 10, 100, 1000.

N.B: The Wheatstone bridge of the pressure sensor should not be supplied from the outside, it's

supplied by the reference voltage of 5 volts.

The terminals serve only to take measurements of voltage and current.

1) Insert the Module DL 3155E25T in the console and set the main switch to ON;

2) Connect, through two leads, the terminal 4 to the terminal of the inverting input and the

terminal 2 to the terminal of the non inverting input of the INSTRUMENTATIONAMPLIFIER;

3) Move the piston of the syringe to the initial value of 3ml;

4) Insert the multimeter, set for the measurement of direct voltages, between the terminal Vo

of the INSTRUMENTATION AMPLIFIER block and the earth and measure the voltage;

5) Set the gain of the amplifier to max value (1000), eventually if the output voltage is to high

(over 13V) decrease the gain;

6) Write the measurement that you have, i.e the read on the multimeter divided by the gain;

7) Move the piston to next position as wrote in Table 3.1;

8) Write the measurement that you have calculated in Table 3.1;

9) Repeat such measurement for all the positions that are listed in the table;

10) Comment the behavior of the measured voltage as a function of the position of the syringe

(piston).

ACTIVITY 2

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P.I.R. sensor 

Electrical diagram

Fig. 4.1

Components List

P.I.R. sensor with Fresnel lens

Transistor: BC337

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Red LED

LED's Resistor: 470Ω

Transistor's resistor: 4.7kΩ

Topographical diagram

Fig. 4.2 

EXPERIMENTATION

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1) Insert the Module DL 3155E25T in the console and set the main switch to ON;

2) Connect a multimeter, set as voltmeter, as show in Fig. 4.2;

3) Wait few seconds (the sensor will be warmed up);

4) Now when the sensor will see a movement the led starts flashing, until the movement will

stop;

5) Move far from the sensor to check the range (usually some meters);

6) Comment the obtained results.

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ACTIVITY 3

Magnetic switch - Reed sensor 

Electrical diagram

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Fig. 5.1

Components List

Reed switch

Reed magnet

E = red lamp

R = 470Ω

Topographical diagram

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Fig. 5.2 

EXPERIMENTATION

1) Insert the Module DL 3155E25T in the console and set the main switch to ON;

2) Connect a multimeter, set as voltmeter, between jack 1 and ground (Fig. 5.2);

3) Adjust the input voltage +V so to read on the voltmeter a voltage of 10V;

4) Bring near the magnet slowly to the switch S1, so to provoke the contact closing and the

consequent switching on of the lamp;

5) Remove slowly the magnet so to provoke the contact opening and the consequent switching

off of the lamp;

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6) Repeat more times the previous operations, by spotting the minimum closing distance of the

switch;

7) Comment the obtained results.

ACTIVITY 4

Hall sensor 

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Electrical diagram

Fig. 6.1

Components List

Hall sensor SS495A

Transistor: BC337

Red LED

LED's Resistor: 470Ω

Transistor's resistor: 4.7kΩ

Topographical diagram

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Fig. 6.2 

EXPERIMENTATION

The sensor have a ratiometric output voltage, set by the supply voltage. It varies in proportion to

the strength of the magnetic field.

1) Insert the Module DL 3155E25T in the console and set the main switch to ON;

2) Connect a multimeter, set as voltmeter, as show in Fig. 6.2;

3) Approach slowly the magnet to the sensor, so to provoke the sensing. The effect is also

identifiable by a light changing of the led;

4) Remove slowly the magnet;

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5) Turn the magnet of 180°, to change the polarization of the magnet, and repeat the last two

steps;

6) Comment the obtained results.

QUESTIONS:

1. Discuss how an infrared sensor performs motion sensing.

2. What is the importance of the instrumentation amplifier in detecting the applied pressure

on the piston?

3. Using the concepts acquired in this experiment, design a simple circuit where a P.I.R.sensor is used to make a security alarm and sense movement onto its surrounding.