Lab Eee.doc 2nd

Objectives 1. To construct voltage level detector. 2. To construct an under voltage indicator which gives L.E.D signal

whenever a low voltage is detected compare to reference voltage. 3. To combine voltage level detector and under voltage indicator for

observing their relationship.

A. Voltage Level Detector

Components:

1. IC (Integration circuit) LM741

2. L.E.D (light emitted diode)

×3 ×1 green ×1 yellow ×1 red

3. 330Ω resistor

×3

4. 3.3kΩ resistor

×3

5. 24kΩ resistor

×1

Procedures:

1. The voltage level detector is constructed as shown in the diagram. 2. The voltage level detector is connected to the voltage supply.

3. The diode change due to voltage changes is observed. 4. The changes of the diode is recorded in Table 1. 5. The observation is discussed.

B. Under voltage Indicator Components: 1. 10kΩ resistor

×1

2. 680Ω resistor

×1

3. 4.7kΩ resistor

×1

4. 4.7MΩ resistor 5. 43Ω resistor 6. L.E.D 7. 0.68uF capacitor

×1 ×1 ×1 ×1

8. PN2907 transistor

×1

9. PN2222 transistor

×1

Procedures: + Vref

-

+ Vin

-

1. The circuit shown in diagram is constructed. 2. 3V (around 0.07A) is supplied to Vref. 3. Vin with voltage below 3V and above is supplied, the difference is

observed. 4. Vref with 2V,4V and 5V is supplied. When the LED begin to flash, the

voltage value of Vin is jot down in Table 2.

C. Combination of Voltage Level Detector and Under voltage Indicator Procedures: 1.

Both voltage level detector and under voltage indicator is combined by gathering both Vref of voltage level detector and under voltage indicator while VBat of voltage level detector with Vin of under voltage indicator.

2. Vref with a constant voltage value which is 5V is supplied. 3. The combination of VBat and Vin is supplied with 5V, 4.5V, 4V, 3.5V and

until 0V.

4. The observation is recorded in Table 3.

Results:

Voltage (v) 5.0

Observation Diode Gree Yello Red n w On On On

4.5 < V 5.0 4.5 4.0 < V 4.5 4.0 3.5 < V 4.0 3.5 3.0 < V 3.5 3.0

< < < <

On

On

On

Off

On

On

Off

On

On

Off

Off

On

Off

Off

On

Off

Off

Off

Off

Off

Off

Off

Off

Off

Table 1

Vref (v) 2.0 3.0 4.0 5.0

Vin (v) 0.4 1.4 2.6 3.8

Table 2

Voltage (v) Vref 5.0 5.0

Vin 5.0 4.5 < V <

LED Not flash Flash

Observation Diode Green Yellow On On On On

Red On On

5.0 4.5 4.0 < V < 4.5 4.0 3.5 < V < 4.0 3.5 V < 3.5

5.0 5.0 5.0 5.0 5.0 5.0

Flash

Off

On

On

Flash

Off

On

On

Flash

Off

Off

On

Flash

Off

Off

On

Flash Flash

Off Off

Off Off

Off Off

Table 3

Discussion: 1. Functions of the components which have been used in the experiments; a. Light Emitted Diode (L.E.D.) is use for emitting the light when an electric current passes through it.

b. Integration circuits (IC or chips) are the complex circuits which have been etched on to tiny chips of semiconductor. c. Transistor has the ability to use a small signal applied between a pair of its terminals to control much larger signal at another pair of terminals. It can act either as a switch or as an amplifier. d. Capacitor is a component which capable to store electrical charge for a long time after power has been turned off in a circuit. e. Resistors are used to produce the require constant value of voltage for each part of circuit. 2. The first experiment which construct the voltage level detector, the

resistors are arranged in series and acted as voltage divider. 3. In a series circuit, there is only one path for current between two point, so that, the current is the same for the whole circuit. Since the current is same, the value of voltage is proportional to the value of resistor. 4. In this circuit, the voltage level can be determine when only the specify value of voltage will make the specify L.E.D. off. Thus, the voltage level can be detected. 5. The second experiment which construct the under voltage indicator, the transistors are used to produce the signal for L.E.D. which blink when the value of voltage provided is lower than the reference one. 6. About the capacitor, it stores the charge, therefore, although the value

of voltage is zero, the L.E.D. can still blink for some period. 7. In the combination of voltage level detector with under voltage indicator, it gives the same result as it is alone. The L.E.D. in voltage level detector off one by one due to the value of voltage through it. And in the under voltage indicator, L.E.D. will start blink when the value of voltage lower than reference voltage and it is still blinking although the value of voltage turn to zero. 8. Some cautions need to be considered through the experiments; a. Make sure the components are connected correctly due to its

polarity b. Make sure all the components are correctly connected to each other to avoid the short circuit. c. Make sure the right wires are connected either for positive path or negative path.

d. For the integration circuits, the pin configuration should be correctly determined and connected in the circuit, especially for the positive and negative terminals. Any reverse or wrong connection could damage the component. e. Make sure to connect a resistor in series with the base of the transistor to limit the base current. Otherwise the transistor could be damaged. 9. Both voltage level detector and under voltage indicator are used in

widely range of electrical appliances and electronic devices to give signal or detect for any low voltage happen. 10. Other than that, the application of the circuits can be improved other

than detecting low battery voltage to such as power fail indicator, battery backup control and so on.

Suggestions for further work in the future: 1. Prepare the electrical and electronic components which in good condition. 2. Do not use red maker while writing on the whiteboard because it is unclear. 3. Use LCD projector to show how to do the experiment. 4. Use microphone to give the explanation.

Conclusions: 1. The voltage level detector was constructed. 2. The under voltage indicator was constructed and gave the L.E.D signal whenever a low voltage was detected compare to reference voltage. 3. The voltage level detector and under voltage indicator were combined and their relationship were observed.

References:

1. J. David Irwin, Basic Engineering Circuit Analysis, (7th Edition), John Wiley and Sons Inc,2002 2. David E. Johnson, John L. Hilburn, Johnny R. Johnson, Peter D. Scott, Basic Electric Circuit Analysis, (5th Edition), Prentice Hall, 1995 3. Robert J. Herrick, DC/AC Circuits and Electronics: Principles & Applications, Theorem Delwan Learning, New York, 2003 4. Thomas L. Floyd, Principles Of Electric Circuits: Electron Flow Version, (3rd Edition), Macmillan Publishing Company, New York, 1993 5. Thomas L. Floyd, Principles Of Electric Circuits: Conventional Current Versions, (8th Edition), Pearson Prentice Hall, New Jersey, 2007