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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 32. L.E.D (light emitted diode) 1 green

1 yellow

1 red3. 330 resistor 34. 3.3k resistor 35. 24k 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.

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B. Under voltage Indicator

Components:

1. 10k resistor 12. 680 resistor 1

3. 4.7k resistor 1

4. 4.7M resistor 1

5. 43 resistor 1

6. L.E.D 1

7. 0.68uF capacitor 1

8. PN2907 transistor 1

9. PN2222 transistor 1

Procedures:

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. Vrefwith 2V,4V and 5V is supplied. When the LED begin to flash, the

voltage value of Vin is jot down in Table 2.

+ Vref

-

+ Vin

-

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C. Combination of Voltage Level Detector and Under voltage Indicator

Procedures:

1. Both voltage level detector and under voltage indicator is combined bygathering both Vrefof voltage level detector and under voltage

indicator while VBat of voltage level detector with Vin of under voltage

indicator.

2. Vrefwith 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.

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Results:

Voltage

(v)

ObservationDiodeGree

n

Yello

wRed

5.0 On On On4.5 < V