Objectives

Objectives 1. To construct voltage level detector. 2. To construct an undervoltage indicator which gives L.E.D signal whenever a low voltage is detected compare to reference voltage. 3. To combine voltage level detector and undervoltage indicator for observing their relationship. A. Voltage Level Detector Components: 1. IC (Intergrationcircuit) LM741 2. L.E.D (light emitted diode) 3. 330Ω resistor 4. 3.3kΩ resistor 5. 24kΩ resistor

×3 ×1 green ×1 yellow ×1 red ×3 ×3 ×1

Procedures:

1. 2. 3. 4. 5.

The The The The The

voltage level detector is constructed as shown in the diagram. voltage level detector is connected to the voltage supply. diode change due to voltage changes is observed. changes of the diode is recorded in Table 1. observation is discussed.

B. Under voltage Indicator Components:

1. 2. 3. 4. 5. 6. 7. 8. 9.

10kΩ resistor 680Ω resistor 4.7kΩ resistor 4.7MΩ resistor 43Ω resistor L.E.D 0.68uF capacitor PN2907 transistor PN2222 transistor

×1 ×1 ×1 ×1 ×1 ×1 ×1 ×1 ×1

Procedures: + Vref

-

+ Vin

-

1. 2. 3. 4.

The circuit shown in diagram is constructed. 3V (around 0.07A) is supplied to Vref. Vin with voltage below 3V and above is supplied, the difference is observed. 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 undervoltage indicator is combined by gathering both Vref of voltage level detector and undervoltage indicator while VBat of voltage level detector with Vin of undervoltage 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:

Observation Diode Gree Yello Red n w

Voltage (v) 5.0 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

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)

Observation Diode Green Yellow

Vref

Vin

LED

5.0

5.0 4.5 < V < 5.0 4.5

Not flash

On

On

On

Flash

On

On

On

Flash

Off

On

On

5.0 5.0

Red

5.0 5.0 5.0 5.0 5.0

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

Flash

Off

On

On

Flash

Off

Off

On

Flash

Off

Off

On

Flash Flash

Off Off

Off Off

Off Off