Presentation on DESIGN AND CONSCTRUCTION OF A COMPUTER BASED DIGITAL Luxmeter
OBJECTIVES
- Design and construction of Digital to measure the intensity of light.
- To remove the drawback of measurement technique.
- To make the project cost effective.
- To study the working principle of Luxmeter.
METHODOLOGY
Light is measured by using a light sensor in a resistive bridge circuit. Appropriate light range is selected for the sensor calibrating the bridge meter. When light incident on the sensor it will create a voltage across a bridge circuit. We have to amplify this analog voltage and apply to input of ADC for analog to digital conversion. The output of ADC are applied to the input of multiplexer. The output of multiplexer is connected to parallel port of the PC. PC reads this output voltage. We write matlab code for parallel port interfacing . PC reads this voltage and give lux values from relationship between voltage and lux.
Luxmeter
A Luxmeter is a powerful tool which is used to measure the light intensity. We can use it to identify significance energy savings. We can use our Luxmeter to pinpoint over light areas in our office then delamp to reduce energy consumption. We can measure luxlevels using the Luxmeter at 4-5 different point in each points in each room either at night or at around two hours after sunrise or before sunset. Luxmeter is very useful in garment industry. It is useful to identify which light will be used for ironing and which light will be used for sewing purpose etc.
COMPUTER BASED DIGITAL LUXMETER
It is very simple in design. Operating principle is very easy. Total cost is very low. It can measure light in any place. It can store data for long time. Continuous monitoring is possible. Data can be analysis for various experimental works.
DESIGN PROCEDURE
LDR AS LIGHT SENSOR
LDR is an electronic component whose resistance decreases with increasing incident light intensity and vice versa. This is the main principle to measure light intensity in our project. Light is sensed by LDR and we get corresponding output signal.
WHEATSTONE BRIDGE CIRCUIT
Wheatstone bridge circuit is used to find the output voltage that corresponds to the values of the LDR that changes according to the light intensity.
INSTURMENTATION AMPLIFIER
The instrumentation amplifier circuit is used for the amply of the output voltage across the bridge circuit.
The amplified output voltage
V0 = (E1 – E2)(1+2/a)
Where, a = aR/R
Fig: Instrumentation Amplifier
DATA FOR TESTING ADC(0804)
| ANALOG VOLTAGE(V) | DECIMAL VALUE |
| 0.526 | 16 |
| 0.863 | 40 |
| 1.398 | 64 |
| 2.005 | 96 |
| 2.509 | 112 |
| 3.086 | 152 |
| 3.46 | 168 |
| 4.04 | 200 |
| 4.47 | 224 |
| 4.9 | 248 |
DATA COLLECTION FOR LUXMETER
| LUX | VOLTAGE( V) |
| 14 | 4.16 |
| 18 | 3.108 |
| 23 | 2.419 |
| 29 | 1.933 |
| 37 | 1.439 |
| 42 | 1.34 |
| 47 | 1.209 |
| 50 | 1.123 |
| 55 | 1.034 |
| 60 | .952 |
| 63 | .923 |
| 68 | .855 |
Lux vs. Voltage curve
PARALLEL PORT INTERFACING WITH PC
Parallel port is widely used for interfacing hand made project and large implementation. The voltage levels of parallel ports are 0 volt for logic low and 5 volt for logic high. All the bits are available simultaneously in the parallel port, the need for additional hardware is eliminated. Data transfer rate of parallel port is considerably faster.
CIRCUIT DIAGRAM
CIRCUIT CONNECTION IN PROJECT BOARD
CONCLUSION AND FUTURE WORK
We have selected this computer based digital Luxmeter for various purposes. One of the main reasons is that we can store lux values for different illumination in computer systems. In future we can analysis this lux values. This analysis is sometimes very important for experimental work. Again in this time computer system is very available in every place. So we can measure lux values very easily. We have tried our best to construct our Luxmeter very cheaply. If any electronic company use our design to manufacture digital Luxmeter, it will cheaper than imported Luxmeter. So it can save huge amount of foreign currency.
Submitted by Md. Moniruzzaman and Md. Mehedi Hasan