Aim:
The aim of this assignment is to build a circuit to measure the intensity of light in both dark and light. I will show that when light falls on the LDR, its resistances will be different from when light doesn’t fall on the LDR. The level of resistance will be measured using the QBASIC program on the computer. Measuring light intensity is made by devices such as sensors and transducers. The sensor is responsive to changes in the quantity of light. The transducer converts such measurement into electrical signals, which can be fed to a computer for readout
Task A
The type of signal I chose to measure in my circuit is light intensity. I did this by using a light dependent resistor (LDR), which detects the changes in light level and thus responded in changing its resistance.
Apparatus:
- LDR
- Potential meter
- Multimeter
- Power supply
- Circuit block
- Wire
- 470 carbon resistor(x2)
- 10k carbon resistor
- wire cutter
Method:
I put my LDR near point A in series with resistors of 10k . I then put 470 resistor between point B and C in parallel to the LDR. The potentiometer was placed in series with 470 resistor near point C. Another resistor which is also 470 was fitted in series to the potentiometer near point D. A power pack was used and the positive terminal of the power back was then fitted at point B. The negative terminal of the power pack was connected to the ground of the circuit at point D. Once I done this I will measure the voltage from point C and D using a multimeter was used at point C and th negative terminal of the multimeter was used at point D. I turned the potential meter from one extreme end and then quarterly (1/4,1/2,3/4) until the other extreme end is reached. This is done to measure the output voltage from the sensor section in light and dark. I took these readings using a multi meter.
See Diagram in next page
Results:
These results are taken from the sensor section of my circuit. As seen in the diagram these are measured between points C and D.
WE GOT THE BIGGEST DIFFENCE IN READINGS WHEN THE POTENTIAL METER WAS TO ONE EXTREME END.
COULD BE ERRORS IN READINGS AS THE WIRES AND COMPENTS WEREN’T HELD DOWN OR TOUNCING PROPERLY.
TASK B:
I am going to use a 741 op-amp in my signal condition section. An operational amplifier is a very high input impedance and low out put impendence. I will connect this to sensor section for it to act as a transistor once I have built the signal condition section to find out the change of voltage of the LDR when in both light and dark to which the potential meter is turned to different positions.
Apparatus:
- power supply
- multimeter
- 741 op-amp
- 10 k carbon resistor
- wires
- circuit block
Turn to next page for how signal conditioning section is connected to the sensor section.
Results:
These results are taken from the signal conditioning section between points F and G
TASK C
My next task is to now build an Analogue to digital converter section (ADC), which I did on the second circuit board.
In order for me to successfully complete the analog to digital conversion using the ADC0804LCN 8-bit A/D converter. I will need to design a circuit and to program the chip so that when an analog signal is given as an input, the corresponding digital voltage will be displayed in the computer screen. The effect of this conversion is that the circuit acts and functions like a voltmeter.
Apparatus needed:
- ADC0804LCN
- 1 K RESISTOR
- 10K RESISTOR
- WIRES
- POWER SUPPLY (X2)
- CIRCUIT BOARD
- MULTIMETER
- WIRE CUTTER
Method
To build the ADC section of the circuit I used wires, which were connected to pin number, 11, 12, 13, 14 and 15 of the analogue to digital converter. before the wires are connected to the computer parallel port I first measured their voltages when the LDR was both in light and dark.
Pin Number and Analogue to digital converter 0804 LCN 8 bit diagrams both in next page.
Results:
These are the values of the wire 11, 12, 13, 14 and 15 that I got when the LDR was in light and dark. the readings are the output section of the ADC section of the circuit, which was in turn connected to the signal conditioning section and this was also connected to the sensor section.
TASK D
When connecting the circuit to the computer I connected the pins of the ADC to the parallel port of the computer.
I connected the wires of the parallel ports on the computer like this.
pin 11 from the Analogue to Digital Converter