Physics can be interesting and boring at the same time. It might get boring for the reason that most of the physical parameters vary frequently with values or physical properties they execute and we lack apparatus to measure them accurately. This leads us to the fact that we cannot get a precise measurement. The project described here is a simple PC-based project (PC-based data logger) which can be used in physics laboratories with the purpose to automate simple experiment or to monitor slowly varying physical variables such as temperature. The wide range of operating voltage +5V to -5V at the data rate of 18 samples/second with resolution of 39.2 mV makes this circuit more versatile and attractive at the same time.
Circuit Description of Data Logger Using Computer:-
This circuit of data logger using computer alone employs three main particular ICs, each configured in different mode of operation. An analog to digital converter IC ADC0804 (IC7) is the heart of this project which is accompanied by another IC LF398 (IC6) configured as sample and hold IC and operational amplifier IC (IC5). The analogue input is fed to the op-amp IC5 through pin no.3 via resistor R4. Keeping in mind to present same input values, same value of two resistors; R3 and R4 are used to supply series input to the corresponding IC as shown in the circuit diagram. The combination of biasing resistor (R5) and feedback resistor (R3) and input resistor provide an overall gain of 0.5.
The relationship between input and output voltage obtained at pin 6 of IC5 is given by the expression below-
V0 = (Vin +5)/2
The output thus obtained from IC5 is given to the pin 3 of IC6 configured as sample and hold amplifier. To configure IC in sample and hold mode, a signal is passed to pin 8 of IC6 from computer through parallel port pin 14. Here capacitor C5 (poly propylene), serves as a charge holding component connected to pin 6 of IC6. The control signal logic 1 puts IC6 in simple mode and logic 0 puts in hold mode. Pin 6 of ADC IC7 receives the output from IC6.
The ADC IC7 transforms analogue input (i.e. output from IC6) into digital (binary) values.
Three particular pins control the operation of IC7 in following ways-
|1||Chip-set (CÌ…S),||Logic 0 on CS and RD pin enable the IC and ADC conversion is initiated,|
|3||Write(WÌ…R)||Logic-low to high; conversion of analog signal to binary signal is held.|
Similarly, for INTR pin-
Logic 0- the conversion is over
Logic 1- the conversion is started
The converted signal from INTR is applied to the inverter IC8, which is then fed to pin 10 of parallel port as illustrated in the figure.
The data pins 11-18 of ADC IC7 are interfaced to pins 2-9 of parallel port. For further details, go through the table 1.
The control bit 1 is used to control sample /hold IC (IC6) where logic 0 and logic 1 is provided from pin 14 to pin 8 when control bit is high and low respectively. Control bit 2 is connected to WÌ…R pin of ADC through diode D5.
PARTS LIST OF DATA LOGGER USING COMPUTER
|Resistor (all ¼-watt, ± 5% Carbon, unless stated otherwise)|
|R1 = 470 Ω
R2, R4 = 20 KΩ
R3, R5, R8 = 10 KΩ
R6, R7 = 1 KΩ
|C1 – C4 = 1000 µF, 25V (electrolytic capacitor)
C5 = 0.01 µF (ceramic disc capacitor)
C6 = 150 pF (ceramic disc capacitor)
|IC1 = 7812 (+12V regulator)
IC2 = 7805 (+5V regulator)
IC3 = 7912 (-12V regulator)
IC4 = 7905 (-5V regulator)
IC5 = OP-07 (operational amplifier)
IC6 = LF398 (sample and hold amplifier)
IC7 = ADC0804analogue-to-digital converter
IC8 = 74LS04 (hex inverter)
D1 – D5 = 1N4007 (rectifier diode)
LED1 = LED (power-indicator)
|X1 = 230V/50Hz or 110/50Hz AC primary to 15V-0V-15V, 1A secondary step-down transfer
25-pin D type female connector
Two 25-pin D type male connector (for connecting two circuit to the female connector at the back of the PC and circuit)
Register Pin Detail of the PC’s Parallel Port
|Parallel Port pin NO.||Signal Name||Direction||Register bit||Inverted|
|1||nStrobe||Out||Control – 0||Yes|
|2||Data0||In/Out||Data – 0||No|
|3||Data1||In/Out||Data – 1||No|
|4||Data2||In/Out||Data – 2||No|
|5||Data3||In/Out||Data – 3||No|
|6||Data4||In/Out||Data – 4||No|
|7||Data5||In/Out||Data – 5||No|
|8||Data6||In/Out||Data – 6||No|
|9||Data7||In/Out||Data – 7||No|
|10||nAck||IN||Status – 6||No|
|11||Busy||IN||Status – 7||Yes|
|12||Paper-Out||IN||Status – 5||No|
|13||Select||IN||Status – 4||No|
|14||Linefeed||Out||Control – 1||Yes|
|15||nError||In||Status – 3||No|
|16||nInitialize||Out||Control – 2||No|
|17||nSelect-Printer||Out||Control – 3||Yes|
Software:- The fact that the entire process of coding is done in platform of C-programming, extends the flexibility of the project and makes it easy to understand for a wide range of people. However, the input data must be transferred at the rate of one sample per second. The plot of simulated time Vs voltage graph on the monitor screen shown in the figure explains it all.
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