As we all know that physics is most interesting topic but some time we feel uncomfortable to deal with some physics varying variable due to lack of precise practical apparatus. Now, here is simple PC-based project (PC-based data logger), used in physics laboratories for automating simple experiment and or monitoring slowly varying physical variable 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.

Circuit description

The entire hardware circuit of PC-based data logger is designed around analog to digital converter (ADC) IC ADC0804 followed by sample and hold IC LF398 with operational amplifier (op-amp) IC op-07.

The analogue input is given to pin 3 of op-amp IC, configured as differential amplifier through resistor R₄. Resistor R₃ and R₄ of same value for series input to op-amp IC is used here. The gain of amplifier is 0.5 set by feedback resistor, biasing resistor R₃ and R₅ with input resistor.

The swing of output from 0V to +5V is for swing in input -5 to +5V. The output is obtained from pin 6 given to the input pin 3 of IC₆. IC₆ is sample and hold amplifier which get control signal from computer through parallel port pin 14 to pin 8 for sample and hold mode. A poly propylene capacitor C₅ is used as hold capacitor connected to pin 6 of IC₆. The output from pin 5 is given to pin 6 of IC₇ according to control signal logic 1 puts in simple mode while logic 0 puts in hold mode.

The analogue output from sample and hold IC is fed to analogue to digital converter IC₇ for conversion into binary data. The IC₇ is controlled by three pin referred as chip-set (CS), read (RD) and write (WR) inputs. Logic 0 on CS and RD pin enable analogue to digital converter (ADC) and convert data to appear on output pin (11 to 18), where write WR pin occur low-to-high the conversation of analogue signal to binary signal is held. The end-of-conversion signal is done by INTR pin.

Here INTR pin indicate whether the conversion is start or over (i.e. low on INTR pin over the conversion where high starts the conversion and remain up to conversion). The signals from Analogue to Digital converter (ADC) through INTR go to inverter IC, inverted signal fed to pin 10 of parallel port. Digital output D₀ through D₇ of analogue to digital conversion is connected to pin 2 through 9 of parallel port, refer as data pins. Detail of register pin of parallel port is shown in table 1.

Register Pin Detail of the PC’s Parallel Port

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 WR pin of ADC through diode D₅.

The output for 1 Hz square wave and sine wave input with amplitudes of 4V and 5V, respectively, are shown in figure 2

Software:- The source code for data logger is written in C-Programming language for easy to use and understand.

Click Here To Download Source Code of PC-based Data Logger

PCB design:- PCB design of PC-Based Data Logger

Figure 3: Soldering side PCB layout

Figure 4: Component Side PCB Layout

PARTS LIST