[Paper Review] Low Cost PC Based Real Time Data Logging System Using PCs Parallel Port For Slowly Varying Signals

Nungleppam Monoranjan Singh, Kamal Sarma|arXiv (Cornell University)|Jul 11, 2012

Sensor Technology and Measurement Systems7 citations

TL;DR

This paper presents a low-cost, PC-based real-time data logging system using a parallel port to monitor slowly varying signals like temperature and humidity. It employs an LM35 sensor, ADC0808 for analog-to-digital conversion, and a C-programmed interface to log data at 2 samples/second with 0.2°C resolution, storing results in CSV format for Excel analysis and enabling real-time graphical display and automatic calculation of relative humidity and dew point.

ABSTRACT

A low cost PC based real time data logging system can be used in the laboratories for the measurement, monitoring and storage of the data for slowly varying signals in science and engineering stream. This can be designed and interfaced to the PCs Parallel Port, which is common to all desktop computers or Personal Computers (PCs). By the use of this data logging system one can monitor, measure and store data for slowly varying signals, which is hard to visualise the signal waveforms by ordinary CRO (Cathode Ray Oscilloscope) and DSO (Digital Storage Oscilloscope). The data so stored can be used for further study and analysis. It can be used for a wide range of applications to monitor and store data of temperature, humidity, light intensity, ECG signals etc. with proper signal conditioning circuitry.

Motivation & Objective

• To develop a low-cost, real-time data acquisition system for monitoring slowly varying physical parameters such as temperature and humidity.
• To utilize the parallel port of a PC as a cost-effective interface for data input, avoiding expensive data acquisition hardware.
• To enable real-time graphical display and long-term storage of sensor data for post-analysis using standard software like Excel.
• To automatically compute and log relative humidity and dew point using dry and wet bulb temperature readings.
• To ensure compatibility with both new and legacy PCs, including desktops and laptops, by leveraging widely available parallel port interfaces.

Proposed method

• Analog temperature signals from an LM35 sensor are conditioned using a low-offset, high-gain operational amplifier to scale the output to 0–5 V.
• An anti-aliasing low-pass filter is applied to prevent spectral distortion, ensuring signal fidelity before ADC conversion.
• An ADC0808 converts the analog signal into an 8-bit digital value (resolution ≈19.6 mV or 0.2°C) at a sampling rate of 2 samples per second.
• A clock circuit using IC 7414, a resistor, and a ceramic capacitor generates a stable clock signal with frequency f = 1/(1.1RC) to control the ADC.
• A voltage-limiting circuit using zener diodes protects the ADC from overvoltage by clamping the output to 5 V.
• A C-programmed application controls the parallel port to read digital data, display real-time temperature graphs, and save data in .csv format for Excel compatibility.

Experimental results

Research questions

• RQ1 Can a parallel port be effectively repurposed for real-time data acquisition of slowly varying analog signals in a low-cost setup?
• RQ2 What is the achievable resolution and accuracy of a data logger using an ADC0808 and LM35 sensor via a PC parallel port?
• RQ3 How accurately can relative humidity and dew point be computed using dry and wet bulb temperature readings in such a system?
• RQ4 To what extent does the system maintain data integrity and real-time performance under typical environmental conditions?
• RQ5 Can this low-cost system serve as a viable alternative to commercial data loggers in educational and basic industrial monitoring?

Key findings

• The system achieves a temperature resolution of approximately 0.2°C (0.0196 V per LSB) due to the 8-bit ADC0808 and 5 V reference.
• The data logging system operates at a stable sample rate of 2 samples per second, adjustable via software modifications.
• The system successfully computes and logs relative humidity (85.18%) and dew point (17.36°C) in real time using dry and wet bulb temperature inputs.
• Measured data from the system showed satisfactory agreement with mercury thermometer readings, confirming acceptable accuracy despite noise and shielding limitations.
• The system enables real-time graphical monitoring of temperature and automatic saving of data in .csv format, which is directly compatible with Microsoft Excel.
• The use of zener diodes for overvoltage protection effectively prevents ADC damage and enhances system reliability.