Presented here is a USB data acquisition system that can be used to interface six sensors and four digital-to-analogue channels. The acquired voltage levels can be displayed on a personal computer (PC). The DAQ device may be calibrated for precision and benchmarked with various standards, and delivered as an inexpensive USB DAQ product for hobbyists and students.
Irrespective of our stream of engineering or science, most of us do programming and data analysis on computers due to ease in data handling, storage and manipulation.
This project may be helpful for those who want to develop an integrated system that consists of a DAQ and other system circuitry in a single unit. It would provide a greater insight to the design and development of a USB DAQ system itself! The article includes details of circuit designs, software development for user-interface using C# and LabView, printed circuit board (PCB) development and test results.
It is assumed that the reader is familiar with basic ‘C’ programming and AVR programming styles. However, best efforts have been made to make the contents logical enough to help even a beginner understand the project and tweak with the codes.
Typically, the output from a sensor is available in the form of a voltage signal. For example, the output from a commonly used temperature sensor like LM35 is 10mV/°C under normal environmental conditions, which varies linearly with temperature. Hence you can calibrate the measured voltage to the temperature of the surroundings it is being interfaced with. Same is the case with a pressure sensor, LVDT, etc.
You may also need to trigger a device from a PC with a voltage signal, or you may require a dynamically changing voltage level to drive a certain drive system, e.g., a linear servo motor. You may also require to count an event which is signaled by a voltage pulse, such as in flywheel counters or robotic shaft encoders.
Most of the commercially available DAQ systems come with all the above-mentioned features of counters, analogue inputs and outputs, digital inputs and outputs, etc. However, these systems are quite expensive and come with a paid driver for interfacing. Most of them can only be used with the proprietary software of the manufacturer.
This project is intended for those who want to make their own system for data acquisition due to the limitation of their total project cost or installation where one cannot use commercially available DAQ (such as in a nuclear or defense installation). The author’s prototype is shown in Fig. 1.