Welcome to the NAU Capstone Design pages. We are (pictured from left to right) David Sharik, Thomas Carr, and Franklin Brady. As part of our electrical engineering course work, we were required to complete an industry sponsored capstone design project. Our project was a Microprocessor (Intel 80C51) Controlled Data Acquisition System, sponsored by the Dataforth Corporation, of Tucson, AZ.

Problem Definition

Dataforth designs and manufactures a line of signal conditioning modules. These modules convert an external excitation (temperature, resistance, current, etc.) to a large signal voltage (typically in the range of 0 to +5 volts). We were requested to design and implement a Data Acquisition System (DAS) that would scan the outputs of several modules, convert the voltage to digital, and store the resulting conversion values in a RAM database. Additionally, the DAS was to maintain a running average for each input and support serial communications with a PC.

Solution

 The following block diagram details our proposed solution:

A multiplexer network selects in sequence one of sixteen differential inputs. After the input is passed through the multiplexer an instrumentation amplifier converts the differential signal to single-ended. Finally, a twelve-bit, successive approximation ADC performs the conversion to digital.

The CPU is an Intel 80C51 single chip microcontroller. This block, in conjunction with a timer, initiates input selection and data conversions. When a conversion value from the ADC becomes available, the CPU reads the data, calculates an average, and stores the latest conversion value (raw data) and the average in a database (Static RAM).

A PC may transmit commands and receive data across a serial cable. Commands request data (raw or average on any input), alter the sampling rate, change the number of past values to maintain the running average over, and halt or resume collecting data. Additionally, a unique designation may be assigned to the DAS. Commands from the PC must be prefixed with the proper designation code, else the command will be ignored. In this manner, multiple devices may be attached to the same serial network.

Implementation

Pictured below is the actual DAS built for Dataforth. This device was successfully tested and demonstrated at the NAU Capstone Design Conference on April 25^th, 1997.

A 37 D-shell connector (bottom right) provides connections for each of the 16 differential inputs. A Personal Computer accesses data by issuing the proper commands through the 9 pin serial port (top right). Power (+5 volts, +/- 12 volts) is supplied externally through the cable emitting from the right side of the breadboard.

Back to College of Engineering Home Page