ECE 101 Exploring Electrical Engineering Chapter 7 Data Acquisition Herbert G. Mayer, PSU Status 11/30/2015 Derived with permission from PSU Prof. Phillip Wong

Syllabus Data Acquisition Device Analog IO Analog-to-Digital Conversion Digital-to-Analog Conversion Digital IO

2 Data Acquisition Device (DAQ) Multifunction IO unit  Analog input  measures an analog input voltage  Analog output  generates an analog output voltage  Digital input  senses a binary voltage level  Digital output  generates a binary voltage level  Timer  reference time base  Counter  keeps a count of logic events

3 Common types of DAQ hardware:  Internal peripheral card that plugs into an expansion slot on a host computer  External module that connects to a host computer by USB cable, network cable, or wireless. The DAQ is controlled by software on the host.

4 Analog IO How does a DAQ device measure or generate analog voltages? Measure:  An analog-to-digital converter samples an input voltage signal and converts it to digital form. Generate:  A digital-to-analog converter takes digital values and converts them to an output voltage signal.

5 Analog-to-Digital Conversion Analog-to-Digital Converter (ADC or A/D) → A circuit converts an analog signal to a set of numbers that represents the signal’s amplitude at regular time intervals. Definition → Sampling is the process by which the signal is converted to digital values. Analog signal t A/D Conversion Sampling t → → → → 221 : Digital values

6 Digital-to-Analog Conversion Digital-to-Analog Converter (DAC or D/A) → A circuit converts a set of numbers to an analog signal that represents the digital values at sequential points in time. The DAC output typically goes through a reconstruction filter to “smooth out” the signal. t 0 : 0 → t 1 : 3 → t 2 : 5 → t 3 : 5 → : Digital values Analog signal t D/A Conversion Filter

7 Digital IO Digital IO channels allow the DAQ to interface with external digital circuits. A channel can be configured for digital IO:  Input: Senses a logic low or high level signal  Output: Generates a low or high signal t V Logic low Logic high In terms of voltages, a low value is 0 V, and a high value is +5 V (or +3.3 V for some circuits).