manufacturer of I/O-rich SBCs, operator interfaces, handheld instruments, and development tools for embedded control low cost single board computers, embedded controllers, and operator interfaces for scientific instruments & industrial control development tools for embedded control order our low cost I/O-rich embedded control products embedded controller manufacturer profile single board computers & embedded controllers development tools & starter kits for your embedded design operator interfaces with touchscreens and graphical user interface plug-in expansion modules for digital & analog I/O C language & Forth language integrated development tools, IDE single board and embedded computer accessories embedded controller enclosures, bezels, environmental gaskets
Table of Contents

Introduction

Connecting to the 24/7 Data Acquisition Module

Hardware

On-Board Reference

Digital Inputs

Analog Inputs

Programmable Gain

Input Protection

Allowable Input Impedance

Converter Noise and Effective Resolution

Other Sources of Noise and Offset Error

Tips For Measuring Small Voltages

Addressing the 24/7 WildCard Using Module Select Jumpers

Software

Initializing the 24/7 Data Acquisition Wildcard

Specifying the Reference Voltage

Starting a Conversion

Calibration Options
Choosing the Sample Rate
Setting the Gain
Choosing Bipolar or Unipolar Conversion
Specifying 16- or 24-bit Resolution
Synchronizing Conversions
Specifying the Source Channels

Obtaining A Sample

Single- and Multi-Channel Sampling

Continuous Sampling from a Single Channel
Sequential Sampling from Several Channels

C Example Listing (pdf)

Forth Example Listing (pdf)

Glossary

Appendix A:24/7 Data Acquisition Wildcard Pin-outs

Appendix B:24/7 Data Acquisition Wildcard Schematics (pdf)

24/7 Data Acquisition Wildcard Users Guide

<< Previous | Next>>

Setting the Gain

The gain option is specified as a constant to Start_Conversion or Start_Conv_With_Values. Valid constants are GAIN_1, GAIN_2, GAIN_4, GAIN_8, GAIN_16, GAIN_32, GAIN_64, or GAIN_128. Saturation will occur if the absolute value of the input signal multiplied by the gain is greater than 2.5 volts.

Choosing Bipolar or Unipolar Conversion

Passing the UNIPOLAR or BIPOLAR constant to Start_Conversion or Start_Conv_With_Values sets the polarity option for the module. The 24/7 Data Acquisition Wildcard accepts either unipolar or bipolar input voltage ranges. Bipolar input ranges do not imply that the part can handle negative voltages below -20 mV on its analog inputs! The input channels are arranged in pairs with an Analog In + and Analog In −. As a result, the voltage to which the unipolar and bipolar signals on the Analog In + input are referenced is the voltage on the respective Analog In − input. For example, if Analog In − is +2.5 V and the module is configured for unipolar operation with a gain of 2 and a reference voltage of +2.5 V, the input voltage range on the Analog In + input is +2.5 V to +3.75 V. If Analog In − is +2.5 V and the module is configured for bipolar mode with a gain of 2 and a reference voltage of +2.5 V, the analog input range on the Analog In + input is +1.25 V to +3.75 V (i.e., 2.5 V +/- 1.25 V).

Specifying 16- or 24-bit Resolution

The 24/7 Data Acquisition Wildcard has two resolution settings: 16 and 24 bit. The 16 bit resolution option is used when the constant WORD_16BIT is passed to Start_Conversion or Start_Conv_With_Values. The 24 bit option is used when the constant WORD_24BIT is passed to Start_Conversion or Start_Conv_With_Values. Changing the resolution only changes the data size; it does not affect the conversion process.

Turning the Burnout Current Option On/Off

The analog to digital converter contains two 1 ?A currents, one source current from the analog power supply to the current Analog In + and one sink from Analog In − to analog ground. The currents are either both on or both off depending on the constant, BO_ON or BO_OFF, that is passed to Start_Conversion or Start_Conv_With_Values. You can use these currents to see if a transducer has burned out or gone open-circuit before attempting to take measurements on that channel. If the transducer becomes an open-circuit with the burnout currents on, the input voltage will be measured as full scale. If the transducer becomes a short circuit with the burnout currents on, the input voltage will be measured as zero.

Synchronizing Conversions

The synchronization option allows you to reset the modulator and the digital filter of the analog to digital converter without affecting any other settings such as gain, channel, polarity, or calibration values. This allows conversions to be started at a precisely known time. To start a synchronous conversion, pass FSYNC_ON to Start_Conv_With_Values or call Sync, which synchronizes the conversion through a hardware pin. A valid sample will be available 3 sample periods (3/sample frequency) later. For example, if the sample frequency is 10 Hz, the channel has already been calibrated, and Sync is called, the next sample will be available after 300 ms (3 / 10 Hz). The synchronization option should not be used when a Background Calibration is operating.

Specifying the Source Channels

Table 1 lists the options available for channel selection.

<< Previous | Next>>


Home|Site Map|Products|Manuals|Resources|Order|About Us
Copyright (c) 2006 Mosaic Industries, Inc.
Your source for single board computers, embedded controllers, and operator interfaces for instruments and automation