- Description:
- The allchan program is a demonstration of how to
sample multiple channels simultaneously from the NIDAQ card.
The access to the card is through the "Easy I/O for DAQ" functions
described in chapter 10 of the LabWindows/CVI Standard Libraries book.
In this program there is an array called channelState which
indicates whether each channel is active or inactive when the
sampling process is running. There are radio buttons on the user interface
which "turn on/off" individual channels. When the "start" button in the
user interface is pressed, a
channel string
is created for the active channels, and continuous sampling is started
with the
AIStartAcquisition
function.
There are two modes in which to access the samples from the NIDAQ card which are stored in an internal circular buffer. The two read modes are (1) CONSECUTIVE_MODE which will not skip any elements stored in the internal circular buffer, and (2) LASTEST_MODE which will read from the writing end of the circular buffer so that the most recent values of the sampling will be read. This program is for displaying the sensor data on screen, so the LATEST_MODE is used, but if you want to send the data to some other code for processing, you probably want to set the read mode to CONSECUTIVE_MODE.
There is one limitation to the "Easy I/O" for DAQ functions: all of the channels will be sampled at the SAME sampling rate. Stanford is missing the book describing the DAQ_* functions which could be used to do parallel sampling of channels at unrelated sampling rates.
An added feature of the allchan program is that you can select the NIDAQ sampling voltage range independently for each channel, so you could have -10 volts to 10 volts for a piezo sensor, while on another channel you can sample in the range from 0 to 5 volts for an FSR for example.
- Zipped Project:
- allchan.zip (version 12 Nov 1998)
- Viewable Code:
- allchan.c (version 12 Nov 1998)
- Code based on:
- Chapter 10 of LabWindows/CVI 4.0.1 Standard Libraries
Reference Manual
- Possible Modification:
-
- Send multi-dimensional sampled data to an analysis filter.
- Implementation note:
- The multi-channel sampling is done with the
"Easy I/O" functions for DAQ. The main functions are:
- AIStartAcquisition -- starts the continuous mutichannel sampling.
- AICheckAcquisition -- sees how many samples are waiting to be processed.
- AIReadAcquisition -- transfers samples from NIDAQ to program.
- AIClearAcquisition -- stops the continuous sampling which was started with the AIStartAcquisition function.
- Screen Capture of User Interface:
-
