How do I read voltage on multiple channels using the 6255\SCB-6​8

Question

Hi All
I was able to get the following code to compile, run and view the voltage data as expected. when reading the voltage (RSE) on Dev0/ai65
...National Instruments\NI-DAQ\Examples\DAQmx ANSI C\Analog In\Measure Voltage\Cont Acq-Int Clk\ContAcq-IntClk.c
* I think that I am using RSE but I have no clue since I do not see an argument to specify
I am trying to read two different data points:
1. View the voltage (RSE) on Dev0/ai65
2. View the voltage difference (Differential) between Dev0/ai17 and Dev0/ai25
Can someone point me to an example (or web link) where two different data points are being read.
*edit - I am trying to complete this task using C++
Thanks
Chad
Solved!
Go to Solution.

Answer 1

This was my last attempt that failed
#include <stdio.h>
#include <NIDAQmx.h>
#include <iostream>
using namespace std;
#define DAQmxErrChk(functionCall) if( DAQmxFailed(error=(functionCall)) ) goto Error; else
int32 CVICALLBACK EveryNCallback(TaskHandle taskHandle1, int32 everyNsamplesEventType, uInt32 nSamples, void *callbackData);
int32 CVICALLBACK EveryNCallback(TaskHandle taskHandle2, int32 everyNsamplesEventType, uInt32 nSamples, void *callbackData);
int32 CVICALLBACK DoneCallback(TaskHandle taskHandle1, int32 status, void *callbackData);
int32 CVICALLBACK DoneCallback(TaskHandle taskHandle2, int32 status, void *callbackData);
int main(void)
 cout << "\t***********************************************​****\n";
 cout << "\t         Starting the NI DAQmx data logger\n";
 cout << "\t***********************************************​****\n\n";
 int32       error = 0;
 TaskHandle  taskHandle1 = 0;
 TaskHandle  taskHandle2 = 0;
 char        errBuff[2048] = { '\0' };
 // DAQmx Configure Code
 DAQmxErrChk(DAQmxCreateTask("task1", &taskHandle1));
 DAQmxErrChk(DAQmxCreateTask("task2", &taskHandle2));
 DAQmxErrChk(DAQmxCreateAIVoltageChan(taskHandle1, "Dev1/ai65", "", DAQmx_Val_Cfg_Default, -10.0, 10.0, DAQmx_Val_Volts, NULL));
 DAQmxErrChk(DAQmxCreateAIVoltageChan(taskHandle2, "Dev1/ai17", "", DAQmx_Val_Cfg_Default, -10.0, 10.0, DAQmx_Val_Volts, NULL));
 DAQmxErrChk(DAQmxCfgSampClkTiming(taskHandle1, "", 10000.0, DAQmx_Val_Rising, DAQmx_Val_ContSamps, 1000));
 DAQmxErrChk(DAQmxCfgSampClkTiming(taskHandle2, "", 10000.0, DAQmx_Val_Rising, DAQmx_Val_ContSamps, 1000));
 DAQmxErrChk(DAQmxRegisterEveryNSamplesEvent(taskH​andle1, DAQmx_Val_Acquired_Into_Buffer, 1000, 0, EveryNCallback, NULL));
 DAQmxErrChk(DAQmxRegisterEveryNSamplesEvent(taskH​andle2, DAQmx_Val_Acquired_Into_Buffer, 1000, 0, EveryNCallback, NULL));
 DAQmxErrChk(DAQmxRegisterDoneEvent(taskHandle1, 0, DoneCallback, NULL));
 DAQmxErrChk(DAQmxRegisterDoneEvent(taskHandle2, 0, DoneCallback, NULL));
 // DAQmx Start Code
 DAQmxErrChk(DAQmxStartTask(taskHandle1));
 DAQmxErrChk(DAQmxStartTask(taskHandle2));
 printf("Acquiring samples continuously. Press Enter to interrupt\n");
 getchar();
Error:
 if (DAQmxFailed(error))
  DAQmxGetExtendedErrorInfo(errBuff, 2048);
 if (taskHandle1 != 0) {
  // DAQmx Stop Code
  DAQmxStopTask(taskHandle1);
  DAQmxStopTask(taskHandle2);
  DAQmxClearTask(taskHandle1);
  DAQmxClearTask(taskHandle2);
 if (taskHandle2 != 0) {
  // DAQmx Stop Code
  DAQmxStopTask(taskHandle1);
  DAQmxStopTask(taskHandle2);
  DAQmxClearTask(taskHandle1);
  DAQmxClearTask(taskHandle2);
 if (DAQmxFailed(error))
  printf("DAQmx Error: %s\n", errBuff);
 printf("End of program, press Enter key to quit\n");
 getchar();
return 0;
int32 CVICALLBACK EveryNCallback(TaskHandle taskHandle, int32 everyNsamplesEventType, uInt32 nSamples, void *callbackData)
 //cout << "\nStarting EveryNCallback" << "\n";
 //cout << "line 59" << "\n";
 TaskHandle  taskHandle1 = 0;
 TaskHandle  taskHandle2 = 0;
 int32       error = 0;
 char        errBuff[2048] = { '\0' };
 static int  totalRead1 = 0;
 static int  totalRead2 = 0;
 int32       read1 = 0;
 int32       read2 = 0;
 float64     data1[1000];
 float64     data2[1000];
 // DAQmx Read Code
 cout << "Start DAQmx Read Code Loop \n";
 DAQmxErrChk(DAQmxReadAnalogF64(taskHandle1, 1000, 10.0, DAQmx_Val_GroupByChannel, data1, 1000, &read1, NULL));
 DAQmxErrChk(DAQmxReadAnalogF64(taskHandle2, 1000, 10.0, DAQmx_Val_GroupByChannel, data2, 1000, &read2, NULL));
// for (int i = 0; i <= 10; i++)
//  cout << data[i] << "\n";
 //cout << "Here is data = " << data << "\n";
 //cout << "Here is data[2] = " << data[2] << "\n"; // write the data to a file
 if (read1>0) {
  cout << "Acquired " << read1 << " samples \n";
  totalRead1 += read1;
  cout << "Acquired " << totalRead1 << " Total samples \r\n\n";
  cout << data1 << "," << data2 << "\n";
  fflush(stdout);
 // cout << "the next line is stdout \n";
 // cout << stdout << "\n";
Error:
 if (DAQmxFailed(error)) {
  DAQmxGetExtendedErrorInfo(errBuff, 2048);
  // DAQmx Stop Code
  DAQmxStopTask(taskHandle1);
  DAQmxStopTask(taskHandle2);
  DAQmxClearTask(taskHandle1);
  DAQmxClearTask(taskHandle2);
  printf("DAQmx Error: %s\n", errBuff);
 return 0;
int32 CVICALLBACK DoneCallback(TaskHandle taskHandle, int32 status, void *callbackData)
 cout << "\nStarting DoneCallback" << "\n";
 cout << "line 99" << "\n";
 int32   error = 0;
 char    errBuff[2048] = { '\0' };
 // Check to see if an error stopped the task.
 DAQmxErrChk(status);
Error:
 if (DAQmxFailed(error))
  TaskHandle  taskHandle1 = 0;
  TaskHandle  taskHandle2 = 0;
  cout << "line 109" << "\n";
  DAQmxGetExtendedErrorInfo(errBuff, 2048);
  DAQmxClearTask(taskHandle1);
  DAQmxClearTask(taskHandle2);
  printf("DAQmx Error: %s\n", errBuff);
 return 0;