Counter variable won't increment/decrement within a continuous DAQ function?

I'm attempting to create a script which creates a different event for even- and odd-numbered trigger instances (essentially just outputting either 1 or 0), but have run into a brick wall where the counter variable never changes. This script has been written for a NI DAQ device, and is using the Data Acquisition Toolbox Analog Input Recorder setup with a continuous session in the background. What can I do to fix this issue, and have the counter variable actually store its new variables throughout the DAQ session?

Here is some sample code:

% Create Data Acquisition Session

% Create a session for the specified vendor.

s = daq.createSession('ni');

% Set Session Properties

% Set properties that are not using default values.

s.IsContinuous = true;

% Add Channels to Session

% Add channels and set channel properties, if any.

addAnalogInputChannel(s,'Dev1','ai0','Voltage');

% Initialize Session UserData Property

% Initialize the custom fields for managing the acquired data across callbacks.

var1 = 240; % Constant scaling value

i = 0; % Simple counter variable

s.UserData.Data = [];

s.UserData.Data(1) = 0;

s.UserData.TimeStamps = [];

s.UserData.StartTime = [];

% Add Listeners

% Add listeners to session for available data and error events.

lh1 = addlistener(s, 'DataAvailable', @(src, eventData) recordData(src, eventData, var1, i));

% Acquire Data

% Start the session in the background.

startBackground(s)

% Callback Function

% Define the callback function for the 'DataAvailable' event.

function recordData(src, eventData, var1, i)

% RECORDDATA(SRC, EVENTDATA) records the acquired data, timestamps and

% trigger time. You can also use this function for plotting the

% acquired data live.

% SRC - Source object i.e. Session object

% EVENTDATA - Event data object i.e. 'DataAvailable' event data object

% Record the data and timestamps to the UserData property of the session.

src.UserData.Data = [src.UserData.Data; eventData.Data];

src.UserData.TimeStamps = [src.UserData.TimeStamps; eventData.TimeStamps];

constant = mean(src.UserData.Data(1:100)); %Washes out drift from initial baseline sensor measurements

data1 = (((eventData.Data-constant)*112.405)*2); % Convert data into relevant units

data = smoothdata(data1,'movmedian'); % Display data with live smoothing

% Record the starttime from the first execution of this callback function.

if isempty(src.UserData.StartTime)

src.UserData.StartTime = eventData.TriggerTime;

end

% Process Data

if data(end) > (PartLB*.025) && data(end) < (PartLB*0.15) && data(end-50) < data(end) % Setting simple sensor triggering threshold

if i == 0

disp('even')

i = i + 1;

end

if i == 1

disp('odd')

i = 0;

end

end

% Uncomment the following lines to enable live plotting.

plot(eventData.TimeStamps, data)

xlabel('Time (s)')

ylabel('Amplitude (V)')

% xlim([0 500])

ylim([-30 var1])

legend('ai0')

end

Answer 1

[Voss]

Maybe the problem is this:

if i == 0
    disp('even')
    i = i + 1;
    % i is now 1
end

% at this point:
%   if i was 0 before the previous if, it is now 1
%   if i was 1 before the previous if, it is now 1
% 
% therefore, the 2nd if condition below is true whether i was 0 or 1
% before the first if above

if i == 1
    disp('odd')
    i = 0;
    % i is now 0
end

% at this point i is 0 regardless of whether it was 0 or 1 before the first if

You can try this instead:

if i == 0
    disp('even')
    i = i + 1;
elseif i == 1
    disp('odd')
    i = 0;
end