Timer encounters error on non-structure array

Trying to use Timer in GUI. While attempting in following code it is showing error.

    function main_OpeningFcn(hObject, eventdata, handles, varargin)
      handles.output = hObject;
      handles.timer   = timer(...
      'ExecutionMode', 'fixedRate', ...       % Run timer repeatedly
      'Period', 1, ...                        % Initial period is 1 sec.
      'TimerFcn', {@send_Callback,hObject});
      guidata(hObject, handles);

    function send_Callback(hObject, eventdata, handles)
      comma      = get(handles.Tx_send, 'String');%Tx_send is a text field
      TxText     = char(comma);
      sf         = rc4e2(TxText,key);%rc4e2 is an encryption
      key        = TxText;
      DBC        = char(sf);
      disp(DBC);
      fwrite(handles.serConn, DBC);%serConn is COM port

The error: Error while evaluating TimerFcn for timer 'timer-1'. Attempt to reference field of non-structure array.

Answer 1

[Jan]

   'TimerFcn', {@send_Callback,hObject}

Now the 3rd input of send_Callback is hObject, the handle provided to the Opening-function. It is not clear, why you store this handle in the field "output". In the callback send_Callback it seems like you expect the 3rd input to be the handles struct and access the fields Tx_send and serConn, but here handles is the graphics handle.

I guess you want something like this:

function send_Callback(hObject, eventdata, hObject)
handles = guidata(hObject);
...