Measure
How to acquire analog input driven by digital output? (NI-6251 with Matlab)
- last edited on by
Content Cleaner
Hi krasi85!
I'm not sure whether I understand properly, but it seems you need to acquire data whenever you switch to different accelerometer, or by other words, when you switch input of your MUX (multiplexer). If this is the case, than what you are looking for is using analog input with external AI Sample Clock.
But first of all, I have to say at least 2 thinks - the product you have choosen is realy not the best for measuring signal from accelerometers (and who knows what you will have from the real vibration signal after you run it trough multiplexer ). Try to see what products you can find under products dedicated for vibration and noise measurement - DSA! Those boards have many advanages compared to m series when measuring vibration - start with dynamic range, go to dedicated converters for each input, oversampling, and so on... In fact, programming, however, is very similar (if not the same).
I'm not sure if I help you with matlab itself, but what as I mentioned, you are looking for using external sample clock. See M-series user manual, part with Analog Input Timing Signals, page 4-25. External sample clock signal can be taken from whichever PFI line.
What I found out is, that you can already use pfi routing with Data Acquisition Toolbox, what was not possible in the past. I recomend you to read Data Acquisition Toolbox User's Guide. Focus on chapter 17, as it describes properties.
Moreover, I'm not sure if this is not question stright for techsupport from Mathworks, as if i'm right, you are using all tools from Mathworks.
Even though I didn't come with explicit example, I hope it helped 😉
Regards,
Stefo
Thanks for quick response!
That is the situation..
I used P0.0 & P0.1 pins for Digital Output in the file with ''putvalue'' & ''pause'' commands, but maximum frequency that i reached was 70hz, which is not more...
I will test with two PFI pins 🙂
So, I have to set PFI0 = 0 and PFI1 = 0 i.e. [0 0] to output X voltage with multiplexer.
[0 1] for Y output, [1 0] for the Z output ...
How do I set up triggers for analog input?
For example, this is function for multiplexer with parameter "comb", whos is 2x1 vector...
-----------------------------------------------------------------------------------------
function mux_control(comb) %comb=[0 0], [0 1]...
dio = digitalio('nidaq','Dev2');
addline(dio,8:9,'out',{'line1','line2'}); % 8 & 9 must be PFI0 & PFI1 on port1
putvalue(dio.Line(1:2),comb);
% pause(0.001)
% propinfo(dio)
% getvalue(dio)
delete(dio)
clear dio
-----------------------------------------------------------------------------------------
Stefo if I understood correctly I must set these options on "ai"
set(AI,'TriggerType','HwDigital');
set(AI,'HwDigitalTriggerSource','PFI0');
but for Digital Output i am using PFI0 & PFI1 (both at once).
How to set up the trigger so that every time i call "putvalue" ([0 0] [0 1] or [1 0]) to start the trigger?
Purpose is to record each value of X, Y, Z in a file 😞
Regards, Krasi
- last edited on by
Content Cleaner
Hi Krasi,
thanks for perfect detailed explanation of your task 
How do I set up triggers for analog input?
-----------------------------------------------
In general, you can't use 2 signals as trigger or clock (you can in fpga, for example). You have to create one signal out of them to drive your trigger.
However, since you are generating those signals, then what you could do is to use one more PFI line, where you would generate one pulse (Logic High followed by logic Low) each time you want to switch input of the MUX (A,B / PFI0, PFI1). Let's assume you will generate this pulse on PFI2 (dont forget it has to be a pulse High-Low, since you are interested in edges).
Stefo if I understood correctly I must set these options on "ai"
set(AI,'TriggerType','HwDigital');
set(AI,'HwDigitalTriggerSource','PFI0');
--------------------------------------------------
I think you are right in this part (i'm not familiar with Matlab, but from documentation it looks you understand properly). From what we assuemd above I would just use PFI2 as HwDigitalTriggerSource.
One very important think to note is that you will create task starting at digital trigger - but just once! If you need to retrigger, you need to either restart task (the simplest) or you can use some more advanced, counter based retrigger. There is many resources on how to implement it in DAQmx:
Retriggerable Analog Acquisition in NI-DAQmx
However, if timing is not as essential (i saw you want to use software timed digital outputs), I would maybe go for the easier method (usualy I'm against, but ... easy is easy)
Regards,
Stefo
Okkkk, this is the new situation
I stil don't know frequency of sample rate of input signal
I write new functions.
The first is for PFI0 & PFI1 Outputs:
---------------------------------------------------------------------------------------------
function DIO_PFI0_1(comb)
DIO = digitalio('nidaq','Dev2'); %simulationn device NI-6255 on DAQMX software
Lines_1 = addline(DIO,0:1,1,'Out'); % add PFI0 & PFI1 on port1 as output
putvalue(Lines_1,comb); %output X
getvalue(DIO)
end
---------------------------------------------------------------------------------------------
The second is for PFI2 trigger output:
---------------------------------------------------------------------------------------------
function DIO_PFI2
DIO = digitalio('nidaq','Dev2'); %simulationn device NI-6255 on DAQMX software
Lines_2 = addline(DIO,2,1,'Out'); % add PFI2 on port1 as output which will be used for ai triggering
while(1)
putvalue(Lines_2, 1); %put values "1" and "0" without pause to simulate i.e fastest way i suppose!
getvalue(DIO) %one pulse (Logic High followed by logic Low)
pause(1)
putvalue(Lines_2, 0);
getvalue(DIO)
pause(1)
end
---------------------------------------------------------------------------------------------
---------------------------------------------------------------------------------------------
while (1) % switch PFIO and PFI1
DIO_PFI0_1([0 0]);
pause(1)
DIO_PFI0_1([0 1]);
pause(1)
DIO_PFI0_1([1 0]);
pause(1)
DIO_PFI2
end
while (1)
DIO_PFI2 % i don't know where to put this but obviously is not here !
end
---------------------------------------------------------------------------------------------
Since the cycle is endless i can not switch both functions simultaneously 😞
My question is how to start both together so I set them to pause's (for PFI2 it will be a less according to the picture)?
Regards,
Krasi
Hi there and Happy New Year ! 🙂
At this stage, after i using pins P0 or PFI as pulse generator can not achieve a switching frequency more then 100HZ because it uses software clock!
- pointer mouse on pictures for more information
the code is this:
DIO = digitalio('nidaq','Dev1');
Lines_1 = addline(DIO,0:1,1,'Out',{'line1','line2'}); % add PFI0 & PFI1 on port1 as output,
Lines_2 = addline(DIO,2,1,'Out','line3'); % add PFI2 on port1 as output which will be used for ai triggering
% line1,2,3 are names of PFI0, PFI2 & PFI2
while(1)
putvalue(Lines_1, [1 1]);
putvalue(Lines_2, 1);
putvalue(Lines_2, 0);
putvalue(Lines_1, [0 0]);
putvalue(Lines_2, 1);
putvalue(Lines_2, 0);
with no pause between commands have a delay 😞
Can I use both on-board counters (ctr0 & ctr1) and output "freqout", i.e. ctr0 & ctr1 should be control signals for multiplexers and "freqout" be used as "HwTrigger" for analog input.
Is there a way to reach onboard counters in Matlab build-in functions or only with NIDAQ-mx functions?
I attach a file with what I found for Matlab & NIDAQmx functions..
Please help me, i am new in Matlab and this things but deadline for project is comming! 😞
With greetings, Krasi
