Recommend low cost USB DAQ to output 1Hz - 250Hz independently on 8 digital I/O ports

[JPNaidu]

Hi,
Could anyone recommend a low cost USB DAQ to output 1Hz - 250Hz (Pulse) independently on 8 or more digital I/O ports.
Its important that I should be able to control the duty cycle(pulse width) and, I should have control over the pulse through each I/O port.
Thanks.
Naidu

[BrowningG]

Hello Naidu,

Thanks for contacting National Instruments. 

Since you would like to control the duty cycle for your pulse, I am assuming that you would like to use hardware timing for your output.  There are two options for performing continuous pulse generation. 

The first is to create a DAQmx counter output task and specify the frequency and duty cycle of the pulse.  To do this separately for 8 digital lines, a counter/timer board is required.  These are available only in a PCI and PXI form factor. 

The second option is to generate a digital waveform and use hardware timing.  The National Instruments website has many options for this and allows for you to narrow down your product selection by categories.  The Data Acquisition (DAQ) Hardware page is a great place to get started. The CompactDAQ page also has several digital input/output (DIO) modules that use hardware timing for waveform generation.  These devices will require a CompactDAQ 9172 chassis to operate. 

If you are interested in a particular module, please feel free to contact NI or from the product page select “Call me now!”  This option will have a National Instruments technical representative contact you to help you find the best possible solution for your needs. 

Please post back if you have any questions.  Have a great day!

[AAL]

Hello

I have a follow up question. What devices capable of outputting a continuous digital waveform or pulse generation (i.e for either option 1 or 2, as per NI's response) are available with USB interface? I have tried to call NI but there were unsure if this functionality is available under USB. Please advise.

Thank you

Regards

Albert

[AAL]

Any recommendations from NI?

Thank you

[margasan]

Hello AAL,

You may take a look at the NI USB-6341:

NI USB 6341

Or a cheaper solution will be the USB 6009, but it only has 1 counter

Regards,

Mart G

[Mcdan]

AAL,

In your original post, you mention needing 8 digital I/O ports.  Can you clarify what you mean by this?  In reading the rest of you post I got the idea that you needed 8 Digital I/O lines, each of which could output an independent signal.  Also, how independent do you need these outputs to be?  With most devices such as the USB 6341 Mart mentioned, there is a single digital I/O port which can be updated in a hardware timed manner.  The entire port must be updated on the same clock.  To get pulses of different frequencies on different lines (assuming 50% duty cycle), you'd then need to calculate a sample clock rate which is least common multiple of all frequencies times two.  You need to output and calculate your data to write accordingly.  For instance, if I needed to output a pulse of 3 Hz, 5 Hz, and 6 Hz I would need to update the port at a rate of 60 Hz.  You would then write the following data to the port (assume line0 = 3 Hz, line1 = 5 Hz, and line 2 = 6 Hz):

0,0,0,0,0,4,6,6,6,6,3,3,1,1,1,5,5,5,7,7,2,2,2,2,0,4,4,4,4,4,3,3,3,3,3,7,5,5,5,5,0,0,2,2,2,6,6,6,4,4,1,1,1,1,2,7,7,7,7,7

This data would then be repeated to continue generating these waveforms.

If all of this needs to be started/stopped or frequencies need to change throughout the run, this becomes much more difficult as all of the calculations necessary to do this would need to be done on the fly.

If you need to start/stop each line independently, and change the pulse characteristics as the generation is running counters are better suited to your task.  Unfortunately, I don't know of any USB device with 8 counters.  The USB-6341 has four counters, so two of these devices would meet your needs.

Note: the USB 6008 does not support hardware timed output, so it is not a good candidate for this type of generation.  Also, it's one counter supports only edge counting so this would not work as output generator.

If USB is not a firm requirement, then we do have several devices which may fit your needs.  We have counter/time devices such as the PCI-6602 which do have 8 independent counters, and we have products with reconfigurable I/O such as the PCI-7811 which may also suit your needs.

I hope I've understood what you need to do correctly.  If not, please let me know.

Dan

Edit: If you want to go the digital waveform route, you may also look at something like the cDAQ 9171with the NI 9401 module.