Best Student DAQ For Pulse Width mModulation

[Greg Flynn 01]

Hi All

Can anyone advise me which of the following DAQs are best suited for Pulse Width Modulation

NI myDAQ

NI 6008 USB DAQ

I am a student and these DAQs are recommended by my college as they are reasonable to buy.

I intend running a 12 volt stepper motor using PWM

Thanks in Advance

Greg

[johnsold]

Greg,

I am not familiar with the myDAQ, but I can tell you that the USB-6008 is NOT suitable for PWM.  The digital outputs are software timed and the maximum data rate is less than 150 Hz.

Since you are a student, I recommend that you look up the data sheets and specifications for both devices and read them carefully to determine the suitability for your application.  If the myDAQ is also not suitable, then you can use what you have learned to search for a better device.

Lynn

[Greg Flynn 01]

Lynn

The myDAQ is also software timed. The max counting and pulse generation frequency is 100MHz (is this the data rate)

myDAQ specs http://www.ni.com/pdf/manuals/373060a.pdf

Greg

[johnsold]

It looks as though the analog output might be useful for PWM.  Look at the ELVIS Function Generator VI as a starting point.

The Digital Outputs are not suitable, as in the USB-6008.

Lynn

[bstreiff]

The digital outputs on both the myDAQ and 6008 are software-timed, but unlike the 6009 the myDAQ does support pulse output (up to 1MHz) to a single terminal using a counter; see the 'Digital I/O and Counters/Timers' section in the above-linked PDF.

The LabVIEW example Gen Dig Pulse Train-Continuous.vi demonstrates how to use this functionality.

[SnowMule]

Does it have to be corntrolled right from the DAQ?  You can build a PWM controller from a 555 timer; the circuits are readily available on teh interwebs and the parts are inexpensive.  A 6008 + external controller's going to be cheaper and achieve the same result that just buying a $1000+ DAQ will do.  :dunno

[Larry.C]

Hello Greg Flynn,

As has already been mentioned it is possible to generate a PWM signal in various ways. A simple working method with 1 counter would be to create a hardware timed loop in which you have a square wave generator and a control to alter the pulse width.

On a separate note, the myDAQ system is by far the most modular system and if bought by a student through their university, it is by far the cheapest DAQ device (with the most bang for its buck).

I hope this helps you make a decision, if you require more information please do not hesitate to post again.

Regards,

[Greg Flynn 01]

Hi folks

I was planning to use the 'Simulate Signal' function and configure a digital signal and use a control to alter the pulse.

I dont understand what is meant by using 1 counter to create a hardware timed loop?

Is that what I described above?

Laurance, can you confirm if the myDAQ is suitable for me.

I have looked at several other DAQs, following a phone call to NI, but the cheapest recommended DAQ is €500. I can get the myDAQ for €150

Thanks for all the replies so far

Greg

[Larry.C]

Hi Greg,

If you are trying to generate a pulse with varying width to control a 12V stepper motor, I would definitely recommend getting a myDAQ as it is cheaper and can be used for many more projects you may encounter. What would have to be done is an amplification of the digital signal as the output voltage range of a myDAQ is +-5V. The reason I mentioned hardware timing is mainly for synchronisation when also acquiring data on the myDAQ at the same time (where you do not want a phase shift or sync problems between the output and input signals due to USB form factor) or with the use of triggers.

For simply controlling a motor it would be possible to use the following LabVIEW inbuilt example which can be found by going to help > Find LabVIEW Examples:

Browse : Hardware Input and Output > DAQmx > Digital Generation > Write Dig Chan.vi

If you would like to find some student community examples with the use of myDAQ I would advise taking a look here as there are many great projects showcasing what myDAQ and other systems can do.