Generating a PWM using USB 6008

[Subodh]

Thanx Mike...I will try it out. It would be great if I could have the vi compatible in Labview 7.0.

Subodh

[MickeyD]

Hi Subdoh,

Sorry about that I forgot you were using 7.0. This one is saved for 7.0. Please let me know if you have any further issues.

Have a great weekend,

Michael

[karim84]

hi subodh,
i'm also doing the same project and have to use the PWM to control the speed of my car. Could you please tell me how you did or send me a copy of your VI because mine doesn't work well.

thanks for ur help.

[ChinJohn]

USB 6008 support count at 5 MHz, that means USB communication speed is faster enough for this PWM case.

From  Jeff  VI code, each 1ms only upload 1 point, so speed is only 10 Hz.

But if upload 1000 points (10 loops), then  PWM speed increase to 10 kHz ( 0.1ms)?

 

USB 6008 not with me now, I will test it next week and feedback result.

 

 

[Dennis_Knutson]

The 6008 doe not support a counter output at all, let alone one at 5MHz. It has a counter input only - read the specs again.

Read the entire post again as well. The only outputs you have on the 6008 are software timed. You cannot get close to 10 kHz with software timing.

[RT4CY]

Hi ChinJohn,

Dennis is absolutely correct.  The USB-6008 has only one counter, which is marked on the device as PFI0.  Another thing to note is that it only has a source (no gate).  Thus, you can only use this counter to count edges.  For PWM, please consider one of our M-series boards such as the PCI-6221.  If this is not an option, you can do a software-timed PWM using the digital lines.  Keep in mind this is software-timed, so make sure that your application does not require high precision timing.  For an example on how to do software-timed PWM, please see the following article.

Software-Timed PWM Using a Digital Output Line

[ChinJohn]

Here is some missunderstand.

5 MHz is input counter speed, it proves the capability of USB comminication in USB-6008.

The datasheet marks USB-6008 speed as 48 kS/s, but not has specifically for the Digital Ouput rate. 

If software timed limit at 1kHz one digital smaple, how 5 MHz and 48 kS/s come from?

M-series boards is full support PWM is ok,  but if  someone only need one simple PWM test, there are more powerful, easy and cheap products than it.

Message Edited by ChinJohn on 10-13-2008 09:46 PM

[Dennis_Knutson]

The 5MHz and 48kS/s are for the counter input and for the analog input - as stated on the specs. These are separate circuits. The analog out and the digital I/O circuits have no connections to a hardware timing source. That is why they are both software timed only.

As already mentioned, the 6008 is a poor choice for PWM and that is not what it was designed for.

[RT4CY]

Hey ChinJohn,

Dennis is correct, and I just wanted to clear up a few things.  The data sheet you are referring to actually includes both the USB-6008 AND USB-6009.  The 48 kS/s refers to the maximum analog input samping rate of the USB-6009.  The USB-6008 is limited to 10 kS/s.  Just to drive the point home, here are a couple things to keep in mind.

1.  You cannot do a hardware-timed PWM with the USB-6008/6009.  A hardware-timed PWM requires two counters to generate a pulse train. You can only use the counter on the USB-6008/6009 to count edges.  The maximum rate at which the USB-6008/6009 can count edges is 5 MHz.  Please consider one of our low-cost M-series devices such as the PCI-6221 for a hardware-timed PWM.

2.  Again, 48 kS/s refers to analog input.  Additionally, this refers to the USB-6009.  The maximum sampling rate of the USB-6008 is 10 kS/s.

Please also understand that the USB-6008/6009 were intended to be used for very simple DAQ applications.  You will notice that Analog Output and Digital I/O are both software-timed.  This means that these functions will be completely dependent on your computer (how fast it is, how much memory, etc.).  If you need to do more than just very basic DAQ (such as a hardware-timed PWM), please consider our M-series devices.

Let me know if anything I mentioned is unclear.  I'm here to help.