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NI USB-6501

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Hi there, 

 

Could some one give me some information about whether it is possible to use the 

NI USB-6501

 

As a PWM generator to control the Dimming function of 18 LED power supplies? 

timing it is not so relevant and if the pulse width could be controlled in the PC application itself the purpose would be met

 

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Accepted by topic author ONavarro

Hello ONavarro,

 

Technically it is possible, but please note that USB-6501 as only software clocked digital I/O (static IO). This means the periodocity ant the duty cycle of the PWM you want generate will be determined by a software loop, so dependant of you system and the USB bus. I think you will not be able to get a better loop rate (ability to change the state of a digital line) less than few milliseconds (system dependant).

 

For example, if the loop runs at 5ms, and I want 10 steps in my PWM, this means the period will be 50ms, so a base frequency of 20Hz. If you can reach 1ms, you'll get 100Hz. If you want more than 10 duty cycle value, you will have to lower the frequency.

 

And this will NOT be stable (software loop at 5ms, first delta 5.8ms, then 4.9ms, 5.1ms, 6.7ms, and so on), because it relies on software. If you need someting stable and/or faster, choose a device with hardware clocking.

 

Best regards,

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Hi Mathieu,

 

Thank you very much for replying 🙂 

I was afraid that was the case but it is okay since 1. Timing is not so important 2. Stability is also not important 

The aim is to be able to controll the LED supplies at a low rate e.g. 1Hz

 

Kind regards,

Oscar Navarro

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