where is the output for PWM on NI 7774 connected to motion control card 7356

[simitci]

Hi,

I have NI motion control card 7356 which interfaced through 7774 interface board. PWM outputs are written to be on pins 5 and 9 on Digital IO, yet there is no indication about the whereabouts of these PWMs on the interface board (7774). Would you please help???

Asst. Prof. Vasfi Emre Omurlu, Ph.D.

[Jochen]

Simitci,

For the digital I/Os a UMI-7774 provides access to 16 digital lines. If you want to access other signals of the digital connector, you shouldn't connect it to the UMI but to another breakout box like the SCB-68. Please note that compared to the UMI-7774 the SCB-68 doesn't provide optical isolation or 24 V connectivity. If this doesn't work for you, you could think of building a customized cable that connects the lines for the16 digital I/Os to the UMI and the rest of the signals to another connector or breakout box.

You also should be aware of the fact that the PWM outputs of 73xx boards are static. That means that you can change the duty cycle and output frequency of these signals in software only, which is quite slow. In most cases these PWM signals can't be used for motion control tasks.

What do you intend to do with the PWM signals?

Thanks and kind regards,

Jochen Klier
National Instruments

[simitci]

Hi,

Thanks for the quick response. I will be using the signal to drive the DC motor of a model helicopter in order to find its frequency response. The motor driver accepts 100 Hz constant frequency PWM and 10->20 % duty cycle in order to get min and max speed respectively. I will be changing the duty cycle in a certain frequency bandwidth like 0->200 Hz so that I can drive the motor with white noise like signal.
🙂

Thanks for your help and time...

[Jochen]

Hi,

I don't have the feeling that the PWM outputs of the 7356 will meet your requirements. As already said, you can change the duty cycle only in software and this will be typically too slow for your application. I think a better option would be a simple multifunction DAQ board like the PCI-6220. This board provides digital outputs that can output digital patterns with a data rate of 1 MHz. This should provide enough timing resolution and accuracy for your application.

Jochen