Newbie needs help with PWM, DAQ, good reference guides, and life

[Kevin_Price]

Tobias,

Do you mean that you want both counter outputs to change freq and/or duty cycle simultaneously? And to always be equal to one another? If so, why have two rather than one?

On the other hand, if you want your two counter output freqs and/or duty cycles to be variable and different based on the result of control algorithms, I can't understand what you would mean about having them synchronized. It seems that they couldn't be both independent and synchronized. Exactly what aspect of synchronization do you mean?

Can you describe your app and the function of these 2 counter outputs in more detail? Also, what type of data acq board(s) do you have available?

-Kevin P.

[Tobias]

Hello Kevin,

glad you want to help me. I have attached a worddokument that describes the problem.
The application has to control power in an induction hob system controlling two IGBTs in a halfbridge. The two IGBTs mustn't switch on at the same time. There has to be a delay of 2µs between transition of Puls1 from hight to low before Puls2 goes from low to high. This delay is constant 2µs.
But the Frequency of the Pulses has to be changed.

[Eric]

Okay things are starting to fall into place, which only means I am going to have many questions in the new few days. Here is a stupid question that I need answered. How do I take a data input and simply divid it by a decimal number. I tried just using the basic two input divide block, but the numeric constant wont allow a decimal number. When I increase the precision of the constant it just shows me that many more zeros after the number after it rounds 45.235 to 45.000. What am I doing wrong?

Thanks again for putting up with the newbie

Eric

[Dennis_Knutson]

Is the color of your numeric constant blue or orange? If it's blue, then you've created an integer constant. Simply right click on it and select Representation and change it to DBL.

[Eric]

Hello All,

This email is not about LabVIEW but I thought someone out there might be able to help me.

We just hit a major setback. The guy in charge of ordering the motor driver got one that was too big for our little 6V motor. Now we need to find one to order very very soon. I have terribly little experience with motors and motor drivers. Does anyone know of any motor drivers that will accept a PWM signal and drive a 6V motor backwards and forwards. I need six pins: Supply voltage,PWM, Direction, GND, Motor terminal A and motor Terminal B. Any help would be greatly appreciated.

Much thanks from the U of A

Eric
The search continues...

[MarcoPolo5]

Eric,

You are definitely on the right track with using either Analog Outs or Digital Outs. The M-Series MIO boards have the capability for outputting an analog waveform at 833kS/s and correlated DIO at up to 1MHz. If you use DIO, you would have to set up a 'dummy' continuously running analog input or output code with which to 'correlate' the hardware timed DIO output. You can not directly set an output clock for hardware timed DIO.

Here is a link to a correlated DIO example:
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=E4C68BB4D82A126DE034080020E74861&p_node=201229&p_source=External

If you are getting a triangle wave on your analog output using the Square Waveform.vi, it is likely that you are not setting the sampling info settings high enough.

I included a simple example that builds up an array that simulates PWM. You could try this with a continuous Analog Output or Correlated DIO - and continuously write new data to the output vi.

Good luck with your project!

[MarcoPolo5]

Eric,

You could look at National Instruments Drive Advisor, however, there are really no solutions for very small DC motors.
http://www.ni.com/devzone/advisors/motion/driveadvisor.htm

How much current is your motor rated for? You might even consider a small custom amplifier circuit (depending on your circuit design skills) that could take PWM or Analog input. The following link has some examples. Hope this helps:
http://www.electhai.com/E_link/Link_Motor.htm

You might want to look at small robot motor controllers - they normally can take PWM inputs. Most H-Bridge configurations (without attached controllers) can.

http://www.robotstore.com/catalog/list.asp?cid=17

Good luck with your project!