Sending out a Pulse Train

[exavier45]

I need to create a PID controller in labView.  I need to ouput a signal that corresponds to a certain duty cycle to control the speed of a computer fan. 

So I need to create a signal at a ceratin freq. and  duty cycle  that corresponds to the switching of full power to no power of a fan.   The  signal needs to go through a  PID controller  inside labView and the signal needs to be sent out to a amplifier circuit that connects to the computer fan to vary the speed of the fan.  A three-wire fan will be used.  So i also need to send the tack signal back into labView to be proccessed in the PID controller  to adjust the error.

Is there any limitations to the type of PID controllers you can create in LabView?
The signal coming back into labView are there limits on the way it needs to be conditioned to get back into labView?
Also need to know how i can send this signal out of labView and is there any limitations on the type of signal i can send out?

We want to avoid buying a DAQ board so i would really like to do this serially with the com port or serial port.

[Dennis_Knutson]

The com port is the serial port and if you hope to send out a pulse train through this, you are not going to have a lot of success. First, the serial port will output +/- 15 volts, the data will include start and stop bits, and it will get clocked out at the baud rate for the port. You would have better luck using the parallel port and one of it's data pins but you will still have a hard accurately controlling the frequency of the signal. The best you can hope for is a 1msec resolution and even that will vary depending on other tasks the OS might decide to do.

[exavier45]

a thousand hertz would probably be sufficient frequncy for my application.  But i think i am going to go the microcontorller root and just send the signals staright into labVIew to record the data.  thanks.