Hi all - On Sat, 24 Apr 2004 Charles Poole <pochas@...> wrote: > I would like to provide a TTL level analog signal to external device by > sending data through a USB port then converting to analog. What hardware > interface might accomplish this economically and how would I go about > setting up a software interface with an FB program? > > I have a pressure sensor, a PIC microprocessor, and a LCD display hooked up > and working. > I now need to simulate a variety of time-varying pressure profiles to debug > the micro program. > The micro program was developed on a Windows machine using Microchip > software but the software can't supply the realistically varying inputs that > I need. > > If anyone has had to deal with this, I would sure like some help as trying > to become a USB > driver expert would be a show-stopper for me. Robert Covington suggested the 'IO-Warrior' as a possibility, and from looking at the data sheet this looks to be a neat device. Since I'm not sure how to talk to it from FB, and since it would need the addition of a DA convertor, I would probably go in a slightly different direction. Since even an inexpensive ($2) PIC such as the 16F627 includes a USART and a PWM output, I would use one of these along with a USB to serial convertor such as the Keyspan USA28X. The serial support in FB works well, and the PICs PWM output is capable of 8 to 10 bits of resolution, which when fed thru a suitable low pass filter provides a nice DC Control signal (I have done this many times). The serial protocol could be as simple as sending a byte out that would set the PWM output to that 8 bit value, and using a 4 MHz crystal for the PIC would produce a PWM cycle rate of 4 kHz that would call for a 400Hz or so LPF and produce an update rate as t least as fast as the 'IO-Warrior'. I have been using PICs to implement data collection and device control via the MACs serial port for many years now, and FB is a wonderful language to write the control programs in. I also use the MAC to write, assemble, and load the firmware into the PIC (albeit under Windoze running on Virtual PC). I much appreciate this mailing list as source of inspiration, and also a connection to the FB community, and I would be happy to supply more design details if anyone is interested. Best, Walter -- =========================================== Walter Lenk Cambridge Ma 617-547-7781 ===========================================