T&L Publications

Hi, <p>I am new to this board and hoping to find some information on controling my robot through the USB port. As the USB port can handle 127 devices at once, this should be more than needed for my Robot.<p>My first task is to replace the joystick pots on a wheelchair motor controler with digital pot's. What I need is to learn how to connect and control Digital Poteniometers with a UBS port.<p>I understand this might be a big task, I do not want to buy boards that cost $50 to $1000 for each item. I would like to build as much as possable from scrach, that way I will learn more and save money I hope.<p>I purchased a X9111TV14ND digital pot made by Dallas but it is not designed for USB, does that mater? can a circuit be built that can make it work with USB? Does anyone know of a Digital pot made for USB?<p>I am not an Engineer, but I am an Electronics Tech., But I went to school befor there were PC's.<p>I can see by some of the posts on this board that some very smart people answer posts here, I am hoping for some of them here.<p>Thanks much
w_kinne

USB to digital pots. This is actually multiple items: USB interface, digital pots, interface protocol (how your PC sw talks to the pots) and the PC SW. <p>There are lots of ways to interface to USB. Do you want to completely roll your own or buy prebuilt modules? You can get USB to serial converters reasonably cheaply - that may prove to be the simplest approach. Look through the pages of N&V or CCI for ads. If you are conversant with microcontrollers, Microchip has a bunch of apnotes on USB (though I've not looked at them).<p>You'll need to come up with a protocol for talking to the digital pots, probably via a microcontroller. For the pots, I think its simple - a value byte for each of the 2 (4?) pots on the virtual joystick. You might want to have more sophisticated commands like ramp from 0 to 255 (or what ever) over a certain period of time. If it we me doing it, I'd generalize the protocol so I could add additional object to command (motors and such) and support status read from the the device(s).<p>For digital pots, maxim and microchip have plenty of application notes. I'd take a look at several of the them to get an idea of how to procede. One thing to be aware of, digital pots can't dissipate much energy - like .05W or so. You might need to do a lot more than just replace the mechanical ones.

And I guess the primo question would be;
Are you well versed in either V-Basic or C++ , including port controls ?

I can program in C++, but I would not say that I am well versed. I do however go to church with one of the head programers for Dow Chemical who knows C++ and V-basic and he is willing to help me. I am willing to buy what I must but would like to build as much as possiable. It looks like buying a USB device to plug into my USB port is a must for me. I found some on the net but want to be sure I buy the right one. I have seen them for as little as $59 and as much as $1000. If I only have to buy one and can connect lots of devices to it then I'm happy. If I have to buy a $59 card for each digital pot I want to control, that would be unacceptable. I am reading everything I can get my hands on, Learning USB by doing, by John Hyde seems to be helping. I scan the internet and read anything that looks like it will help. Any direction at this would be most helpfull. USB Complete by Jan Axelson sold at her sight www.lvr.com looks like it might help but at almost $70 I would want to be sure it was worth it for what I am trying to do. Any feedback from people on this board would great.

I asked Micochip the same question about their USB PIC 18F4550 chips. They recommended getting its demo board at http://www.microchip.com/PICDEMUSBFS for $60.00. It has at 3 or more 8 bit I/O ports and 16 analog bits. They have lots of documentation. The flash memory is software programmable on USB. They are back ordered until 3/18/05 so I don’t have it yet but it looks like everything I will ever need. The chips are $6.00 but you only need a USB connector, 2 caps and a crystal to make them work.

Dave, the PIC Demo board schematics are in the user guide so you could probably put one together for cheap. There really doesn't apear to be much to it. I've done similar with other demo boards from microchip.<p>Phil<p>[ March 10, 2005: Message edited by: philba ]</p>

Vellman has a nice usb interface kit for about $50.00 and has some sample software. It has a couple of analog outputs and digital I/o.

Any updates?

I got the PICDEM FS USB board. On this CD the tutorial is for Borland C 6. Has anyone seen any samples or tutorials to communicate with that board / chip using Visual C++ 6.0? Microchip couldn't help. I have enough trouble learning and using Visual C and that is what all of my programs are in. What sort of changes do I have to make to Borland source code to convert it to Visual C++ and are their libraries compatible? If you know of a sample that would enumerate, set up a buffer and let me send and receive at full speed, it would really help and I can take it from there.
Dave

I found what I needed at http://forum.microchip.com/tm.asp?m=73062