DRO Hardware Page

DRO+ Hardware

Well, I finally got around to making some headway here, and I think you'll all be happy with the route I took. I really wanted to do the full-blown motion control card, 3-4 axis, digital and analog I/O, and PWM amplifiers, but I figured this was major overkill for the average guy. So, I backed off to the point that would cover what most people want - a simple DRO, so only input was required, no complex current-to-voltage circuitry needed for motor control, and most importantly, the major part was a single IC. Much cheaper, much easier, and more to the point. If there's outcry for the bells and whistles card, I can do that later. I probably will anyway, although it won't get a web writeup without interest from outside.

Now, on to the guts of it! You're probably wondering if this is a project you can handle. Let me tell you, if you don't mind moving slowly, checking your work for mistakes, and being patient, this is a cakewalk. I don't require that you have a degree in electrical engineering. I'm going to lay this out by the numbers, as straightforward as I can. Along the way, I'll add what comments I deem necessary, and links to detailed descriptions of the inner workings of the card and of your PC. With luck, you'll have a DRO *and* a good understanding of basic PC bus architecture when it's all over.

First, the parts. Below is a list of vendors and the required parts available from each. There may be better places to buy this stuff, but you can trust these, since I got the parts from the same places. Feel free to price hunt or scrounge out of junk boxes you might have, but unless you're knowledgeable about substitutions, don't get too crazy. You're not going to save all that much time or money.

U.S. Digital:
      Website: http://www.usdigital.com (no online ordering)
      Phone (Sales): (800) 736-0194
      Open 7:00AM - 5:00PM Pacific Time, M-Th
               7:00AM - 2:00PM Pacific Time, F
      Also a good source for encoders (rotary and linear)

      (1) PN: LS7266R1 (quantity 1)
            Desc.: Dual encoder to microprocessor interface chip
            Price: 22.50

Digikey:
      Website: http://www.digikey.com (online ordering available)
      Phone: (800) 344-4539
      Open 7:30AM - 11:00PM Central time, M-F
      Sells *everything* electronic, pricey compared to some, but almost always in
      stock

      *(1) PN: K104-ND (quantity 1)
            Desc.: Wirewrap/unwrap tool, regular wrap style, 30AWG
            Price: 21.00

      (2) PN: K225-ND (quantity 1)
            Desc.: Single wire dispenser, white wire, 30AWG
            Price: 11.75

      (3) PN: DM74LS138N-ND (quantity 2)
            Desc.: 74LS138 3-8 decoder chip
            Price: 0.74 each

      (4) PN: V1071-ND (quantity 1)
            Desc.: T44 Miniwrap terminal (100 per pkg.)
            Price: 6.34

      (5) PN: ED4316-ND (quantity 2)
            Desc.: Wirewrap 16 pin IC socket
            Price: 1.83

      (6) PN: ED4628-ND (quantity 1)
            Desc.: Wirewrap 28 pin IC socket
            Price: 3.20

* This is a tool, not a part. If you can borrow one, do it.

Marlin P. Jones and Associates
      Website: http://www.mpja.com (no online ordering)
      Phone: (800) 652-6733
      Open 9:00AM - 4:30PM Eastern, M-F
      Great junkpile to dig through, check out the website, get the catalog

      (1) PN: 9003PB (quantity 1)
            Desc.: 8-bit ISA project board
            Price: 7.95

      (2) PN: 0339-CD (quantity 1)
            Desc.: .01uF ceramic disc capacitor (15 per pkg)
            Price: 1.00 each

      (3) PN: 5688-PL (quantity 1)
            Desc.: DB-25 connector (female)
            Price: 0.50

      (4) PN: 11451-CB (quantity 1)
            Desc.: DB-25 connector cable (male-female)
            Price: 3.95

OK, so that comes to... 63 bucks, give or take, plus shipping. Another 20 bucks for the wirewrap tool if you can't borrow one, will set you back about 95 bucks total. Kinda higher than I wanted, but not too bad. We'll also need encoders, either linear or rotary, but that's a whole other can 'o worms. Best bet right now is 2 bucks per inch, and 30 bucks each for 2 encoder heads gives you linear (read: accurate) scales for under $150 ($60 for the heads, plus 25"x10" travel means 35" of encoders for $90. I figure that's the biggest mill that'll ever see this setup). If you don't like building covers for the scales, you can buy covered ones, but you'll pay for 'em.

I'm assuming that everyone either has, or can borrow, a soldering iron. If not, they're available in so many places that it doesn't bear mentioning. There isn't very much soldering anyway.

Please remember that the above parts will build a card which will support a 2-axis DRO. That's the level that most users really need, and there's no reason that most of the parts can't be re-used in a 4- or 6-axis version. The biggest difference is cost and time spent wiring.

Once you've got the parts, you should spend some time looking over some resources that deal with this subject. For wirewrapping, I've found two interesting things to read. First, there's a description of what you should do, and second, what you should NOT do. Also, look at:

http://www.cybercom.net/~ahvezda/hardware/misc/wirewrap.txt
http://www.boondog.com/tutorials/8255/8255.htm
http://www.engr.unl.edu/eeshop/proto.html
http://www.kent.net/~boucher/
http://homepages.wwc.edu/staff/stirra/engr/prototyp.htm

For some really good tips, including the 'skinny wire-wrap method', read the input from fellow RCM'er Dale Grover by clicking here.

These are all good sites for info about prototyping, wirewrapping, and electronics in general. There are zillions of other sites on the net, so have a look and get a feel for the hobby. It's not quite as expensive as metalworking is, and takes up less space. Blends nicely when doing those projects that have a mish-mash of skill requirements (robotics comes to mind).

Now, move along to the schematic page.