|Re: HP-IL over Cat5 - Compatible?|
Message #14 Posted by Howard Owen on 26 Aug 2005, 1:44 p.m.,
in response to message #1 by Howard Owen
Well, it works.
To all you hard core EE types, let me just say, I'm glad you're here. I'm a software guy. I figured it would be fun and interesting to hack on hardware as a hobby. But I lack skills in that area. Now, I'm not talking board design or anything like that. I'm talking basic electronic tech manual skills, like soldering. I've actually gotten fairly OK for crude work, once I got myself a temprature controlled iron and figured out that it has to be really hot to do any good. But I still appreciate the help and input I get from the more experienced folks here.
I happen to have a spool of Cat5 here in my work cabinet. That, and the fact that the specified impedence of Cat5 matches the HP-IL's spec, and that for lengths over 10 meters, that same spec calls for twisted pair are what motivated me to consider this approach. Don's warnings regarding the problem of mating the solid core Cat5 wire with the stranded HP-IL cable gave me pause, however. So I figured I'd solder decapitated HP-IL connectors onto Cat5 cable, and cover them with shrink wrap in an attempt to protect the awkward mechanical mating of the dissimilar wires. Through trial and error, I found that the following process worked pretty well:
- Cut the heads off an HP-IL cable. (This is one of those "puckering" moments for an inexperienced electronic tech who is jumping into the unknown!)
- Strip about 3/4" off the ends of a CAT5 pair and both wires of one end of the decapitated HP-IL cable.
- If this isn't your first end, mate the other end of the HP-IL to the one you are about to solder. This makes it easier to be sure you solder the right wires.
- Mount the wires to be soldered in some sort of frame. I use one of those el-cheapo soldering stations with the magnifying glass and alligator clips on rails. I remove the glass (since I use a larger illuminated one) and put each end of the work into one of a pair of clips. On the HP-IL side, the hard plastic connectors are a good place to appy the clip. On the Cat5 side, the cable itself is OK.
- If this isn't your first end, check the end you already did to see which one of the Cat5 wires to solder to which HP-IL cable. The connections should be "straight through" as the mated cables will show.
- Cut a two inch piece of 3/16" shronk wrap tubing and pass the Cat5 pair through it.
- cut two one inch sections of 1/16" shrink wrap and thread one of the wires through each.
- The bundle of shrink wrap should be able to move at least an inch away from the work, because you are about to apply lots of heat there. 8)
- Maneuver the stripped ends so that they overlap each other on the same plane
- Bend the Cat5 wire around the HP-IL wire. This is the opposite of what the wires "want" to do. The reason is, the solid core Cat5 wire will retain its shape, which the soft HP-IL cable will conform to. This means that it will stay in place, which allows you to solder with both hands free.
- Make only two to three revolutions around the HP-IL cable depending on the length of the stripped wire. This makes a nice flat arc to place the soldering iron tip on.
- Heat your iron to above 600 degrees, Fahrenheit. I use 640. Tin the iron.
- Place the soldering tip underneath the arc of the entwined wires at one end of the arc.
- Count to three, moderately slowly
- Apply the solder to the top of the wires, above where the iron is placed. It should immediately melt.
- draw the iron along the underside of the wire bundle while dragging the (shortening line of) solder along the top.
- Remove the iron and solder from the work.
- After cooling and inspection, trim off excess wire at both ends of the new join.
- If this is your second connector, you have reached your earliest opportunity to test the cable. If you find a problem here, you'll save youself some work compared with finding it later. Test continuity through both conductors. You got the right ones? Good. Be sure the cable doesn't short at either end and plug it in to a test bed. I used EMU71 running on a PC to CAT a real 9114 on a loop that included my cable.
- Slide the small shrink wrap sections over the soldered wires and heat them until snug. (I use a cheap heat gun which works a lot better than the iron.)
- If you don't get all the conductor covered with the shrink wrap (oops) dress it with electrician's tape.
- Slide the larger shrink wrap over the two wrapped joins and shrink it into place.
- Test the cable again!
- You probably want to HP-IL out and back with the same cable. If so, do a second pair like the first on the same cable. (But with the gender switched, of course. You should have both a male and a female HP-IL connector at each end.)
And it works with about a 45' cable!
But that joint is still brittle. The shrinkwrap doesn't seem to do the trick. The stress occurs in the Cat5 copper just on the edge of the solder joint. Any ideas?
Update: It was brittle while I was trying to appy the shrink wrap. After I got that applied, I had no further trouble. It's undoubtedly still brittle, but protected somewhat by the plastic tubing. A radical bend at the end of the solder joint could still ruin my whole day, so I'm careful with it.
Edited: 26 Aug 2005, 8:56 p.m. after one or more responses were posted