In my misspent youth I found myself doing clinical rotations at a local hospital. My fellow students and I were the lowest of the low on the hospital pecking order, being the ones doing the bulk of the work in the department and paying for the privilege to do so. As such, our locker facilities were somewhat subpar: a corner of a closet behind a door labeled “COMMS”.
In the room was a broken chair and a couple of hooks on the wall for our coats, along with an intriguing (to me) electrical panel. It had a series of rectangular blocks with pins projecting from it. Each block had a thick cable with many pairs of thin, colorful wires fanned out and neatly connected to the left side, and a rats nest of blue and white wires along the right side. We were told not to touch the board. I touched it nonetheless.
I would later learn that these were Type 66 punchdown blocks for the department’s phone system, and I’d end up using quite a few of them over my hacking life. Punchdown connectors were a staple of both private and public telco physical plants for decades, and belong to a class of electrical connections called insulation displacement connections, or IDC. We’ve recently looked at how crimp connections work, and what exactly is going on inside a solder joint. I thought it might be nice to round things out with a little bit about the workings of IDC.
Continue reading “Punching it Down: Insulation Displacement Connectors”
I had a friend who was an electronics assembly tech for a big defense contractor. He was a production floor guy who had a chip on his shoulder for the engineers with their fancy book-learnin’ who couldn’t figure out the simplest problems. He claimed that one assembly wasn’t passing QC and a bunch of the guys in ties couldn’t figure it out. He sidled up to assess the situation and delivered his two-word diagnosis: “Bad crimp.” The dodgy connector was re-worked and the assembly passed, much to the chagrin of the guys in the short-sleeved shirts.
Aside from the object lesson in experience sometimes trumping education, I always wondered about that “bad crimp” proclamation. What could go wrong with a crimp to so subtly futz with a circuit that engineers were baffled? How is it that we can rely on such a simple technology to wire up so much of the modern world? What exactly is going on inside a crimped connection anyway?
Continue reading “Good in a Pinch: The Physics of Crimped Connections”
Putting crimp connectors on wires is one of the most tedious things you’ll do. It’s not easy, either, unless you have some practice. Before you start digging in to a pile of connectors, crimp terminals, and wire, it’s a good idea to know what you’re getting into and Gogo:tronics has a great tutorial on how to crimp electronics connectors.
Crimping connectors onto wires requires the right tool, and the most important for this task is – surprise – the crimping pliers. These pliers press the crimping wings of the connector into each other, a task made much easier on the non-ratcheting pliers if you use a rubber band to hold the jaws of the crimping pliers open just enough to hold a crimp connector.
The general theory for crimping all types of connectors is to strip a little bit of insulation off the wire. Then, put the connector into a suitably sized space in the jaws, insert the wire, and crimp it down. For non-ratcheting pliers, it’s suggested the connector be re-crimped with the next smallest hole in the jaws.
There are a few connector-specific tips for the most common connector types, too. Dupont connectors – those flat, black connectors with a 0.1″ pitch – go together like you think they would, but for larger connectors – VH and XH-style – it’s important to use the right wire gauge and not to squish the square female part of the connector.
Etching and populating a board is childs play compared to finding connectors which link several components. But Hackaday alum [Ian Lesnet] and his crew over at Dangerous Prototypes have come up with a solution that makes us wonder why we haven’t seen this long ago? They’re prepping an any-size ribbon cable kit.
So lets say you do find the type of connector you want. You need to cut the ribbon cable to length, crimp on the connectors, then seat those connectors in the housing. We’ve done this many times, and being cheapskates we use needle-nose pliers instead of buying a proper crimper. This solution does away with that grunt work. The kit will ship several different lengths of ribbon wire with the connectors already placed by machine. This way you peel off the number of connectors you need, select the proper house size and plunk it in place. Also in the kit are several lengths of male, female, and male/female jumper cables you can peel off in the same way.
Now what are we going to do with the rest of the spool of ribbon cable sitting in the workshop?