Skill: Custom Breadboard/Molex Connectors

Disclosure: There are both affiliate and direct links to some of the tools and consumables used in this project at the bottom of the post.

We connect a lot of things to a lot of other different things. When prototyping, we use breadboards. A wire salad may look pretty, but it’s hard to debug and diagnose problems: let’s clean some of that mess up by creating some custom connectors to keep things a little bit neater.

(Okay, this is a contrived example, but when we start adding multiple components on a full-size breadboard, it all starts to make sense. Trust us.)

As part of our upcoming Maker’s End Inspiration Series of books we’re going to be doing a lot of prototyping on breadboards. Since many of the parts will be the same across projects, we thought it might be cool to have some pre-made jumpers for some of those parts. So we made some!

We’ll turn some pins, wires, pin holders, and heat-shrink tubing into a cable that’s exactly what we need: a double-ended three-pin jumper.

We’ll also need the usual suspects of tools:

  • Wire cutter
  • Wire stripper
  • Crimper
  • Pliers (maybe two)
Tools used

The operation will proceed much as you’d expect (but we made a video anyway, because we’re chatty, and sometimes it’s more inspiring to hear someone blab on instead of just looking at some pictures.

The pins themselves vary by manufacturer. These pins looked to be press-stamped, so instead of a “pin” it’s actually more of a U-shaped “channel”. This isn’t ideal: we’d prefer a higher-quality actual pin. They’re easier on the breadboard, stronger, and just all-round more pleasant to work with. But these aren’t awful, and they get the job done.

When you look at the non-pin end of the pin you’ll see some flared triangles: they grab on to the insulation and keep the wire from coming out. They often come too flared, though: we sometimes “pre-process” the pins so they’ll grab the insulation a little easier (makes the crimp go easier) and actually fit into the crimping tool.

Fixing flared pin by squeezing it
Fixing flared pin by squeezing it

Each pin is inserted (once it’s attached to a wire) into a “receiver” (the chunky part of jumper cables) that look roughly like this (we’ll get a better image).

pin receiver, what the pins are inserted into
Pin receivers

Let’s wire one up. We’ll also wire up a single-pin jumper in parallel in case you’d like to try your hand at a less-complex attempt first, before jumping into a complete jumper: basically a breadboard jumper wire instead of a set of wires.

Step One

Cut the wires to whatever length you want your jumper to be. Note that if you want to “bundle” up the cables (as we’ve done here with bits of heat-shrink tubing) you may want to make the “inside” wires a bit shorter, but it’s not that important.

Step Two

Strip the wires so they’ll make contact with the pins. Every pin has its own specification for how much wire to strip; these particular pins were about 1/4″ or so, but we mostly just eyeballed it.

After stripping the wires you’ll need to twist them together, tightly, especially if you’re working with one of the super-flexible “crazy” wires, otherwise it’ll be difficult to seat the wire in the pin correctly.

Step Three

Lay the wire in the pin. The large “wings” on the back of the pin grip the insulation, keeping the wire in the pin. The electrical contact is made further up the pin by the next, smaller “wings”.

The wire should be inserted into the “channel” near the end of the pin. This ensures good contact (and is where the precision stripping comes in to play). It’s often easier to strip a little bit extra and trim to fit.

Step Four

Crimp it! The channel side should be in the “receiver” of the crimping tool: it has bends in it that force the “wings” down into the insulation and over the wire. It’s basically a stapler, where the pin is the staple, and the wire is the paper.

Just squeeze the handles to crimp.

If you see what’s in the image below, try to remove the wire and pin from the tool–here the wire has crept out of the pin; this will lead to a bad crimp, and poor (if any) connection, and the wire is likely to pull out.

shows the wire falling out of the pin right before crimping
The wire is falling out 🙁

Revel in your handiwork. The black wire was a good crimp, the red wire got inserted a bit, and some insulation has gotten into the connection area. When this happens the connection may or may not be solid (in this case it was).

Step Six

Once you have pinned all your wires they can be inserted into the connector. The connectors (usually) have a little arrow showing which direction to insert the pins. Sometimes the pins stop where they’re supposed to, sometimes they don’t.

We usually start them by hand, possibly nudging with a pair of pliers, then often (usually) need to pull them the rest of the way through by gripping the receiver with pliers, gripping the pin with pliers (gently, especially these cheap ones), and pulling until we see the “channel” part of the pin in the little window.

If you’re making a simple jumper wire you might want to add some heat shrink tubing. It provides a little bit of strain relieve, provides a handle to grab on to, and just looks nicer. Here the size we chose is probably a little large.

For the connector block you can add some heat shrink tubing at strategic locations to help keep things neat.

completed jumper cable
A little heat shrink tubing keeps wires together

Lather, rinse, repeat. We made a half-dozen three-pin jumpers that we can use for NeoPixels or servos and several four-pin connectors for I2C devices. The four-pin I2C connectors only have a connector on one end (power, ground, SDA, SCL) while the other end are normal breadboard pins: this lets us hook up I2C devices all neatly on the component side, and hook up the Arduino side where we need to: on the component, already breadboard-ready, the pins are right next to each other. On the Arduino side the pins are separate.

Product Links

We’ve used all of the products below. The Hakko tools come highly recommended. The connector sets are adequate (and cheap) but we prefer higher-quality pins. For the price they’re okay. The affiliate links come first, followed by direct links, and are labeled appropriately.

Affiliate Links

Direct Links

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