Soldering End Connector Pins to Bare Wires    


A Useful Lesson Opens Many Doors

The end result of this tutorial. The end pin
has been crimped and soldered to the wire.
(Click to enlarge)
After working through this tutorial, you
can make end connector cables. These
allow you to easily plug the cable
onto the RAMB.
(Click to enlarge)
After working through this tutorial, you
will be able to make jumper wires.
The black heat shrink tubing is used
to insulate the connector.
(Click to enlarge)

With more and more companies providing off-the-shelf components, sensors, motors, and output devices, robotics is increasingly gaining favor with everyday folks. You no longer need a machine shop or a well equipped electronics lab to create sophisticated robots. Robotics has progressed almost to the point of true plug-and-play status. This tutorial is the first step toward making the wires and cables that will be used to plug these sensors and output devices directly to the RAMB or other microcontroller.

The steps that follow will teach you how to crimp and solder end connector pins to bare wires. This is one of those highly practical skills that can significantly increase your enjoyment and success in the field of robotics. For example, building your own sensors, soldering your own circuit boards, and repairing broken electronic components can help keep costs down and spirits up. After all, it feels great to learn new hands-on skills. (And if you are a teacher robotics, I'm sure you know that having enough connectors and jumper wires on hand always seems to be a problem, especially with a lab full of creative students who design increasingly elaborate robotic applications.)

Soldering end connector pins takes some practice and a lot of patience to do properly. (To do it improperly takes virtually no time!) It is not uncommon for beginning students to spend 10 minutes and many tries to properly solder one connector pin to the end of a wire, but after a while some will be able to do it in less than 60 seconds. So take your time and remember that patience is a virtue.

When you're done with this tutorial, you'll want to proceed to the next step and turn your soldered end pins into end connector cables or female jumper wires, which are shown in the images at the top of this page.

I'd sure like to hear from you.
If you find my tutorial helpful or if you would like to leave a comment, please send me an email.


Table of Contents for this Page

  1. Gather Your Materials
  2. Strip the Wires
  3. Attach the End Connector Pins to the Wires
  4. Crimp the End Connector Pins
  5. Solder the End Connector Pins
  6. What's Next


Gather Your Materials
Before we begin, gather the necessary tools and supplies.

  1. For this project, we'll need the usual soldering and crimping tools. These are pictured in Figure 1 and include a wire stripper, needle-nose pliers, pin crimper tool, solder, soldering iron, and soldering iron tip cleaner. (See my buying guide for more details about these tools.)

  2. Of course, the end connectors will be connected to wires. The wire can either be solid or stranded. In this tutorial, I will use solid 22 AWG (American Wire Gauge) wire but stranded wire will work just as well. In fact, I try to use stranded wire as often as possible since it won't break like solid wire does when it's bent a number of times. Sometimes, however, I need a rigid wire, and for that the solid wire does the trick.

    The length of the wire is unimportant, but they should be approximately the same length. Just for the record, the length of the wires I am using today is about 8cm.

    When making cables, you should use wires of different color as shown in Figure 2. Of course, the color of the wire does not affect its electrical properties, but you should follow normal coloring conventions.

     
    • See page 176 in my book for a description of the proper wiring coloring codes.

  3. End connector pins, shown in Figure 3. (Jameco P/N 100765.) These gold pins are suitable for wire whose guage is between 26 & 22 and can carry a current of 1A.

    Until you get comfortable crimping and soldering, you'll need a lot of these! Typically, my beginning students ruin about five connector pins for each one they do correctly. (So if they make two wires each with two end connectors, you'd better have on hand between 20 and 30 end connectors per student!) Each end connector costs approximately $0.10 to $0.14, so it can add up.

For a list of more tools, see my Equipment Buying Guide.

Click on the images below to enlarge them.


Figure 1. Some tools needed for the job.


Figure 2. Solid 22 AWG yellow and black wire.


Figure 3. End connector pins will be
crimped and soldered to bare wires.

[Return to the top.]


Strip the Wires

Now that the materials have been collected, it's time to prepare the wires to be crimped.
  1. Using the wire stripper (see Figure 4), remove about 4mm of insulation from the end of one of your wires. Be sure to insert the wire into the appropriate gauge slots.

    If you are unsure about which is the right gauge, try the larger slots (i.e., smaller gauge) first. Using a slot that is too small will do more than remove the plastic insulation -- it will also cut or nick the wire, weakening the wire and making it prone to breaking.

  2. The exposed wire should be about 4mm in length, as shown in Figure 5.

  3. Strip the ends of the remaining wires. (See Figure 6.)

Warning!
Only use the wire stripper (and all other tools) for their intended purpose! That is, the only job you should do with the wire strippers is strip wire. They are not meant to cut nails, paper, or plastic. (This message is targeted more at my students and less at the general population, although it is sage advice.)


Click on the images below to enlarge them.


Figure 4. The wire is inserted into the
appropriate slot of the wire stripper. Here,
I am stripping a 22-gauge (22AWG) wire.


Figure 5. About 4mm of plastic insulation
is removed from each wire.


Figure 6. The ends of the the remaining
wires are stripped.

[Return to the top.]


Attach the End Connector Pins to the Wires
Now that the materials have been collected and the wires stripped, it's time to prepare the wires to be crimped. When you're finished with this step, your wire will look something like the one in Figure 9 below.

Video!
If a picture is worth 1000 words, imagine the power of a video! In addition to the images and text below, I have put the remainder of this tutorial on video because I think it is helpful to watch someone actually performing these steps -- although I find that the still images show much more detail and my text is much more exacting than my spoken word. (Plus I hate the sound of my own voice.) The video is long (nearly 8 minutes in length), so I have formatted it for both broadband and dialup up access:

Solder Tutorial Broadband Download (7m50s, 27.8Mb, 320 x 240)
Solder Tutorial Dialup Download (7m50s, 2.34Mb, 160 x 120)


  1. Lay the stripped end of one of the wires into the channel of a connector pin. I find this easiest to do by holding the wire and end connector between the thumb and index finger of my left hand as shown in Figure 7.

    I've found that this is more difficult than it sounds. The idea here is to use one hand to hold the wire firmly in the connector pin channel. You'll need the other hand free.

    The connector pin has two sets of tabs with which to secure the wire. The thin, tall tabs at the end of the connector pin (shown by the blue arrow in Figure 7) are meant to grab the plastic insulation sleeve. The short, wide tabs in the middle of the connector (shown by the red arrow in Figure 7) will wrap around the bare wire. Eventually, it is under the short tab that we will apply the solder and it is here that the joint will be the strongest.

    Align the wire so the tall tabs on the end surround the very end of the wire's plastic insulation. The plastic insulation should not extend past these tabs. The correct placement of the wire is shown in Figure 7.

    The bare end of the wire should extend well into the channel created by the short tabs. However, it is important that the wire does not protrude far past these tabs. The correct placement of the wire is shown by the red arrow in Figure 7.

  2. Still holding the wire and end connector pin in the left hand, use the small needle nose pliers to gently squeeze both tabs together, as shown in Figure 8. You don't have to squeeze too hard; this step is simply a temporary measure that will make it easier to place the wire/connector pin combo into the crimper tool . In this step we are not trying to permanently secure the connector pin to the wire!

    After both sets of tabs have been squeezed shut, the connector pin should look like the one in Figure 9. At this point, you should be able to let go of the wire and the end connector should remain attached.

  3. Since the end connector pin is not yet securely attached to the wire, move on to the next section and securely crimp the connector pin to the signal wire. Once that is done, repeat the above steps for the remaining wires.
Click on the images below to enlarge them.


Figure 7. The stripped wire is placed into
the channel of the end connector pin. Be sure
that the insulation does not protrude past the
tall tabs on the end, and that the bare wire does
not protrude past the short tabs in the middle.


Figure 8. Gently squeeze both sets of tabs
together with the needle-nose pliers. This is
a temporary measure that keeps the wire and
connector pin together while it being placed
into the wire crimper.


Figure 9. After the tabs have been squeezed
shut, it will look like this. Be careful --
the connector pin is not yet securely attached.

[Return to the top.]


Crimp the End Connector Pins
We are now ready to crimp the end connector pins to the wires. Crimping does two things for us. One, it ensures the wire and connector pin will have good electrical contact; and two, it provides strain relief for the wire. Electrical conduction is ensured because the crimp tool will tightly wrap the short tabs around the bare wire. Strain relief is accomplished because the tool will wrap the tall tabs on the connector pin tightly around the plastic insulator. When you are finished with this step, your end connector will look something like that of Figures 14 and 15.

Here's how to crimp the end connector to a wire:

  1. Carefully position the tabs of the end connector pin into the small trough of the crimper tool, as shown in Figure 10. Note that the tall and short tabs point directly toward the small gauge opening.

  2. When the wire is correctly positioned inside the crimping tool, gently insert the end connector pin into the small gauge opening of the crimper and slowly close the jaws of the crimper, making sure that the tabs of the connector pin are fully surrounded by the walls of the crimper tool. Your crimper should look like the one shown in Figure 11.

    Be very careful that you do not dislodge the pin from the wire or that you do not pull the wire out of the pin. This seems like an easy step, but believe it or not, it takes some practice to get right. The first few times I used this tool was not pretty. Either my hands weren't steady enough and the wire was yanked out, or I didn't fully insert the tabs into the tool, or I put the connector pin in backwards. I find that holding the crimp tool in my right hand with the grooved side toward me works best.

  3. Once the jaws are closed around the connector pin, make sure that the tabs are fully enclosed by the crimper's jaws. The front and rear faces of your crimper should look like those in Figures 12 and 13. Notice that neither of the metal tabs extend past the edge of the jaws. Now squeeze the crimper like crazy to ensure that the tabs will wrap tightly around both the bare wire and the plastic insulation.

  4. Open the jaws (by releasing your grip) and remove the wire. It may be so tightly wedged into the jaws of the crimping tool that it will be difficult to remove. If this is the case, gently pry the wire and connector pin out of the jaws. If you are too forceful you could yank the wire out, break the wire, or bend the connector pin -- so be gentle.

  5. Inspect the wire. It should look like the wire shown in Figures 14 and 15. A properly crimped wire will exhibit the following properties:
    • The tall tab has a firm hold on plastic insulator (as indicated by the yellow arrow in Figure 14).
    • As indicated by the red arrows in Figures 14 and 15, the bare wire goes all the way through the "tunnel" created by the small tab, yet it does not protrude into the empty chamber. If the wire does extend into this empty channel, it may prevent the end connector from being able to plug into the header pins on the RAMB.
    • The space between the tall and short tabs is free of insulation, showing only bare wire (as indicated by the blue arrow in Figure 14). This is important because it is here that we'll apply the solder during the next section of the tutorial.

  6. Repeat these steps for any remaining wires you have.


It may be helpful to examine what poorly crimped end connector pins look like. You do not want your crimped connectors to look like these:

Examples of Bad Crimping

Figure 16. Click to enlarge.
This is bad because there is plastic insulation between the tabs. If we use this wire in the next step, we'll find that it will be difficult to solder the joint.

Figure 17. Click to enlarge.
This is bad because too much of the bare wire passes through the "tunnel" created by the short tabs. If we were to continue to use this wire, we would discover that we wouldn't be able to plug the connector onto any header pins or sensor leads.

Figure 18. Click to enlarge.
This is bad because there may not be enough of the wire within the small "tunnel" created by the short tabs. Since we can't see how much of the wire is within the "tunnel", we are taking our chances if we continue to use this wire. It is likely that this connection will be a weak one and will not provide good electrical contact.


Click on the images below to enlarge them.


Figure 10. Insert the tabs of the
connector pin so that they point directly into
the small groove of the crimping tool.


Figure 11. Insert the wire and connector pin
into the small groove of the crimping tool.


Figure 12. Make sure that both sets of tabs
are enclosed within the tool's jaws.


Figure 13. Once you are certain that the
connector pin and wire are properly situated,
slowly and firmly squeeze the jaws closed.


Figure 14. Note that the insulation is crimped
with the tall tabs (yellow arrow); the bare wire
does not protrude out of the small tabs (red
arrow); and bare wire is visible between both
sets of tabs (blue arrow).


Figure 15. The bare wire does not protrude
past the small inner crimp tabs.

[Return to the top.]


Solder the End Connector Pins
It's now time to solder the end connector pin to the wire. Some people will argue that soldering is not necessary, that crimping alone is sufficient. For the short term, they might be correct, but over time a connector that has been simply crimped will become loose and the electrical connection will be severely degraded.

You see, if the following steps are done correctly, hot solder will flow between the end connector and the bare wire. When the solder cools (which it will do very rapidly) it will permanently join the wire and end connector as one solid piece of metal. This makes the connection very strong and an excellent conductor.

Therefore, if you have the soldering equipment, take the few seconds required to properly solder your connectors.

When you are finished with the following steps, you'll have wires that are soldered as shown in Figure 25 below.

  1. Since soldering requires two hands (one to hold the iron and one to hold the solder) I find it helpful to use a "third hand" device (see Figure 19) to hold the wires steady while I apply solder.

    Covering the jaws of the alligator clamp with electrical tape (also shown in Figure 19) will protect the wire's plastic insulation from the clamp's sharp teeth, especially when the insulation softens due to the heat from the solder iron. One can also insert the metal end connector directly into the jaws of the "third hand" as shown in Figure 20.

  2. If your soldering iron has a variable temperature gauge (as shown in Figure 21), adjust the power so the iron does melt wire's plastic insulation before the solder flows into the connector pin.

  3. Before applying the soldering iron to the connector pin and wire, make sure that your solder tip is clean. (I find that the tip cleaner in Figure 22 does the job nicely.) To further improve the heat transfer, I like to put a tiny dab of solder onto my hot iron just before touching the iron to the component.

  4. You are now ready to apply solder to the connection between the wire and pin. Soldering is an art that requires patience and lots of practice. The idea is to use the soldering iron to simultaneously heat the bare wire and end connector. When both are sufficiently hot, the solder will flow evenly between the two pieces of metal. This is what you want; the solder should not clump or pool in one place as shown in the images at the bottom of this page.

    Touch the clean tip of the iron to the area between the two crimped tabs as shown in Figure 23. The iron should touch both the wire and the end connector pin at the same time. Keep your iron in firm contact with both pieces of metal, as shown in the figure. If the iron is not in constant contact, the metal will not get hot enough to melt the solder.

    After a second or two, both pieces of metal should be sufficiently hot and you can apply the solder to the joint described in the next step.

  5. With the iron still in place, gently push the solder into the joint between the wire and connector pin, as shown in Figure 24. The solder should flow evenly between the two pieces of metal, as shown in Figure 25. As soon as the solder begins to flow, immediately stop adding solder to the joint and remove the soldering iron from the joint. The solder will cease flowing and instantly harden. If too much solder is added to the joint, it will flow into the opposite end of the connector pin, clogging it, as shown in Figure 29 below.

    Allow the joint to cool for a few seconds before touching it.

    Warning!
    It is good practice to apply the soldering iron to your work for no more than about five seconds. If the iron is in contact longer than this, the prolonged heat may damage any attached components.


  6. Repeat the above steps for the remaining wire connectors.

  7. When you are finished with the soldering iron for the day, dip the tip of the hot iron into tip tinner as shown in Figure 26. This will prevent oxide build-ups, increasing tip life and causing better heat transfer.

    Also, do not forget to turn off the soldering iron when you are finished soldering for the day.


It may be helpful to examine what poorly soldered end connector pins look like. You do not want your solder joints to look like these:

Examples of Bad Soldering

Figure 27. Click to enlarge.
This is bad because the solder (indicated by the red arrow) is not making contact with the bare wire (indicated by the blue arrow). The solder is simply sitting on top of the connector and has flowed between the connector and the wire. In addition, there is too much solder.

Figure 28. Click to enlarge.
This is bad because too much solder has been applied to the joint. Additionally, the solder has not flowed into the channel between the wire and the connector pin. This is known as a cold solder joint and is one of the most common mistakes beginning students make.

Figure 29. Click to enlarge.
This is bad because too much solder has flowed into the channel as indicated by the arrow in the figure. This excess solder will prevent the connector from being fully seated on a header pin as shown in Figure 30 below.

Figure 30. Click to enlarge.
This is bad because the connector pin makes a loose connection with the RAMB's header pin. This is caused because too much solder flowed into the connector pin's open channel, as shown in Figure 29 above.


Video!
If you would like to see a video of the above tutorial, download one of the following movies. The video is long (nearly 8 minutes in length), so I have formatted it for both broadband and dialup up access:

Solder Tutorial Broadband Download (7m50s, 27.8Mb, 320 x 240)
Solder Tutorial Dialup Download (7m50s, 2.34Mb, 160 x 120)


Click on the images below to enlarge them.


Figure 19. A "third hand" clamping
device allows the use of both hands to
solder the end connector pin onto the wire.
A piece of electrical tape prevents the
sharp teeth from damaging the hot wire.


Figure 20. Another way to prevent
damaging the plastic insulation during
soldering is to hold the metal end connector
pin with the jaws of the "third hand".


Figure 21. Set the temperature on your
soldering iron so it won't melt the
plastic insulation.


Figure 22. Use a tip cleaner to remove any
oxidation from the iron's tip and thereby
improving the heat transfer from the iron to
the components.


Figure 23. Touch the clean tip of the solder
iron to the area between the two crimped tabs.
This will simultaneously heat the wire and
connector pin, allowing easy flow of the solder.


Figure 24. A small amount of solder is
applied to the hot joint.


Figure 25. The finished product. Notice
the solder has flowed evenly between
the metal wire and the connector pin.


Figure 26. When you are finished for the day,
clean the soldering iron tip with tip tinner.

[Return to the top.]


What's Next
So, now that we know how to solder end connector pins to bare wires, what can we do with them? In other words, what's next?
  1. With what we've learned from this tutorial, we can solder end connector pins to external LED assemblies, allowing us to plug them directly into the RAMB or other microcontroller motherboard. To learn how to make LED assemblies (shown in Figure 31), see my tutorial on making external LEDs.

  2. We can make end connector cables as shown in Figure 32, which can be used to connect sensors, motors, and output devices to the RAMB. To learn how to make these, see my tutorial on making end connectors.

  3. With a piece of heat shrink tubing, we can easily turn our soldered wires into insulated jumper wires as shown in Figure 33. These versatile connectors can also be used to connect sensors, motors, and output devices to the RAMB or other motherboard. To learn how to make these, see my tutorial on making jumper wires.

  4. With a couple of jumper wires we can connect a piezo buzzer (figure 34) or an audio transducer to the RAMB.

     
    • See Appendix G in my book to learn how to program the piezo buzzer and audio transducer.

Click on the images below to enlarge them.


Figure 31. We can solder end connectors
to an external LED.


Figure 32. We can now make
end connector cables.


Figure 33. Making jumper wires is trivial.


Figure 34. With a couple of jumper wires
we can connect a buzzer to the RAMB.

[Return to the top.]


I'd sure like to hear from you.
If you found my tutorial helpful or if you would like to leave a comment, please send me an email.


Copyright 2006, Chris D. Odom. All Rights Reserved