Ode to Bodacious Breadboards, Part 3

I’ve said it before, and I’ll say it again, it’s a funny old world, and no mistake. When I first commenced writing Part 1 of this ever-growing mini-series, for example, I really expected to cover everything I wished to say in a single column. By the time I reached the end of that column, however, I knew there was going to be a Part 2.

It was only when I was in the middle of Part 2 that I realized we were destined to see Part 3, and—to be honest with you—at this stage in the proceedings I don’t see how we will escape a Part 4. On the bright side, I’m really enjoying this series. I only hope you are having as much fun as me.

Before we proceed, if you are a grizzled curmudgeonly old engineer who has served your time in the trenches, as it were, you may feel the following is too “lightweight” to warrant a spot on the illustrious Design News website. I beg to disagree for several reasons. Let’s start with the fact that Design News is home to a wide range of community members, many of whom are just starting out in their careers. Also, it scares me how many electronic engineers come out of college without having ever wielded a soldering iron in anger. These are the folks who will really benefit from the simple tips and tricks shown here.

At the end of my previous column, I presented you with a poser. This started with my showing a picture of a portion of a breadboard circuit featuring two groups of eight 150-Ω resistors including their full-length leads plugged directly into the breadboard. I’ve included a slightly different view of these resistors in the image below.

Two groups of eight resistors. CLIVE "MAX" MAXFIELD

Next, I posed two questions. First, I asked if you could envisage any potential problems that might arise from doing things this way? The answer to this is easy-peasy lemon squeezy. It’s not uncommon for someone to brush against one of the flying leads or for something else to occur that causes two or more of the resistor’s leads to touch. This can lead to some very interesting (often intermittent) errors that are a pain in the nether regions to debug.

Second, I asked if you could think of a cheap-and-cheerful solution that would make things neater and less prone to failure while also offering the opportunity to speed up future prototyping projects. The answer to this is the topic of this column.

One solution is to purchase pre-packaged resistors presented in dual in-line (DIL) packages. For example, consider the Bourns 4100R Series devices. If you look at the 4100R Series Data Sheet, you will see that these are available with different numbers of resistors in a variety of configurations (isolated resistors, bussed resistors, and dual resistors).

The ones we are interested in here would be eight isolated resistors in a 16-pin DIL package. These certainly provide the neatest solution for what we are doing, but they aren’t the cheapest option when it comes to prototyping. Also, they offer only a relatively limited number of resistance value options. As fate would have it, whatever value I’m hoping for is typically not one of those that are available.

But turn that frown upside down into a smile because there’s another option. In previous columns, I’ve mentioned my friend, Joe Farr, who hails from a small village outside of London. Joe is a whizz with respect to both hardware and software. He’s built an electronics workshop in his back yard that has me drooling with envy.

One reason I love chatting with Joe is that I always learn something from him. For example, when I showed him the picture of the breadboard with all the resistors, he said that if he’s ever doing anything more than one time, he typically solders those components onto a small breakout board (BOB).

Joe suggested that this is what I should do with my resistors, so that’s what I did. The two main options start by taking a piece of stripboard or prototyping board. I opted for the latter in this case, thereby saving myself from having to cut any tracks using a utility knife or a special stripboard track cutting tool.

We have two main options at this point. We can either use a fine-toothed hacksaw to cut the board between the rows and columns of holes (see [a] in the image below) or we can use a utility knife to score the board along the appropriate columns and rows and then snap it along the score marks (see [b] in the image below).

Sizing the board. CLIVE "MAX" MAXFIELD

I opted for the later approach in this case. Whichever technique you use, it doesn’t hurt to run a file over the edges to smooth things out a tad.

The next thing we’re going to need is some 0.1 in. pitch header pins that are long-tailed on both sides. These stick out 6.25 mm on both sides with a 2.5-mm piece of plastic in the middle, making them 15-mm long in total.

The image below shows two 8-pin strips of these header pins, two individual pins, our cut-down piece of prototype board, eight 150-Ω resistors, and a small breadboard. You want to use an old breadboard for this sort of thing because flecks of solder and fragments of wire can get stuck in the holes. These can cause all sorts of problems if you subsequently try to use the breadboard to implement a working circuit, so you should mark the board “NOT FOR USE!” (I just did this to my own board while I was thinking about it.)

Preparing the parts. CLIVE "MAX" MAXFIELD

What are the two individual header pins for? I’m glad you asked. I used these pins to create a little jig to bend my resistor leads as shown in the image below. The way I’m bending my pins, it’s a lot easier to do so on this 2-pin jig than it would be on the 16-pin rig with which the other pins tend to get in your way.

Preparing the parts. CLIVE "MAX" MAXFIELD

Once we’ve gathered all the parts, the next step is to plug the two 8-pin strips either side of the breadboard’s centerline as shown above. Also, insert the two single pins toward the other side of the board, along with a bit of “spacer board” (which I forgot to show).

Jig to bend resistor leads. CLIVE "MAX" MAXFIELD

Observe that I also employed a thin strip of prototyping board under the resistor on the 2-pin jig to keep the header pins separated. Actually, the way in which you bend your wires is another decision you will have to make. As you can see in the image above, my personal choice is to go for full loop.

We will return to this consideration in a moment, but first we must make a small digression because this next point is VERY IMPORTANT. You may be tempted to solder both the breakout board and the resistors to the header pins at the same time. DO NOT DO THIS! It’s extremely important to solder the breakout board first as illustrated in the image below.

Solder the breakout board first. CLIVE "MAX" MAXFIELD

While soldering the breakout board, you want to use a reasonably hot soldering iron and let the solder wick (get sucked through) the via all the way to the other side. If you try to solder the resistor at the same time, you may find the solder doesn’t penetrate all the way through the board. In this case, when you plug the board into your project breadboard, you may find the header pins separate from the breakout board (sad face).

While I think of this, if you haven’t soldered before, but if you feel you’d like to dip your toes into the soldering waters, then may I make so bold as to suggest a great book called The Basic Soldering Guide Handbook that was written my good friend Alan Winstanley.

OK, now let’s return to the topic of bending the resistor wires. Once we’ve soldered the header pins (see [a] in the image below), one option is to simply bend the resistor leads at 45°, solder the resistors to the header pins, and snip off any excess lead (see [b] in the image below).

Which way do you bend? CLIVE "MAX" MAXFIELD

An alternative is to twist the leads through a full 360° circle, solder the resistors to the header pins, and snip off any excess lead (see [c] in the image above). In either case, I would solder the resistors from the bottom (that’s “bottom” in the context of these diagrams) because—based on the way I hold my soldering iron—this keeps existing joints out of the way of new ones.

Which of these techniques is best? That depends on what you mean by “best.” Joe favors the 45° bend technique because he always thinks in terms of reworking things, which is a common occurrence when you are prototyping. The 45° bend makes it simpler to prepare and solder, and easier to remove if required later.

By comparison, I tend to favor the full 360° circle approach because my mindset tends toward mission-critical and safety-critical applications in which “failure is not an option,” as they say. On the downside, this approach takes longer to prepare, it increases the chance of forming unwanted solder bridges with adjacent pins because the joint is bigger, and it’s less amenable to being reworked. On the other hand, this is one solder joint that isn’t going to fail easily.

As Joe sagely says: “To each is own.” It’s hard to argue with logic like that. My finished eight x 150-Ω resistor breakout board is shown below (I’m sorry about the fuzzy photo).

Eight x 150-Ω resistor breakout board. CLIVE "MAX" MAXFIELD

In addition to being cheap-and-cheerful, the advantages of this approach include the fact that you can use the exact component values you wish, and you can mix-and-match values if you desire. You aren’t going to have problems with resistor leads touching each other, and you can quickly swap one breakout board for another if the need arises. In my case, for example, I might decide to switch to a 7-segment display whose LEDs have a different forward voltage drop, thereby requiring me to modify the values of my current-limiting resistors. Speaking of which, the image below shows my spiffy new breakout board (upper right-hand corner) in the context of the clock project I’m currently creating.

CLIVE "MAX" MAXFIELD

Well, that’s all for now. Until next time, I welcome your insightful comments, penetrating questions, and sagacious suggestions. Also, if you have any breadboarding tips and tricks you’d care to share, please feel free to email me at [email protected].