Ode to Bodacious Breadboards, Part 4

Everyone has their own prototype powering preferences.

6 Min Read
Clive "Max" Maxfield

At a Glance

  • Wiring a breadboard the right way conveys confidence to continue.
  • This includes jumpers to mitigate split rails, connections at opposite ends of the board, & two LEDs.
  • Many beginners find it difficult to wrap their brains around the concept of a diode’s forward voltage drop. Read my analogy.

I was just skimming through Part 1Part 2, and Part 3 of this ever-expanding mega-mini-series when I realized we had not yet covered the topic of how to power our breadboards.

Of course, this depends on what we are trying to achieve. As we discussed in Part 2, some people, like my friend Joe Farr in the UK, create designs featuring analog circuits requiring 0 V (ground), +12 V, and –12 V, coupled with digital circuits requiring both +5 V and +3.3 V. Some of these circuits require the analog ground to be separated from the digital ground.

Many times, even purely digital circuits require a mix of supplies, such as +3.3 V for the microcontroller and +5 V for some of the sensors, for example. In this case, a breadboard with split power and ground rails can be very efficacious. On the other hand, as we noted in Part 1, some split-rail breadboards fail to reflect this fact by means of the red and blue lines that indicate the rails (that is, they don’t show gaps in the middle). I’ve spent more time than I should trying to debug a non-existent problem with my circuit, only to discover that the real issue was that one half of my breadboard wasn’t being powered. “Oh dear,”* I said when I tracked down the underlying problem (*or words to that effect).

Related:Ode to Bodacious Breadboards, Part 1

All engineers have stories like this. For example, Joe once told me he spent one head-scratching session trying to debug a breadboard prototype that wasn’t receiving power at all. He thought he was powering it from one of his bench power supplies. He kept on returning to verify that the supply’s main (red) light-emitting diode (LED) was on; also, that the supply’s Channel 1 (green) LED was on. It was unfortunate that his breadboard was, in fact, connected to Channel 2.

In my case, I spend a lot of time building little hobby projects based on the Arduino Uno R3, which supports 5 V digital inputs/outputs (I/Os). Via its header pins, the Arduino also provides +5 V and 0 V (GND) that can be used to power the breadboard via flying leads.

Assuming we don’t want to do any soldering, then one way to power a breadboard is as shown below. Observe the horizontal links in the middle of the power and ground rails at the top and bottom of the board. I always add these just in case this is one of those sneaky split-rail boards that’s trying to trick me again (“Catch me once; shame on you. Catch me twice; shame on me,” as the old saying goes).

max-0064-01-breadboard-power-v1.png

When I start working, I always orientate my breadboards such that the red (power) rail is at the top and the blue (ground) rail is at the bottom. Being consistent like this helps cut down on inadvertent errors.

Related:Ode to Bodacious Breadboards, Part 2

This is probably a good time to say: “Pick a wiring color scheme and stick to it.” In my case, I use red wires for +5 V and black wires for 0 V. Once again, being consistent helps cut down on inadvertent errors.

I bring the power (red) and ground (black) wires from the Arduino into the bottom right-hand side of the board. I add two wires on the left-hand side of the board to connect the lower and upper power and ground rails. And then I add two LEDs along with their current-limiting resistors on the right-hand side of the board.

I’m using green and blue LEDs in this case because … why not? Now, before I do anything else, I power-up my Arduino and ensure these two LEDs light up my life with their cheery glow. This tells me that all my power and ground rails are alive and well and waiting for action. (I also use a multimeter to verify that I’m seeing +5 V ±0.1 V between the power and ground rails in the top right-hand corner of the board because I don’t want to discover later that I have a bad board with a high-resistance rail somewhere. 

As an aside, these green and blue LEDs both typically have a forward voltage drop (VF) of 3 V and a maximum forward current (IF) of 20 mA (always check the data sheets associated with any components with which you are working). Using Ohm’s law, V = I × R, so R = V / I, so R = (5 V – 3 V)/0.02 A, which means our minimum current-limiting resistance value would be 100 Ω (with brown-black-brown) colored bands. But a LED’s brightness is a function of the current, and this would be annoyingly bright. I’m showing 680 Ω (blue-gray-brown) resistors in the above diagram. This will limit the current to ~3m A, which will be much easier on the eyes.

Related:Ode to Bodacious Breadboards, Part 3

As another aside, beginners can find it difficult to wrap their brains around the concept of a diode’s forward voltage drop. What does this actually mean? Well, in words, it means that if the diode is presented with any voltage less than this value, it simply won’t conduct. Once the supply voltage exceeds the forward voltage drop, it will start conducting like a champion (although a real-world diode will have a small internal resistance, we usually assume this value to be 0 Ω as a first-pass approximation).

This is true of any diode. The only (well, main) difference between a regular diode and a LED is that the latter emits light when it’s conducting. The best analogy I’ve seen for this is illustrated below.

max-0064-02-led-forward-voltage-drop-analogy.png

Assume we have a lake, which we are using to represent a power source like a battery (or the Arduino, in our case). Now assume that there is a brick-lined channel at one side of the lake. This channel represents a conducting wire. The height of the water in the lake is equivalent to voltage in volts. Any water flowing through the channel is equivalent to current (in more ways than one).

In the case of (a), if we assume that there’s 3 feet of water in the lake and that the bottom of the channel is level with the bottom of the lake, then all 3 feet of water is free to flow through the channel.

Now suppose we build a wall and raise the floor of the channel by 3 feet as shown in (b). This wall is equivalent to the forward voltage drop of our diode. Since the wall is the same as the depth of water in the lake, no water will flow through the channel.

Finally, in (c), we keep the base of our channel 3 feet higher than the bottom of the lake, but we increase the depth of the water in the lake to 5 feet. As a result, we now have 2 feet of water flowing through our channel.

I know that analogies are always suspect, but I must admit I’m rather proud of this one. I wish someone had presented things to me this way when I was starting out. If I ever get my time machine working…

OK, that’s all for now. As always, 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].

About the Author(s)

Clive 'Max' Maxfield

Clive "Max" Maxfield is a freelance technical consultant and writer. Max received his BSc in Control Engineering in 1980 from Sheffield Hallam University, England and began his career as a designer of central processing units (CPUs) for mainframe computers. Over the years, Max has designed everything from silicon chips to circuit boards and from brainwave amplifiers to Steampunk Prognostication Engines (don't ask). He has also been at the forefront of Electronic Design Automation (EDA) for more than 35 years.

Well-known throughout the embedded, electronics, semiconductor, and EDA industries, Max has presented papers at numerous technical conferences around the world, including North and South America, Europe, India, China, Korea, and Taiwan. He has given keynote presentations at the PCB West conference in the USA and the FPGA Forum in Norway. He's also been invited to give guest lectures at several universities in the US and at Oslo University in Norway. In 2001, Max "shared the stage" at a conference in Hawaii with former Speaker of the House, "Newt" Gingrich.

Max is the author and/or co-author of a number of books, including Designus Maximus Unleashed (banned in Alabama), Bebop to the Boolean Boogie (An Unconventional Guide to Electronics), EDA: Where Electronics Begins, FPGAs: Instant Access, and How Computers Do Math.

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