In the last lesson, you learned how to find signs of life from the MCU by blinking an onboard LED on the Wonder Gecko Starter Kit. I could spend some more time exploring all of the onboard circuits, and I will cover more of them in upcoming lessons, but the real fun starts when you can control off-board components with circuits that you build yourself. That’s the whole point of making things, right? In this lesson, you will build your own LED circuits on a solderless breadboard and control those LEDs with pushbuttons on the Starter Kit.
I am purposefully keeping the projects rather simple for these first few lessons while you get accustomed to the embedded world. This will make it easier to learn the basics before we ramp up the complexity in later lessons.
Materials Needed for This Lesson -- More info on the Maker's Guide Website
Working with Solderless Breadboards
One of the tricky things about creating your own hardware project is that you first have to find your components, figure out what they need to function and figure out how to connect all of those components to each other. It is not trivial, and there isn’t always a right or wrong answer. The difference between software projects and hardware projects is like the difference between multiple choice tests and “show your work” tests. It’s up to YOU to figure out how to wire those things together and keep things from melting.
Hypothetically, you could read about the requirements for the components that you have chosen, draw up schematics and design a Printed Circuit Board (PCB) to house your components, then wait a few weeks for those to be printed, assembled with components and delivered to you. What usually happens next is that you find out that you have inadvertently connected your most important part backwards and now you must wait a few more weeks before you can try out your circuit. While this arduous process is sometimes required for ultra-high-speed circuits, it isn’t usually necessary for most MCU-based projects.
There is a better way. You can connect those components to each other with the help of a solderless bread board. This has the benefit of giving you near-instant feedback about how your design works and lets you get working on the firmware while the PCBs are being manufactured.
Solderless Bread Board and Various Hookup Wire
The drawback to breadboarding your design is that you will end up with a tangled mess of wires, so use lots of colors and label and bundle your wires if it gets too hectic. Keep in mind as you breadboard that it is not going to be as reliable as a properly-built PCB with shorter traces between components. The objective at this stage is to ensure that you are connecting things together properly, but don’t expect a robust design.
Semiconductors have been shrinking in size constantly since their inception. It used to be that you could order a “breadboard friendly” version of a chip that you wanted to use in your design with big pins, but not anymore. In order to breadboard with the latest and greatest semiconductor technology, you will need to make use of breakout boards, which are boards that “break out” the very tiny pins (or in some cases balls) from Surface Mount Technology (SMT) components to a workable pin pitch – the distance between pins, usually 2.54mm or 0.1” – that will give you a way to connect them to your solderless breadboard.
Accelerometer Breakout Board with 2.54mm Pitch through Holes
Your Starter Kit is a partial breakout board. It breaks out some of the pins on the MCU to 2.54mm through holes along the edge of the board and also houses other circuitry necessary to get the part to function and connect to your computer through USB.
You can visit sites like SparkFun and Adafruit, as well as Mouser, Ebay and Amazon to find breakout boards or evaluation kits. However, they are not always available on the market and will cost more than bare chips.
Schmartboards 0.5mm SMT to 2.54mm Through-Hole Breakout Board
If you are brave and not afraid to learn new things, you can make your own breakout board. You can create them with bare breakout boards from Schmartboard for many component package types. You will need a fine-tipped soldering iron and perhaps a good magnifying glass or microscope to do the work. The solder is already on the board and the SMT devices fit into grooves to help you line things up so all you need to do is heat up the pins and traces. The benefit of this is that if you somehow destroy your component, you can just replace the component without paying for a whole new breakout board.
Build up an External LED Circuit
In order to use your Starter Kit with a bread board, you will need to solder 2.54mm through-hole header strips to the through-hole testpoints along the edge of your Starter Kit. You will find that soldering is something you will have to learn how to do sooner or later, at least on these 2.54mm pitch connectors. Soldering at this pin pitch is considered to be a beginner’s skill. Order some breakout boards and start practicing. Just attach the 2.54mm through-hole headers to the holes on the practice breakout boards for now. Then do the same to your Starter Kit. I like to solder my 2.54mm through-hole headers so that the plastic strip and longer leads are on the top side of the Starter Kit as shown in the picture below. For small breakout boards, I will solder the header strip to the bottom side of the board and plug them directly into the solderless bread board.
Be sure to use the header strips shown on the left and install the short leads in the holes in the board along the top edge of your Starter Kit, and then flip the board over to do all of the soldering on the back side.
TIP: The double-sided header strips shown on the right make good female-to-female adapters for your socketed breadboard wire.
When soldering the pins, try to keep the solder on one side of the pin and the soldering iron tip on the other side so that the solder “flows” between the two. You want to heat both pieces of metal that will be joined by the solder at the same time to ensure the best connection. See the diagram below. If you don’t get the round copper solder pad hot enough, the solder will ball up on the pin and it will not flow into the joint. This is known as a cold solder joint.
Soldering the Header Strips to the Starter Kit
Repeat this procedure for the bottom row of through-holes and the jumper location labeled J100. It is on the right side of your Starter Kit next to the pushbuttons. There are five holes aligned vertically on the board.
Now your Starter Kit should be ready to go with header pins on all testpoint locations.
In the next lesson, you will learn about the LED theory needed to connect to external LEDs.
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