Hackster Classroom for Teachers and Parents: Making Connections – Part I

One of the more challenging aspects of learning to create electronics projects is figuring out how to connect up disparate parts. What are some of these weird-looking connectors even called? How are we supposed to know what to use? In a classroom setting, there are more constraints, too. Typically a school can’t afford “make and take” products, so any connections need to come apart again cleanly and reconnect many times without breaking.

Back in our first Hackster Classroom article Getting Started with Electronics we introduced various microcontrollers and when it makes sense to use each one. Some of these boards have many sensors and other features already embedded. Sometimes, though, there is a capability a project needs that requires more than these onboard sensors, and this means that we need to connect up multiple electronic parts. We can’t cover the whole universe of possible connectors, but we can make a start.

There is no fundamental difference between connecting a microcontroller like a micro:bit to an extra sensor and connecting up the components that make up a laptop or desktop computer. Many of the more permanent connection schemes, therefore, are used commonly in consumer electronics. Since these connectors are not marketed quite so much to consumers (with exceptions like USB cables) a little background vocabulary is necessary before we can go shopping.

There is a whole thicket of acronyms and standards. There are two major parts to the subject of making connectors: the physical connectors themselves, and the standards and software that let the hardware they connect talk to each other. We focus here on connecting one thing to one other thing at a time. Connecting many things to each other is an option too, and that requires some sort of bus which is more than we want to wade into here.

In this article, we introduce some common physical connectors that we might find useful in classroom projects like the robotics projects we talked about in our Getting Started with Robotics Part I article. In our next piece, we will focus more on the standards and software. Most of the components we will be connecting up run on 3.3 or 5 volts, a sphere commonly called “low voltage."

The most typical thing we want to do if we are adding something to a microcontroller will be to add a component that needs to be supplied with power, a connection to ground, and some ability to send and/or receive signals. What kind of signals those are, and how to find out how many wires we need connected where, we will also get to in Part 2 of this article.

Alligator clips

As an absolute beginner, we might use a board with large holes for connections, like an Adafruit Circuit Playground Express or a BBC micro:bit. (Historically these holes were for sewing the board into wearable tech projects using conductive thread, and we can still do that, of course.) To add another component that is not already on the board, most people will start off using alligator clips. As the name implies, these clips have jaws on the end that can clip into the hole. These are reasonably sturdy, but the clips can be tough to use for small (or arthritic) hands. They have the virtue that they can be taken on and off easily so that project parts can be used by students in class after class.

Sometimes the plastic sleeve slides off, and the best way to get it back on is to clip them onto a pencil with the sleeve all the way off, then slide the clip back on.

Alligator clips will tend to slide around, and it is easy (particularly on a micro:bit) to short out connections if two alligator clips happen to touch. Thus they are not great if the processor is going to move around a lot, as with a wearable project. Alligator clips might have these clips on both ends of a wire, or they might end in another of the connectors described below.

Banana plugs

Banana plugs are similar to alligator clips, but instead of having jaws that clamp around the edge of a hole, they have springy sides that hold them inside a hole of the appropriate diameter. This lessens the risk of two of the connectors touching. Like alligator clips, multiple banana plugs may be needed depending on the device.

A big advantage of the banana clip over the alligator clip is that the banana clip is stackable. That is, the connectors are designed so that we can have several connected to one hole on a board. This is useful if we want to connect power and ground to several things, for example. The holes in a micro:bit (as well as a Circuit Playground and a few similar boards) happen to be just the right diameter to use with banana plugs. Unfortunately, unlike true banana plug receptacles, it's easy to push the plug in too far and end up with a loose connection. This is easy to work around by putting a plastic spacer in between. Cheap 4 mm inner-diameter nylon spacers (5-6 mm in length) work well for this, or we can 3D print a spacer that will cover all the holes at once.

However, just because we can make a connection does not mean we should. Piling up multiple connectors in a micro:bit hole may attempt to draw too much current through the micro:bit, damaging it.

Header pins

In this article, we are focusing on connecting up a circuit without soldering. No-solder projects will tend to be more expensive than soldering up a project from smaller pieces, but will be more reversible. If students have soldered together their pieces, it will most likely be a one-time enterprise. This means that we need to buy parts with header pins already attached, or otherwise have connections holes or pads. These are metal pins typically spaced 0.1" (2.54 mm) apart. There are also female headers, which male header pins can plug into for board-to-board connections, but only if we have the right pins in the right order (more on this in part 2). This is how daughterboards like an Arduino shield or a Raspberry Pi HAT (Hardware Attached on Top) or crust are attached to the main board.

There are also connectors for wires designed to interface with header pins. The most common ones used in DIY electronics projects are called Dupont connectors. Sets of jumper wires with individual Dupont connectors (either male, female, or one of each on opposite ends) are ubiquitous. There are also wires with a Dupont connector on one end and something else (like a banana plug or an alligator clip) on the other.

Extension boards

What happens if we need to have more connections than the basic board will allow? There are many extender boards for micro:bit that allow a user to get at many more pins in addition to those corresponding to the big holes. The CRICKIT board from Adafruit adds pins to a Circuit Playground Express and various similar boards. There is also a CRICKIT version for the micro:bit.

Power

Connection might not be enough, however. Some components (notably motors) are power-hungry and will need separate, additional power, whether from a second battery or other connector. Motors will need a motor driver (or controller), which can in turn manage power. This board’s physical connections, expected protocols and software will need to be compatible with both the particular microcontroller and motor, as we will discuss in Part 2 of this article. One exception is a small hobby servo. These have their own motor controllers built-in, but have limited capability.

Breadboards

A breadboard is a common way to connect more than one or two external components. This is a board that has rows of holes, some of which are electrically connected to each other. Most breadboards have two columns with rows of five pins each.

These rows of five pins are electrically connected so that jumper wires or other components (like header pins, LEDs, resistors, etc.) plugged into them make connections with each other. Between these two columns is a central gap suitable for spanning with DIP (Dual-Inline Package) devices like chips, switches, and even some breakout boards.

There are also typically rows running the opposite direction along the edges of the board (sometimes called bus strips) intended for supplying power (VCC) and ground (GND) connections to any rows that need them. (The breadboard shown has these bus strips labeled “+” and “-”, but the intention is to use them for VCC and GND respectively.)

Many microcontroller boards have a pair of rows of header pins the right distance apart (typically pointing down) so that they can be plugged directly into a breadboard. Devices with a single row of header pins can also often be plugged into one directly. For other configurations, or for making connections between components connected to different parts of the breadboard, we need jumper wires.

Jumper wires

There are many different varieties of jumper wire. Some look like giant staples and so can be a bit tidier when there are a lot of connectors. These are typically color-coded by length, which has the downside that color codes then may no longer imply the wire’s function, such as the standard of using black wires for ground and red for power connections.

Male Dupont connectors are often used as breadboard connections, with the female end connecting to component header pins. There are also female header pins that are appropriate for making board-to-board connections with male header pins (only if we have all the right pins, in the right order!), or for plugging in male Dupont connectors.

Solid-core wire can plug directly into a breadboard. If the diameter (or "gauge") of the wire is appropriate, strip the insulation from the end and insert it into the hole. This is, in fact, how the "giant staple" jumper wires are made. Solid-core wire has a single, solid piece of metal making up the wire, unlike stranded wire, which has many thinner strands inside the insulation. These strands allow the wire to bend more easily, avoiding wire fatigue which can cause the wire to break inside its insulation as a result of repeated bending.

Only use solid core wire in applications where it will be bent into shape to make a connection once, and will not undergo subsequent flexing in use. This also means that solid core wire should not be reused in multiple projects. One exception is the "giant staples" that can be pulled out and put back into the breadboard without changing their shape, as long as they are not bent to try to span a shorter distance.

Screw terminals

Another way to connect a wire to a breakout board is through screw terminals. Instead of a connector going in a hole, insulation is stripped from the end of a wire and then the wire inserted under a screw. Screwing down the wire makes a good connection. These are often included for wires that might need to carry more power than a header pin is recommended for, especially for connecting to devices like motors that are likely to come with unterminated wires attached.

When inserting stranded wire into screw terminals, it is important to make sure that the strands are all twisted together, and that there are no loose strands that may short to an adjacent terminal. A better strategy is to use solid-core wire when appropriate, or to crimp a ferrule onto the wire to create a more solid connection.

People comfortable with soldering may be tempted to "tin" the wire by putting a little solder on the exposed strands to keep them together before inserting them into the screw terminal, but this is not recommended.

Competitive robotics

We will not explore larger robots here, like the ones we talked about in our Competition Robotics article. These have a plethora of connectors, some specified in competition rules. They also need heftier wire that depends on how it is being used and an understanding of a wider variety of safety procedures. As a side note, the LEGO small robotics universe has its own connector standards (not necessarily interoperable among its families of kits). LEGO EV3, for example, uses RJ-12 connectors. These are like an RJ-11, but with the clip offset to one side. The newer LEGO Spike Prime uses a proprietary LEGO plug, the LPF2.

Examples

For some examples of connecting servos and LEDs to a micro:bit, check out lesson plans we wrote to create an “electronic familiar” (where we are using “familiar” in the sense of a wizard’s assistant). They are linked to our Nonscriptum website projects page. Scroll down to Lesson Plans and select Designing Role Play Props with Micro:bit. Here on Hackster.io, try searching for micro:bit or Arduino projects, and see how the author has connected the pieces.

Bottom line

In this article we reviewed a few common types of connectors and when we might use them. This is by no means exhaustive, and only applicable to the types of low-voltage hobbyist projects that we can build with a micro:bit, Arduino, Circuit Playground, or similar processor. However, the hardware connections are only part of the story. These connections need to be supported by software and standards that govern what kind of signals are sent over them. We will get into those next time in Part II. Talk to us on the Hackster Discord channel (use this invite if not in the group already) in the #-educator-parent topic and let us know your questions!