# How to Build Solar-Powered Robots

This chapter is from the book

## Prototyping Circuits

To use solar cells, you need to level up your skills in laying out circuits. After a certain point, you need a way to connect and organize the wires and components. This section offers two ways; the first is using a solderless breadboard, which is a quick and easy way to prototype circuits. I’ll also show you how to solder, which uses conductive metal to stick components together. It’s fun!

As you can see in Figure 4.7, the breadboard consists of a grid of wire holes. What you can’t see is that conductors are hidden in the plastic, so some of the rows of holes are linked together and some aren’t. So, without ado, let’s examine a breadboard’s architecture:

• A.Ground bus—The ground bus is the strip of holes marked with a blue or black line. All the holes in this strip are linked together and typically are used for ground connections. Simply plug in the bus to your Arduino’s ground pin or the negative terminal of a battery pack.
• B. Power bus—The power bus is configured the same as the ground bus and marked with a red line on most breadboards. Plug your power supply here and then connect components as needed to power them.
• C. Terminal strips—These rows of holes are connected in groups of five, as marked in Figure 4.7. The various holes are given letters and numbers to help you organize your circuits.
• D. Notch—The notch in the center of the breadboard separates the two sides—none of the hidden conductors cross the notch. If you want to connect the two sides, you’ll need to use wires! When breadboard projects involve integrated circuits or microchips (ICs), the chip is usually positioned to straddle the notch, and this provides limited air cooling.

Here’s an example of a simple breadboard project. Look at Figure 4.8 and follow along:

• 1. Plug in a resistor from the power bus to one of the terminal strips. I used a 10,000-ohm resistor (known as a 10K, Sparkfun P/N COM-11508). It doesn’t matter which wire goes where.
• 2. Plug in an LED. I used one of Sparkfun’s violet LEDs (P/N COM-12704) and it ended up rather dim. You might try swapping in a lower value of resistor. LEDs are polarized, meaning that one lead is positive and one is negative, and if you put it in backward, the LED won’t light up. Put the long lead of the LED (positive) in the same terminal strip as the resistor. The short end (negative) plugs into the ground bus.
• 3. Attach a 9V battery to a battery clip (Jameco P/N 109154), with the red lead plugged into the power bus and the black lead plugged into the ground bus. The LED should light up!

### How to Solder

Breadboarding is well and good, but the best way to connect wires and components—assuming everything is working the way you expect—is to solder them. In this section, I’ll take you through a very quick but thorough guide to soldering.

#### Soldering Toolkit

You’ll need the following supplies to solder:

• Soldering iron—These come in many shapes and price points. You don’t have to spend a lot of money to get a quality iron, but the Radio Shack cheap one is not the solution. The two irons I use are a Weller WES51 (just Google that P/N to find one) and an Xytronic XY-258 iron (Adafruit P/N 180) that I keep in my toolbox.
• Solder—Solder comes in a great number of formulations and gauges. Here’s a great solder and I use it for all of my projects: 0.31—gauge, rosin-core, 60/40 lead solder. You can buy it anywhere (Adafruit has it, P/N 145).
• Sponge or tip cleaner—It’s important to keep your iron’s tip clear of residue, such as melted jumper insulation and baked-on flux. Some irons, like the aforementioned WES51, have a sponge that comes with it, but many soldering pros swear by tip cleaners like the Hakko 599B (Adafruit P/N 1172), which features a tangle of brass foil that cleans your iron without the need for a wet sponge.
• Vise—Small tabletop vises like the Panavise Jr. (Sparkfun P/N TOL-10410) help keep the printed circuit board (PCB) secure while you solder. Often they have suction cups or mounting holes for added security. You can usually hold the PCB in your hand or keep it on the table, so a vise is optional.
• Solder sucker—This is a tool for sucking up molten solder. Sparkfun has a cheap one
• Diagonal cutters—Use this for clipping off leads after you’re done soldering. Sparkfun has an inexpensive pair (P/N TOL-08794), and Adafruit has a nicer set made in Italy (P/N 152).
• Fume extractor—Soldering releases some toxic fumes. An ordinary desk fan or a specialized fan called a fume extractor (Jameco P/N 2171786) will keep those noxious gases away from your respiratory tissues.

#### Anatomy of a PCB

Electronic projects usually include a printed circuit board, or PCB. These typically consist of a sheet of laminate embedded with traces (wires) and solder pads, which are the tiny plates onto which the components are soldered. There are also instructions screen-printed on the material. Let’s take a closer look at the typical circuit board in Figure 4.9:

• A. Circuit board
• B. Screen-printed information
• D. Traces

#### Safety

Although soldering may seem dangerous—hot irons and lead poisoning!—I’m happy to say that it’s actually quite safe, as long as you follow some basic guidelines:

• Beware of what your soldering iron’s tip is touching. The tip is upwards of 600 degrees and can start fires and burn skin. However, tip burns are part of the soldering experience and can be treated as you would any burn.
• It’s suggested that you wear eye protection when clipping leads. These are the wires sticking out of electronic components, and they can go flying when clipped, potentially injuring you in the eyes. Better not to risk it.
• Solder is made out of lead, and that means that you shouldn’t ingest it. You should make a point to clean your hands and workspace after soldering. The latter can be cleaned up with ordinary household spray cleaner to make sure you’ve collected as much lead particulate as you can.
• The fumes are also toxic. You should solder in a well-ventilated room or use a fan or fume extractor to keep those fumes away from your face.

#### Let’s Solder!

If you have all the stuff you need, you’re ready to solder! I’m illustrating the process by assembling a Blinky Grid kit from Wayne & Layne (wayneandlayne.com or Adafruit P/N 549), so if you’re intrigued, you know where to find one.

Follow along with the simple steps outlined in the following sections:

STEP 1 Set Up the Work Area

You usually want your soldering iron close at hand, as well as a nice work surface. If you want accessories like a fume extractor or vise, now is the time to grab them (Figure 4.10).

STEP 2 Heat Up the Iron

Some irons don’t have an “on” switch; you just plug them in. If it’s got a switch, turn it on. Often an iron will have a temperature selector; if it does, set it to about 650 degrees, as you can see in Figure 4.11.

STEP 3 Tin the Tip

The first word in soldering iron maintenance is to “tin” the tip—basically, coating it in solder. This helps transmit heat, and if you tin your tip early and often, you will be rewarded with a hotter iron. Just touch the iron to a piece of solder and turn the iron around until the tip is coated, as you can see in Figure 4.12.

STEP 4 Insert the Component

This is fairly self-evident. Components have wires sticking out of them, called leads. The circuit board normally indicates if a component is polarized. This means the leads have to be inserted in a certain way on the PCB. Also on the circuit board are little metal disks pierced with holes. These are the solder pads. Slide the component’s leads through the holes in the solder pads, just like in Figure 4.13.

STEP 5 Bend Back the Leads

Turn the PCB around so you’re looking at the back. Bend the leads of the component (as you can see in Figure 4.14) so it won’t fall out when you solder.

STEP 6 Solder the Joint

Touch the iron’s tip to the lead and the solder pad for three seconds (Figure 4.15) and insert the end of a piece of solder. The solder should flow into the hole and rise into an even little hill.

STEP 7 Examine the Joint

Before you move on, take a gander at the connection. It should be a neat little hill, like in Figure 4.16.

STEP 8 Resolder as Necessary

Suppose your solder joint looks like the one in Figure 4.17—gooping up two solder pads. Grab your solder sucker, a spring-loaded piston that sucks away melted solder. Press down the plunger, then melt the solder with your iron while holding the solder sucker close. When the solder starts to flow, press the button on the piston and it will suck the solder away.

When the solder joint looks the way you like it, clip the lead as close to the joint as you can manage (see Figure 4.18). Ready for the next component!

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