Pre-lab 1: Introduction to Electricity

If you’re coming to this page from @arduinogirl, you can back up a step and read my first post introducing the site.

Electricity! There’s a lot to cover on that, especially where it comes from, which in the case of New Mexico is mostly coal fired power plants, and some (just a little bit) from wind farms on the eastern plains. But really, the electricity that comes out of the wall is coal powered, so lets acknowledge that right up front. There are more and more ways to power your arduino and your projects with solar cells, and ideally we’ll get there over the course of these labs. But starting with electricity- we’re moving electrons through a circuit from “+ ” to ” -“. That’s it. Any time we interrupt that flow, we are breaking the circuit. We do that intentionally when we add switches, and switches can take an infinite number of forms (that’s lab 1.2). Today we’re just going to move some electrons from a battery, through a resistor and an LED and back to the – side of the battery.

This is the 2nd most simple circuit you could make (you could take out the LED and still have a circuit, but you wouldn’t get any joy from it), and you probably did something like this in junior high. This circuit is kind of like taking the eggs from the refridgerator before you even begin to make cookies. Or maybe like writing “eggs” on a shopping list. We’re going a long way from this step, but I’m not taking anything for granted.

  • 1 9 v battery
  • 2 alligator clip connectors or 22 gauge connecting wire
  • 1 22ohm resistor (red-red-brown – get used to this, you’ll use these a lot)
  • 1 LED (that’s a light emitting diode, but you probably know that)
  • Eventually, you’ll want to have a multimeter, it’s important, but for now you can just trust in the circuit.

What the “schematic” looks like:

schematic with power, ground, LED & resistor symbols

What the real circuit looks like:

the simple circuit, with a 220 ohm resisteor between the LED & ground
the circuit using a breadboard, the way all prototyping will happen

Ways to blow this sh*& up: The LED has polarity, which means 1 end (usually the longer leg but not always esp with RGB LEDs) is +  and the other is -, reverse it in this case, not much happens, except you drain your battery faster.

Another way is to forget to use a resistor. You can have a nice little LED explosion. There’s just too much voltage coming straight through that little glass bulb. pee-kow! and gonzo. I’m haunted by the number of LEDs I have destroyed in this way.

Finally, there’s the closed circuit. All circuits need power (+) and ground (-). If your circuit misses that (and as things get complicated its easy to do) you can burn out a component, and have a nice little blow up with puffs of smoke and the smell of burning plastic. yum.

Ohm’s Law
Resistor color chart – there are a ton of these with a simple g-image search
resistor color chart app @ itunes (.99)

notes: I’m using a 9V battery here, but in class we use: rechargable 9V, USB power, wall power (more on that next lab) and rechargable lithium batteries. There are lots of ways to get power. Also, because I can’t cover everything that I will when I’m talking for 2 hours in a lab, feel free to use the comments to ask questions or post your own information.