Thursday, February 18, 2010

Just who is this Ohm fella, anyway?

In some of my previous posts I've talked a bit about some electronics projects I've been playing with. I've had some very positive feedback so far, but I've also had quite a few questions. So before I go on I thought I'd explain some of the electronic terms I'm talking about and how they affect each other.

So let's start with current. Current is the volume of electrons flowing through a circuit. If you think of electrons as people walking through your haunt, then current would be the number of people that it would take to keep the haunt full.

Current is measured in amperes, commonly abbreviated as amps. Lets say your haunts pathway is wide enough to allow two people to walk side by side, and it's always full because your haunt rocks. So for the sake of this explanation we'll say your haunt draws two amps.

The width of the path in this example is what limits flow. That limiting factor is called resistance.

Hallways, doors, props, and actors all increase the resistance to the flow of people. Similarly, wires, resistors, caps, microcontrollers, and virtually everything else in an electrical circuit contribute to the overall resistance.

Since you've built such an incredibly awesome haunt you have people lined up for blocks waiting to get in. Those people don't like waiting in the cold so they start pushing on the people in front of them, causing pressure. That pressure is called voltage.

So now we have three basic elements of electrical circuit design: current, resistance, and voltage. Back in 1827 this German guy named Georg Ohm didn't have anything better to do, so he figured out how current, resistance, and voltage relate to each other. What he came up with was Ohm's law (Georg was a bit narcissistic). Ohm's law states that I = V/R, where I is current in amps, V is voltage, and R is resistance in Ohms. (Yes, resistance is measured in Ohms. I'll bet that stroked old Georg's ego.)

So lets say things are running smoothly in your haunt. Then unexpectedly a bus load of German tourists shows up to check things out. They've heard great things about the 3-axis flying crank trash can trauma you've built, and in their excitement they start pushing, increasing the pressure (voltage) on the people going through. In order to keep things running smoothly, you can either a: increase the capacity or speed of your haunt (increase the amperage), b: remove obstacles (decrease resistance), or c: sedate the Germans (lower the voltage).

As long as you know 2 of the 3 values, you can figure out the third.

This diagram will help with Ohm's law calculations. Cover the variable you're looking for, and then perform the remaining calculation.

(Note: I'd like to apologize to any German bus tourists - I meant no offense. I'd also like to apologize for any unintentional snarkyness in this blog post. I'm not sorry for the intentional snarkyness, though.)


  1. That is the best blog post title I have heard in a long time. Great information. And snarky fits me just fine! :)


  2. Is it even possible to sedate Germans? Good post - you gotta do impedance next.

  3. Three thumbs up... I borrowed 2 extra just for this occasion.

    I'll second Phil's suggestion. I hope it includes some various tombstones and a dash of snarkiness.

  4. Hmm, impedance. That's a complicated one. I'll get to it eventually, but I'd kind of like to stick to low voltage DC circuits at first 'cause that's what I'll be building for my haunt. Impedance doesn't really come into play in a DC circuit - it's a function of static resistance, frequency, and reactance.