- Why do they call them computers?
- What do you use them for?
- What is hard about communication?
- What do computers add?
- Does it serve you?
- What is the difference between communication and expression?
- How can we encode more expression?
Summary of Topics Below
- Get Electrons to do your Bidding
- The Dreaded Short Circuit
- More About Electricity
- Breadboards –http://www.tigoe.net/pcomp/code/circuits/breadboards/
- LED’s , Buzzers
- Foam, Home Grown Switch http://itp.nyu.edu/physcomp/Labs/Switches
Get Electrons to Do Your Bidding
I have never seen electrons but believing in them is very useful. Basically they are simple creatures they want to get from one place to another. If you put some work in between, they will do it. They want to get from one side of the battery to other. From one connector on your computer to the other. (STAY AWAY FROM THE ELECTRICITY COMING DIRECTLY OUT OF THE WALL FOR NOW!) We are going use a wire as a road for them to make this journey. But the trick is we are going to place a light, a LED, in the way for them to light up on their way.
The Dreaded Short Circuit
These electrons are not completely benevolent. If you give them a free ride from one place to another they get too excited bouncing off the walls of the wire and bad things happen like your house will burn down or at leas your wire and battery might get very hot. Make them think they can get to the other side but make sure you use them up before they get to the other side. Add useless work for them (a resistor) if you have to.
Knowing more about Electrons
So far you are probably imagining electrons as horny little scrubbing bubbles (does anyone have such an image) desperate to get to the other side of the wire. People study this in a great deal more depth but the truth is you don’t have to go to much further before it is all pretty mysterious even to physicists. In digital electronics, the electricity is reduced to a yes or a no and we use software for more nuanced behavior. Without software your would need a much greater understanding of electricity to coax the electrons through more elaborate obstacle course of chutes and ladders called analog circuits. Even if for digital circuits you should know 4 things.
Things I Would be Ashamed If You Didn’t Know
- Positive is like an invisible cliff and ground is like the ground at the bottom of the cliff.
- Voltage is how High the cliff is. (Measured in Volts)
- Amperage is how many seat there on on the bus about to go off the cliff. (Measured in Amps)
- Resistance is how many shrubberies on the side of the cliff slowing the fall of the bus. (Measured in Ohms)
- Power is how bad the accident will be at bottom. (Measured in Watts)
Stuff You are Supposed to Know But You Probably Won’t Use In This Class
Most of the time we will be reading, not writing circuit diagrams so we don’t really need to know the theory behind them. Ohm’s Law (Resistance=Volts/Amps) is super famous but you may never need it. It does come in handy in making sure your circuit is not close to the dreaded short circuit. For instance if the LED is not enough work for those electrons they will make trouble. In that case you have to add a little “make work” in the form of a resistor to tire out the electrons. Most of the time there is a diagram (they call it a schematic) that tells you what kind of resistor to put in there.
Another formula Watts = Volts*Amps is useful for finding out how big a power supply to get. Occasionally you need to know how electricity behaves in parallel and in series. Using a multimeter might be important for debugging things like are you really getting 5V from the places you think you should be.
Rather than child-like pencil drawings, circuits are usually described in diagrams called schematics. To use them you have to learn the symbols.
The “AC” power coming out of the wall is big power that can actually move physical things or heat them up. Our task is really in the world of information where we are just need enough electricity to make a signal. In our world 5V or 3.3V is the signal for yes (aka 1,true,on, high, positive) and 0 Volts is a no (aka 0,false,off,low,negative). “AC” means alternating current which means that is switches direction many times every which would make a constant signal kind of complicated. So we are going to use “DC” or direct current. You can used a “wall wort” power supply to convert form AC to DC. Or you can get it directly out of a battery which is naturally “DC” power. Some people use voltage regulators. We know you are eventually going to be using a microcontroller (Arduino Brand) which can provide the perfect amount of power for your projects. It pulls the power from your laptop via USB and then has place for you to get +5V and Ground. You might consider detaching it from your computer while you fumble around with the wires on your breadboard and reattaching it once you think you have the wires settled.
Now you can say two things. Yes and No. I am home I am not home. I love you I don’t love you. A switch is two piece of metal that touch or don’t touch. The Electricity going through this circuit is not going to hurt you so you can . Your assignment is make a switch that is connected by something other than your fingers. Here is much more about switches.
Resistors resist the flow of electrical current. They reduce the voltage, and limit the current. The bands on a resistor indicate the resistor’s value. Here’s a handy resistor color code calculator. For our LED’s you can probably add a 220 ohm (Red Red Brown) or 570 ohm (Green Blue Brown) that will eat up the electricity not used by the LED.
Diodes are used as one way streets in circuits. In our circuit we are using a Light Emitting Diode (LED) which lights up when it performs it’s job. We don’t really care about the usual diode job of policing flow but really just the fact that it lights up. The key thing to know about a diode is that it is polarized, meaning that the two legs are not interchangeable. On most LED’s the longer lead (anode,triangle) goes closer to +5 and the shorter leg (cathode,line) goes closer to ground. LED’s may not eat up most of your 5V and risk looking like the dreaded short circuit without an added resistor. Less than a 1000 ohm, say 220 ohms should slow dow the electrons enough. If it does not light or is too dim, try without. If you don’t use any resistor the LED will probably just burn out faster but the superbrights may explode.
These allow you to connect wires without soldering. The holes in a row are invisibly connected underneath so just put wires in the same row to connect them. (rows are not connected across the center) will be connected. Why the long rows on the sides? Because our main trick is putting work for electrons to do in there journey from positive to negative those will be the most popular destinations on your breadboard and we dedicate the long row on the side for them. Only solid wire will work well with these holes if you like to use more flexible stranded wire for long runs to your sensors you have to put “headers” at the end that will fit in the holes. Here is much more about the breadboard.
To make good connections you have to use the soldering iron to heat the two things you are joining and then touch the solder to the joint not directly to the soldering iron. If you are impatient you will be tempted to just touch the solder directly to the soldering iron. You patience will be less tested if the tip of the soldering iron is clean and quickly conducting heat to the joint. You can clean the tip by melting a bunch of solder on it and wiping with the wet sponge. The really hard thing about soldering is that there are four things to hold (two pieces of the joint, the iron an the solder) and you only have two hands. You might use a clamp of some sort to help. Also don’t breath in the fumes. More pictures.
You need to create this circuit. You will notice that the connections in the breadboard do not visually resemble the flow of lines in the schematic which can make this simple circuit harder than it seems. Remember that the short end of the LED goes towards ground. Then ends of resistor are interchangeable and it can go anywhere in the circuit.
Now you need to replace the switch with something interesting. It can’t be a switch thrown by your fingers. Think about your butt, coffee cup, pedestrians, water, windows, cats, turns, newspapers, jumping, orientation, drawers, people who can only control their eyelash, crows, your butt (extra points for this), breath, balloons, infants, tongue, mosh pits etc… Check out the section in this about making your own switch.