When http://lhc.net.br was approached about having an electronics build night I immediately came up with a project: a led that blinked LHC in morse code. Having never built a circuit in my life I asked for the help of my fellow hackers and while some suggestions were made it become clear to me that the project was quite complex. So I re-targeted my ambitions and decided getting a led to blink would be a good start.
Step 1: Lighting a LED
Before we can blink a led we'll first turn one on(continuously). Do so we'll need:
- Prototyping board(strictly speaking not necessary for this step, but we should learn to use one for the next steps)
- A led of any color
- A battery
- Electrodroid app(obviously any other reference material would be OK, but this app is extremely easy to use and thus recommended)
First let's examine how a prototyping board(pb from now on) works. A pb is a collection of wires set in a specific way that makes it easy to build a circuit. A pb can be divided into 4 sections, 2 "power" sections and 2 "pin" sections. The power sections are on the sides and have blue and red lines on it. On the power sections every entry in a column(vertical) is connected. On the pin sections every row(horizontal) is connected.
Now that we now that, let's look at the electrodroid app, it's main screen offers numerous options, for now we'll use the "LED Resistor calculator" from the "Calculators" tab. Choosing it will display a diagram of the circuit to build. The diagram has three elements:
- The two parallel bars of different size denote a power source(in our case a battery);
- The line that moves up and down denotes a resistor;
- The triangle with a a line in its tip and two arrows denotes the LED.
For this example we're using a orange LED, so choose that from the drop down box in electrodroid, next tell it what's the voltage in your power source: 9v. With that information it will tell us how much resistance we need: 480 ohms, which as being lazy we can just approximate that to 500 ohms.
Now all that is left is to actually assemble the circuit. Connect one end of the LED to your resistor and the other end to the power source, the second end of the resistor will be connected to the second end of the power source. If your LED doesn't light up, invert its connection(LEDs need to have it's positive end connected to the positive end of the power source).
- I didn't have any 500 ohms resistors at hand and thus choose to use two 1000 ohms resistor in parallel(thus cutting effective resistance to 500 ohms).
- To know the resistance of a given resistor use the "Resistor color code" option in electrodroid's "Calculators" tab.
Step 2: Blinking LED
To have a led blink we need to have the power to it oscillate in the desired frequency. There are many ways to do this, in this instructable we'll use a NE555 circuit generously offered by http://jameco.com. Getting this circuit to do what we want will require use of two resistors and two capacitors.
Let's start by looking at the circuit diagram in electrodroid. From the "Calculators" tab choose the "NE555 Calculator" option. On it we input the frequency in which we want our led to blink, I choose 500 mHz, that is: blinking twice every second. This gives us the need for:
- Two 120 ohms resistor(which I approximated to 100 ohms, since I don't need precision in the blinking);
- One 10 micro Faraday capacitor;
- One capacitor of unspecified value(any one you have available will suffice).
This diagram is a bit different from the previous one, let's examine it. The three lines of decreasing size denote a "Ground" connection, all of which will be, for our purposes, the negative end of our power source. The "Vcc" marking indicates the positive end of the power source. The two parallel bars of equal size indicate a capacitor. Straight lines indicate connections with no components(wires). The numbers(1 through 8) in the diagram correspond to pins in the NE555 circuit.
In the actual "chip" to know which pin is which consider the following:
- The circuit will have a small circle in it denoting pin 1.
- Other pins on the same side will then be sequentially counted up to 4.
- On the other side, "facing" the 4 ping will be the 5 pin.
- Other pins on this side will be sequentially counted up to 8.
There is one bit of information which is not explicit in the diagram, that is our LED. The reason for this is because an NE555 is used to oscillate the current in the circuit and can be used for many things, not just blinking a LED. The points in which we'll connect our LED corespond to the "Vcc" and the "Output" markings in the diagram. Again if the LED doesn't turn on, try inverting it's poles.