September 07, 2005

First Lab: Breadboard, LEDs and Soldering

To begin, I soldered the connections of the connector for the AC adapter. There is a diagram on the back of the AC adapter that shows a minus sign next to a line with a semicircle on it partially enclosing a small circle with a line to the right and a plus sign next to it.

Diagram of power connector.
This means the outer part of the connector is negative (ground) and the inner part is positive. So I soldered the red wire to the inside connector and the black wire to the connector's shell.

And a picture of the connected adapter:

I found that I had trouble getting the solder to melt until I learned to put the broadest part of the soldering iron to the metal that I could. Just using the point of it doesn't work well.

I also soldered two header pins onto the end of the connector so that it would be easy to plug the connector into the breadboard. I used a glue gun to put a daub of glue around the connectors to prevent the wires from accidentally crossing and shorting out:

Next, I needed to connect some LEDs. I first put one LED in series with a resistor and watched it light up. Then I tried two, and they both lit, but when I tried three there was too much voltage drop across them for any of them to light up. (The images are a little blurry because I had to turn off my camera's flash to catch the light of the lit LEDs.)


I decided it would be nice to have an indicator LED that I could just leave plugged in to my breadboard all the time to make sure it was getting power. I soldered a resistor to the positive end of the LED so that I would only need to plug in one component to test.

Next, I soldered leads onto a potentiometer. I soldered a red lead onto one of the outside connectors and a black end onto one of the other outside connectors, and a blue lead to the center connector. Todd explained to me that the potentiometer needs to have one connector powered and the other connector grounded in order for the center connector to be able to give a variable resistance. The outside connectors can be positive/negative or negative/positive, it doesn't matter. Switching their connection just switches which end of the dial is 0 ohms.

There was a push-button momentary switch included with my kit, so I decided to give it a try. I connected it with the LED-resistor combo I had made:

I found a two-position button on an old radioshack soldering iron in the "pre-loved items" bin, so I took it apart and pulled out the switch. I used the switch to make a circuit with three options: off, one led, and two leds.


You'll notice that there are two capacitors on the top end of the breadboard. The first is a 10 microFarad cap that goes between the raw incoming voltage from the AC adapter and the 5-volt regulator. The 1 microFarad cap goes across the positive and negative ends of the output voltage from the regulator. Todd explained that these smooth out the incoming and regulated voltages, and help prevent the breadboard equivalent of brownouts. As soon as I can find a single-position switch, I am going to use it to create an on-off switch that I'll connect between the regulator's output and the power strip of the breadboard. I'm also planning on leaving the LED-resistor permanently plugged in as a "pilot light" for my circuit.

Posted September 7, 2005 03:13 PM. Categories: Labs , Week 1 | Permalink