DAY 3

Schematics,Ohm's Law, and Potentiometer:

Here we learn some basics of circuitry. First being able to read schematics, understanding the symbolism/electrical circuitry logic of the schematics are keys to trading information about circuits. The four basic symbols are resistors, power, ground, and LEDs. LED symbol depicts positive pin on left and negative pin on right. Often with simple wiring diagramming, we can reproduce simple to complex circuitry. Getting the schematics down would make the rest of this course much more enjoyable. Though some LEDs have build in resistors, typically a LED runs in series with a resistor, to create a voltage difference and drop in current. LED wouldn't light up unless there's a drop in voltage and too much current will burn it out. Since the circuit is powered by DC 5.1V, it's unlikely the LED will burn out, unless the resistance is below 100 ohms. Larger resistances will have a larger voltage drop and therefore dimmed the LED versus lower resistance on the same type LED, which will be brighter. A potentiometer was used as variable resistor to demonstrate that if you reduce the resistance, the current will increase, in which the LED will lit up brightly, but burn out. The forward Voltage and KVL helps to understand the behavior of voltage in a circuit. So in any loop circuit, the total voltage must be balanced, i.e. the amount generated = the amount used, known as KVL or Law of Voltages by Kirchoff. The forward voltage on the other hand is the "negative" voltage used by the LED. Here we use Ohm's Law, V=IR, to determine the voltage with give resistance and current. An unknown current can also be calculated give the resistance and voltage. By combining the concept of Ohm's Law and KVL, the brightness of the LED can be maximized using the 5.1V DC power supply and calculating for the resistance. The forward voltage of the LED taking into consideration here, which is usually about 2V.

Relays and Switches:

In this session, we learn how to turn our LEDs on and off using switches. We used a mini slide switch for breadboard and a slide switch. Then we develop a relay driven LEDs that uses low voltage or small current to 'switch' a larger voltage or hight current. It looks like relay has coils inside that increase the 'gain' of your switching energy. In the first relay driven LED, a push button will turn one light on and the other one off, vice versa; this relay was DPDT. Then we made a relay oscillator that switches on and off very quickly, so quickly that it sounds like a motor. A capacitor is added to slow the relay down and prevent it from burning out.