DAY 4:

Bread Board Logic Probe:

Today we make a very useful tool for electronics troubleshooting: The Logic Probe. The logic probe 'examines' the logic state at a particular point in an electronic circuit.' Basically, it can quickly gauge if the circuit connection is at high or low voltage. We use a 2N3904 transistor switch. It has 3 prongs--collector, base, emitter. Collector goes to positive, base goes to probe , and emitter to LED and common. It's fairly simple and cheap circuit to build.

Perf Board Logic Probe:

Once we have a breadboard model of the logic probe, we 'perfboard' the circuitry. It's quite straightforward, just the task of soldering can be challenging because there are so many ways of making and connecting logic probe circuitry. See below.

Transistors Switching:

The 2N3904 is a micro switch, a very popular transistor that can switch the flow of electricity, quite sensitive and versatile. It's a simple circuit that can incorporate the the finger tip as the push button. If you lick your finger and touch the circuit, the LED amplifies brightly as more current flows versus a dry finger tip. No touching with BOTH hand because it will create a complete circuit that utilizes your body to conduct the electricity. OUCH!!!

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.

DAY 2

Today was a busy day.

We got 3 handouts.

1. Using the multimeter

2. Introduction to using breadboard

3. Schematics, Ohm's Law and Potentiometers

Using the Multmeter:

Primarily we did mini exercises on continuity measurements, resistance measurements, and voltage measurements. On the continuity test, we used the ohm or resistance measurement of the multimeter. We used the circuit board we mad and check for breaks in the circuit. Since continuity in the circuit is non-directional, we can probe the board in any directions. We tuned the meter to a short-circuit beeper and so if there is continuity, it would beep. Resistor above a 100 ohm did not beep. Large capacitor beeps, small do not. OL also shows that the circuit is not connected.

Voltage Testing:

We learned of the science of AC/DC source. Alternating Current versus Direct

Current. I used the 5V power supply/transformer from yesterday as the main power source; the transformer steps down the 120V AC down to a 5V DC. To check voltages, we switch the mulitmeter's mode to DC Voltage. Using the probe, we test across 9V and 1.5V D batteries. Voltage is testable only when the circuit is powered on. In case of odd readings, use a "reference voltage" at hand to check if the meter working properly. Since voltage is directional, you can get positive or negative reading; regardless, always have the black probe on reference or ground. Lastly, we tested the wall wart. On a unregulated wall wart, the voltage measured is AT LEAST what's printed on the case. We used a 13.3 V unregulated rated at 12V which measure the voltage to be 11.1V with a 470 ohm resistor. However, a SWITCH MODE adaptor is lighter and smaller and are regulated. The one I made from yesterday was rated at 5.1 V and the meter reading was at 5.11V, incredibly accurate.

We also tested the wall output using the voltage meter. We measured it at 121.8V. In addition, we tested 5 resistor and learn to read the color of the resistors for it's value in resistance. A good mnemonic rhyme is Bad Beer Rots Our Young Gut But Vodka Goes Well, 0123456789, respectively. Lastly, we worked with a potentiometer and light sensor. The potentiometer acts like a logarithmic variable resistor and the light sensor increases in resistance with less lumens and decrease in resistances in more lumens.

Resistor Reading:

DAY 1

We went over the safety criteria for the class. We took a safety test that requires a 100% as passing. We went downstairs and practice soldering on a protoboard.

I completed the board with 40+ soldering points. You'll notice the good soldering is silvery and filled. The poor soldering is not as filled and not as silvery. I cut the ends of a 5.1V, 0.7 A cell phone power supply, split the wire and solder two leads to it, a black for ground and a red for power. Then I wrap heat shrinks onto the two leads soldered.

Pictures were taken of the protoboard and power supply unit for verification