LED Test Light

   Howdy folks! We're back again with TTEC 4841-Easy Car Electrical. I'm Tommy Alpa Shepard aka Tung Nguyen will bring you an easy insight of a device which handles, without wasting over 30 bucks at an electrical store and probably would damage your circuit. Yes, it is the logic probe LED tester. Even though this is an individual practical assessment, before that, BIG THANKS to my classmate Umar for helping me familiarize with soldering- one of the central skills needed to successfully pull this off.
   ITS THE LOGIC PROBE and the logic is simple: All constructions are shown in this wiring diagram as a both general and detailed idea shaping: 

  Though all instructions were provided during this assessment but there are some points I'd like to emphasize. During construction using this diagram as an instructor, you need to be clear about 4 things:
1. Where to put components, orders .etc.
2. Where need soldering.
3. Where need insulated.
4. Last but not least, know how the electricity will flow in all situation.
  Order is very important. You might as well put the diodes LED the wrong way just because the long lead of Green which supposed to be soldered to the rod were hooked up with the resistor, and then you continued to follow everything else in perfect order. In the end you tested it and pissed off and wondered why the F*** it didn't work. Well, that's why. I guess you know what I mean.
  One thing I realize about this is knowing how the current flows is the second most important rule that saves your ass when things go whacky. Instruction says Green is for positive, Red is NEG. But if we take a closer look, we will definitely see why it is called LOGIC PROBE. Let say you make a mistake hook the long Red into the brass and its short soldered to the R2 resistor. Don't panic because you just make your Red a positive indicator, so why the hell cry while you can make the rest into a negative indicator. Whatever you do, no matter how big your mess is when start, just remember to check it before too late, and for your sakes please remember these are just diode LEDs, so make use of their nature.
   OK! Back to some educational interpretation. I'm going to explain how this works. As there are 3 remarkable terminal in the whole circuit: Red Alligator clip positive; Black Alligator Negative; and the brass rod is a free terminal or it can be referred to as a ground. There are also 3 main situations at which this Logic Probe will operate also 3 main ways that we have to test our probe:
1. Positive-Negative
This is when we connect the red alligator to positive of a 12V battery, and black alligator to battery negative. And the whole thing works just like a basic series circuit:

From positive - Resistor R1 - Green LED diode - through rod - Red LED diode - Resistor R2 - Negative
This means both LEDs will light up equally. There is no current flowing till any end of the rod because it is not grounded. If the rod is grounded when Pos-Neg is happening then we've got a short circuit.

2. Positive- Ground
Red Alligator to battery positive; rod touched with battery negative. The current will flow like this:

Electricity finds it easier to go through the end of the rod to ground, after doing its job brightening up the Green LED. This is why the Red LED doesn't go on, because flow doesn't even bother to go through the Red LED and then has to go though the very tough R2 1 k Ohm resistor in order to get to ground. Plus, the black alligator is on air.

3. Ground- Negative ( or Free Terminal- Negative)

 The rod is touched to battery positive, the black alligator is clipped with the battery negative. The current only flows through the Red LED to ground. The Red Alligator is on air, plus it is a diode, current can not flow back.

  So in the end, we know the theory, we know how to make it, we know how to test it, we know how it works. We are all the way up to using it in the future as a reliable tool for back probing- checking sensors, battery.etc..