Materials included
-Brass Rod 150mm long
-Red & Green LED
-Black and Red wire 2m long
-2 Resistors 1K Ω
-Red and Black alligator clips
100mm plastic tube 7mm Id
Shrink Tubing
-Black 2.4mm diameter, about 300mm long
-Red 6.4mm diameter, about 150mm long
-Black 12.7mm diameter, about 125mm long
Given these simple materials, a workbook and tools to construct our LED Logic probes.
following the wiring diagram we were provided with I started with soldering the Green LED positive leg to the first 1k resister, this is because the LED lights only have a voltage of 0.7v and with the battery having a voltage of around 12.6v that without the resistor the LED would of blown because the circuit would have a very high level of current or the maximum amount that the voltage source could of provided. After soldering the Green LED to the 1K resistor I had to solder the piece to the red wire, this is how the current travels through the circuit.To test that my connections are right I test the circuit by touching the red positive wire to the positive of the battery source and the negative side of the LED leg to the earth terminal, this completes the circuit for now and my Green LED lights up.
After finishing the Positive side of my Probe I start on the Negative side and Red LED light. I repeat the process as I did with the Green LED, with my Red LED connected to my resistor I connect that piece to my black wire and test the connection the same way I did with the green.
When I am happy that my connections are strong and stable and working well, I take my brass rod (which is a conductor, meaning that current will travel through it) I sharpen one end which will be the LED probe test end, at the same I tin the middle of the rod removing the outer layer of coating so that it is easier to solder the LED legs on later.
Once I have done this I take some of my black heat shrink and cover the exposed LED legs and resistor wires, this insulates the connection so that if that connection were to touch another exposed piece of wiring it would create a spark when attached to the power source. Each wired piece has to be individually insulated, but must leave the unattached LED legs outside of the insulating heat shrink because they must be soldered to that brass rod.
Before I can solder the unattached LED legs to the brass rod i have to insulate both ends of the rod, with more black heat shrink, this is so that the brass rod doesn't come into direct contact with exposed wires causing a short circuit.
before soldering the uninsulated legs of the LEDs to the brass rod I had to get some more heat shrink and pull it over the red and black wires and up onto the rod, positioning the two LEDs into the middle of the of the rod where is has been tinned and readied for soldering. Heating the heat shrink completes the wrapping around the wires and the rod, this will support the weight of the wires and prevent the insulated LED legs from breaking off. However when positioning the LEDs you must make sure that they do not touch the brass rod, otherwise this messes with the current flow and the LEDs wont work when supposed too. To attach the uninsulated legs to the rod the legs must be twisted around the rod, using your fingers or bottle nose pliers, then solder to the exposed tinned section of the rod. to give the LEDs extra support so that they don't snap off use a Hot Glue gun to glue just under the LEDs.
now the insulated piece must be covered in plastic tubing which gives the probe extra stability and strength, a piece must be cut out though to fit around the LED lights. this is almost the end of the construction of the LED light probe. the next few steps are just covering up the construction with a few more piece of heat shrink just to insulate the probe a bit more and make it look nice.
The end product should be a fully operational LED Positive/ Negative probe. Both lights should light up when connected to both the positive and negative terminals of a battery source, and only one LED should light up when connected to the battery source and touching either a negative or positive terminal with the brass rod.
following the wiring diagram we were provided with I started with soldering the Green LED positive leg to the first 1k resister, this is because the LED lights only have a voltage of 0.7v and with the battery having a voltage of around 12.6v that without the resistor the LED would of blown because the circuit would have a very high level of current or the maximum amount that the voltage source could of provided. After soldering the Green LED to the 1K resistor I had to solder the piece to the red wire, this is how the current travels through the circuit.To test that my connections are right I test the circuit by touching the red positive wire to the positive of the battery source and the negative side of the LED leg to the earth terminal, this completes the circuit for now and my Green LED lights up.
After finishing the Positive side of my Probe I start on the Negative side and Red LED light. I repeat the process as I did with the Green LED, with my Red LED connected to my resistor I connect that piece to my black wire and test the connection the same way I did with the green.
When I am happy that my connections are strong and stable and working well, I take my brass rod (which is a conductor, meaning that current will travel through it) I sharpen one end which will be the LED probe test end, at the same I tin the middle of the rod removing the outer layer of coating so that it is easier to solder the LED legs on later.
Once I have done this I take some of my black heat shrink and cover the exposed LED legs and resistor wires, this insulates the connection so that if that connection were to touch another exposed piece of wiring it would create a spark when attached to the power source. Each wired piece has to be individually insulated, but must leave the unattached LED legs outside of the insulating heat shrink because they must be soldered to that brass rod.
now the insulated piece must be covered in plastic tubing which gives the probe extra stability and strength, a piece must be cut out though to fit around the LED lights. this is almost the end of the construction of the LED light probe. the next few steps are just covering up the construction with a few more piece of heat shrink just to insulate the probe a bit more and make it look nice.
The end product should be a fully operational LED Positive/ Negative probe. Both lights should light up when connected to both the positive and negative terminals of a battery source, and only one LED should light up when connected to the battery source and touching either a negative or positive terminal with the brass rod.
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