Logic Probe Parts List:
Red LED:Black 2.4mm diameter,about 300mm long
Green LED:Red 6.4mm diameter,about 175mm long
Black wire 2 meters long:Black 12.7mm diameter,about 125mm long
Red wire 2 meter long
2 resistors 1KΩ
Red alligator clip
Black alligator clip
100mm plastic tube 7mm ld
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Wiring Diagram:
The wiring diagram looks like this:
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Soldering the parts:
The LED's, 1KΩ resistors,and wires are then soldered together to look like the picture blow.
Insulation of resistors:
Using the small heat shrink insulate both resistors and LED legs,(from the black and red wires to as close as possible to the LED) see picture below.
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Brass rod:
Using the correct safety equipment and grind a point on one end of the brass rod then insulated with heat shrink for 60mm starting 10mm from the point, leave a 10mm gap and fit a 75mm heat shrink of the same diameter so it insulates the blunt end of the rod as shown in the picture belows.
Tin the gap between the two pieces of brass rod; this will make it easier to solder the LED legs on later.
Before soldering the uninsulated legs of LED's to the brass rod, cut two 15mm pieces of the blue heat shrink and slide them both over the red and black wries and up onto the rod, get the LED's into approximately the correct position then heat the heat shrink. This will support the weight of the wires and prevent the insulated legs of the LED's breaking off.
Position the LED's to sit just above the rod, making sure that the insulation protects the insulated legs of the LED's from the brass rod. Twist the uninsulated legs of the LED's individually around the brass rod and solder to the tined section as shown in the picture above.
Before continuing, use the Hot Glue gun and glue under the LED's to give them extra support.
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Fitting the plastic support tube:Select the 100mm length of 10mm diameter plastic tube and cut a groove out of one end. This groove needs to be as long as the two LED's are in line, pluse 5mm that when fitted will extend past the LED's as shown in the pictures below
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Improving the appearance:
To improve the appearance cut the 20mm length of the 10mm black Heat Shrink. Slide it on from the pointed end of the brass rod. It may be necessary to squeeze the plastic tube together so the heat shrink will side right up close to the green LED. Now carefully heat the Heat Shrink evenly all the way around until it won't get any smaller.(It won't pull down tightly on the brass rod at this point).
Next cut a 90mm length of the 10mm black Heat Shrink and slide over the wires up onto the other end of the plastic tubing and heat shrink as above.(Refer picture below).
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Twisting and securing wires:
Twist the wires neatly and fit 15mm lengths of the red heat shrink every 500mm along the wires. Don't twist last 300mm of the wire as Alligator clips need to be attached to the ends of the wires.(Refer picture below)
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Fitting Alligator clips:
Remove the plastic covers from both the clips and install the correct way around on the appropriate coloured wires. Strip the insulation and twist about 10mm of each wire tightly. Insert the twisted end of the wire through the claws provided. Cut off the excess twisted wire and solder joints.
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Refitting Alligator clip covers:
To refit an Alligator clip cover it is helpful if you squeeze the clip wide open and make the jaws grip onto a screw drive, then slide the cover into place and release the screw driver from the jaws. Repeat on the other Alligator clip.
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Testing:
This tester is only for 24 volts or less, DC volts only. Connect the red clip to battery positive and the black clip to battery earth(negative). Both red and green LEDs will light. This tests the connections and that the tester is properly connected. Now touch the brass probe end to the positive battery terminal and the green LED goes out, and the red LED gets brighter. Touch the probe to the earth battery terminal and the red LED goes out, and the green LED gets brighter.
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Questions:
1.Why do both the red LED and the green LED go when you connect to the battery?
When I connect to the battery the current come through the red LED to green LED to the end of negative, so both the red LED and the green LED go.
2. Why does the green LED go out when the probe contacts the battery positive?
When the probe contacts the battery positive, the current come through the brass rod, but can't go through the green LED, because the green LED is one way to pass the current, so the green LED goes out.
3.Why does the red LED get brighter when the probe contacts the battery positive?
When the probe contacts the battery positive, the current come through the brass rod to the red LED to the negative, so the red LED get brighter.
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