In this article I explain how to make a logical tip easily and with easy-to-find components.
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Hello, such friends, today I bring you a very useful tool that we must always have in our workshop, nothing more and nothing less than the logical point of evidence. Although it is a tool that can be bought for little money, it is so simple that often it is worth doing it on our own and if we do it well, the result will not have anything to envy to those that exist in the market .
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Sound continuity tester
What is the logical tip
Well, for those who still do not know what a logical tip, because the explanation is quite simple. It is a tester that tells us by turning on a light when there is presence of positive voltage or negative voltage, and this is done by inserting the test tip into a cable or terminal that will be under test.
As seen in the previous figure, we have the diagram of a simple logic tip for 12VDC. This consists of power terminals (red and black alligators) that have to connect battery voltage, two resistors of current limitation that being interconnected give stabilization of polarity to the circuit of LEDs, the LEDs connected so that the positive leg of one is the negative of the other (one to indicate positive and one for the negative) and finally the sharp point with which the tests will be made.
Considerations for this simple logical tip
• The resistors must be the same, otherwise a LED will always light up, even if we have not connected the probe.
• The bridge between resistors is very important, otherwise we will put the LEDs in series and they will light both. It will turn off one or the other when we connect the probe ... it would be like a logical tip upside down.
• Always check the polarity of the diodes.
Proposed logical tip
Well, as you can see is a simple enough logical point, the only problem that I see is the need that needs a positive feed and another negative and good there are times when tests are done especially inside the vehicle find a positive It becomes a problem.
That is why I made this small redesign to our simple logical tip and it is as follows:
As you can see in the previous figure, it is quite similar to the previous one except that I included a 9V battery that feeds the circuit, a switch off and the combination of a resistance of 380 ohms with a led of high brightness of 1.8 mm white to place it on the tip so that it will shine in those places where there is little visibility.
As you will see, instead of two alligators for food; we will only have one, the black one. This to be connected to the chassis of the engine (negative battery voltage) will make common to the car batteries and the internal 9V so that our tool can work.
So with this logical tip practice we just have to have a negative that is very easy to get in the car, just connect it to a screw or any metal piece that is connected to the chassis and it will work wonders.
Considerations in this design
• The same as for the previous circuit. It is only important to add the suiche that turns off the logic tip, otherwise it will discharge the battery through the resistors and the high brightness LED.
You can see a video of how I made it
Well, it's all for today. I have no choice but to hope that you like this proposal and if you have any suggestions or questions because below is the table for it.
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