How to make a logical tip

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In this article I explain how to make a logical tip easily and with easy-to-find components.

How to make a logical tip

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 .

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.


punta logica simple

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:

como hacer una punta lógica

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.

punta logica

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.

Ahhhh can give your impressions of this article by writing your opinion up on the opinions button.

Written by 
Dennis Garcia



Muy buena tu propuesta.


punta logica

muy muy bueno amplio criterio y buen conocimiento de las corrientes en maya sos electronica. bueno suerte y nuevamente grasias



Sigue adelante con tus proyectos! me encantan!


Muy buen trabajo

Agradecido por la información

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How to make a logical tip

How to make a logical tip

In this article I explain how to make a logical tip easily and with easy-to-find components.

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11 Question(s) answered

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  • Asked by Gonzalo Hernandez
    on 06/27/2017
    la pila solo puede ser de 9v o se puede poner una pila doble aa Answer:
    No es posible...lo menos que podrias poner 3 pilas AAA para que te den 4,5v suficientes para que encienda el led.
  • Asked by Gonzalo Hernandez
    on 07/22/2017
    gracias Answer:
    A la odern! jejeje.
  • Asked by Taller cansino
    on 07/25/2017
    Ola chica...mecánica...tengo un pequeño problemita...con un carro 2.0 jeta...mi pregunta es cuántas alimentación es de voltaje debe un jeta mod 95 A3..2.0...muy buenísimos tus videos se aprende bien ...gracias...bendiciones... Answer:
    Hola que tal, bueno el Jeta no no cocozco porque no llego por aca, pero con respecto a la alimentación ¿a que te refieres? ¿la de la punta lógica?
  • Asked by julio
    on 09/25/2017
    hola,se pueden unir los led y resistencia con cable. grcias muy amable saludos Answer:
    Hola Julio, claro con cable lo puedes hacer mientras hagas bien la conexión.
  • Asked by manuel salvador castro
    on 10/27/2017
    como hacer un probador de imyectores automotriz Answer:
    Hola manuel, en este artículo te muestro como Es simple y sin muchos componentes.
  • Asked by eduan
    on 11/10/2017
    para una punta logica de 24 voltios se utilizan los mismos componentes gracias por todo Answer:
    Hola que tal Eduan, debes duplicar el valor de las resistencias y listo! lo puedes usar sin problemas a 24V.
  • Asked by jean perez
    on 12/27/2017
    buenas noches es posible que lo haga sin el led de alto brillo y sin la bat de9v solo lo quiero para identificar pocitivos y negatvos Answer:
    Hola Jean, sin la batería de 9V seria una punta logica corriente, tendrias que agregar muchos metros de cable para hacerla. Y quitarle el led es simple, solo no conectas el led y la resistencia asociada. Pero si me diste una idea para redactar un articulo para hacer una punta logica corriente. jejejeje. Saludos...
  • Asked by Javier ap
    on 12/29/2017
    Ola saludos gracias por la informacion me a servido gustaría saver q escaner me puedes recomendar....bueno un economico....gracias ...por tu apoyo Answer:
    Hola Javier, ¿pero de que pais eres? para poder darte una buena respuesta.
  • Asked by jesus miranda
    on 03/06/2018
    hola buenas tardes la punta lógica que tiene la batería de 9v no puede trabajar con 12v Answer:
    Claro jesus, puedes usar una pila de 12V de las de control remoto de carro sin problemas. O si la pregunta es que si puedes conectar esta punta a 12V del carro, la respuesta es si.
  • Asked by Lopez
    on 03/17/2018
    Buenas noches buen trabajo kisiera saber si puedes hacer probador de continuidad con sonido graciasy muy buenos videos Answer:
    Caramba...seria muy buen proyecto. Voy a trabajar en eso amigo Lopez.
  • Asked by luis ospino
    on 05/15/2018
    como hacer una punta logica digital, con tecnologia TTL y CMOS Answer:
    Que tal Luis, esas hay bastantes en Internet. Incluso vi una que le colocaron un display y muestra 1, 0 Muy popular. jajajaja.

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