How to make a lap counter

Many times, we want to know how many laps a wheel has done, or we simply want to keep track of activities, such as jumps, hits, etc. In this article, we will see how to make a lap counter which we can convert into a general counter, using the electronic addition principle of a calculator.

Materials

- An old calculator.

- A switch.

- Cables.

- Tin soldering iron.

- Silicone sealant

Arming our accountant

The first thing we are going to do is open the calculator, remove the circuit board from the case and locate the equals (=) key contact.

Once we have identified the two terminals of the equals (=) key on the circuit board, we mark them with a pair of toothpicks so as not to make a mistake when closing the circuit, as this would spoil our project.

Then, we turn the board over and position ourselves where the terminals are, identify the points to which we have placed the toothpicks and with the help of a tin soldering iron, we solder a pair of wires to the contacts of the equals (=) key.

Now, very carefully, we pull out the soldered terminal wires from somewhere on the calculator and close the case. To prevent the case from opening, we can use silicone as a glue.

Next, we connect the wires to a switch, this can be a simple electronic switch or a magnetic switch, it all depends on our imagination and what we want to tell.

This small device can be modified to become even a small kilometre marker for a bicycle or for counting steps while walking, or for any other activity we want to keep records of with a counter.

How it works

The way it works is simple, in calculators there is a little trick: when we press the 1, then the + key and then the equals key (=), an infinite counter is generated, similar to the one used in programming. Each time we type equal (=) one more unit will be added to our count and so on until we stop.

By removing the terminals and connecting them to a switch, we are closing the circuit in an external device that we can manipulate at will, to take advantage of this little trick of electronics and generate a digital counter of 8 digits in a very short time.