A dial tachograph

For a more complete example in this section, we will build a tachograph, a device that will present the current revolutions per minute of the motor in a visual manner by using a dial.

The motor speed will be commanded serially from our computer by reusing some of the codes in our previous projects.

It is not going to be very complicated if we include some way to inform about an excessive number of revolutions and even cut the engine in an extreme case to protect it, is it?

The complete schematic of such a big circuit is shown in the following image. Don't get scared about the number of components as we have already seen them all in action before:

The tachograph circuit

As you may see, we will use a total of five pins of our Arduino board to sense and command such a set of peripherals:

• Pin 2: This is the interrupt 0 pin and thus it will be used to connect the output of the optocoupler.

• Pin 3: It will be used to deal with the servo to move the dial.

• Pin 4: We will use this pin...