The tachograph project

To understand and manage interrupts in our projects, I would like to offer you a very particular one, a tachograph, a device that is present in all our cars and whose mission is to account for revolutions, normally the engine revolutions, but also in brake systems such as an Anti-lock Brake System (ABS) and others.

Mechanical considerations

Well, calling it mechanical perhaps is too much, but let's consider how we are going to make our project account for revolutions.

For this example project, I have used a small DC motor driven through a small transistor and, like in lots of industrial applications, an encoded wheel is a perfect mechanism to read the number of revolutions. By simply attaching a small disc of cardboard perpendicularly to your motor shaft, it is very easy to achieve it.

By using our old friend, the optocoupler, we can sense something between its two parts, even with just a piece of cardboard with a small slot in just one side of its surface.

Here, you can...