Before explaining my great problem with my design, I will talk you about ABS Brakes.

An ABS system has, on each wheel a thoothed wheel and a magnetic proximity pickup. This generates pulses that are read in this case by the microcontroller. In order to the amount of pulses read in a time (for example in 1 second) on each wheel, the system will allow that wheel to brake or not. For example, if when braking the front left wheel speed decreases very fast, the system will interrupt the braking fluid in that wheel, so that it will not get blockaded. The braking fluid will act again when the wheel spins with enough speed.


I have developed a program that controls one wheel using the one external interrupt connected to one magnetic proximity pickup. The program is counting the number of interruptions in 200mS. When there are less than 10 interruptions in 200mS the microcontroller acts over a valve that interrupt the braking fluid. While the fluid is interrupted and if there are more than 10 int´s. the fluid is recovered and the wheel keeps braking.

And that works.

My big problem is that I have to control at least 4 wheels (the ABS system will be for a truck) and, of course, I don’t have 4 different external interrupts.

Does anybody know what can I do?

Thank you very much.