A counter of seconds with two integer values and two fractionary values using four SSDs (Seven Segment Display) and the Arduino's Timer2.
It also has a digital output to show as a PWM the period that moves forward the counter (this pulses have a duration of 10 ms).
Apart from that, it has a variety of comands that can be put in the serial terminal like "pause on" "pause off" "up" "down" or "period [number]" (the last one change the period of the counter)
The hardware montage is the same as described in the schematic below:
