Hallo Manfred,

additionally to what Oleg stated, I want to focuse, that the signal to '/INT0' or '/INT1' must be very clean! Whenever your pig detetcor gives an 'active' signal, a very clean logical low state must be applied to '/INT0' input. No bounces are allowed!!! More, this logical low state must be maintained for at least 10msec, the time the oscillator needs to fully turn-on. After this period signal at '/INT0' pin must go high. Again, any bounces should be avoided.

So, what you need at '/INT0' and '/INT1' pins is a certain signal conditioning, which guarantees a stable logical low pulse of at least 10msec, consisting of clean edges at the beginning of pulse and at the end. Keep in mind, that servicing '/INT0', '/INT1' pins from power-down is totally different, than what is allowed during normal operation!

Another point to take into consideration is, that turn-on time of oscillator can last much longer than above 10msec, at certain conditions! This can be observed, when working at the temperature specification limits, for instance, or when using a poor crystal, showing increased equivalent series resistance. And finally, unsuited burden capacitances can also degrade turn-on time of oscillator.

So, it's wise to provide a some longer lasting low pulse to make the micro exit from power-down. In the following a simple monoflop (CD4538) can be seen to produce the logical low pulse:



Components are choosen for a pulse width of 100msec. The monoflop is connected in such a way, that a low to high transition at input 'A' will trigger the monoflop. As consequence, at its '/Q' output a low pulse of 100msec pulse width is emitted.
As input 'A' of monoflop shows Schmitt-trigger perfomance, even rather slowly changing signals from your pig sensor will safely trigger the mono.

Don't forget, that at input '/INT1' also such a hardware debouncing circuit is needed, if you want to exit power-down also from here (by the help of your 'place 1 to 8' switch)! Then, the CD4538 chips is very helpful, because it contains two identical monoflops.


Viel Glück,
Kai