Answers to Boncuk
Hi Boncuk.
Thanks for the quick response.
The vacuum switch is essentially an on/off switch that opens and closes a circuit. It does not provide a signal. Most of the time, it would be in the open circuit state. When the vacuum reached a user selectable point, the switch would close the circuit. On average, the switch would remain closed for perhaps three to five hours before the vacuum receded and the switch went back to the open circuit state. It would not matter if the 555 triggered again when the switch went from closed to open as the solenoid it operated would already be open anyway.
The need is to have the switch trigger a pulse of 10 - 15 milliseconds between 6 - 12 volts and a load of about 5 watts.
It would only operate on average perhaps once every two to five days so this would be a monostable circuit.
I don't want to confuse anyone so I have limited this discussion to only the opening of the solenoid. Once this part is figured out, the same circuit design would be applied to closing the solenoid. The process of closing the solenoid is essentially the same as opening it but the polarity on the pulse is reversed.
Regards,
jwcornell