You can now help support WorldwideDX when you shop on Amazon at no additional cost to you! Simply follow this Shop on Amazon link first and a portion of any purchase is sent to WorldwideDX to help with site costs.
Radioddity is giving away a radio for Father's Day! Click Here for details!
@linearone looks like a one-shot timer like the file name suggests.
With the switch open, both sides of the capacitor are pulled to the supply voltage. With the base high, the PNP transistor is off. When the switch is closed, one side of the capacitor goes to ground which temporarily pulls the other side down with it. When that happens, the base of the transistor is momentarily pulled down too, which turns on the transistor.
Two things turn off the transistor. With the switch held closed, the RC time constant will turn it off as the capacitor charges to 11.3v. It will also turn off (immediately, really fast) if the switch is opened since the left resistor pulls the - side of the cap to the + rail. With 12v already across the cap, this results in more than 12v at the base until the cap discharges back to its initial state.
Whatever this is for, it is triggering a short event the moment the switch is pressed and turns off shortly after.
This forum does not allow a single user to have more than one username. If anyone wants to change their username contact an admin and it will be done. Multiple accounts belonging to the same member will be deleted without warning.