A fully analog circuit that activates an open-drain transistor for 1.5s after having waited 3s for the power supply to stabilize.
The timings can be adjusted by changing the RC circuits component values.
It is currently designed for a 12V power supply and can drive any power switch from 1.8V onwards.
The circuit will rearm itself only when the board 12V is removed then reapplied. Thus, it is possible to do a software reboot of the PC or powering it off like with a normal power button.
Digital timing diagram :
Steps :
- Before the timing diagram event labeled
1, the power supply is not present and the button output is kind of floating. - The +12V power supply is applied at the event labeled
1. The button output stays high due to a pull-up connected to the +12V. - After about 3.5s, the button is pressed (its output is forced to ground). This is the diagram event labeled
2. - The button is kept pressed for about 1.75s, then it is released. This corresponds to the diagram event labeled
3. - After that, the button is never pressed again until the whole power supply is removed then reapplied.
Bare PCB :
Assembled PCB :
Prototype :
The prototype has been made with recycled parts from old broken machines.
