Question regarding micro powerup

Hello all,

I recently stumbled across this great forum. After a few weeks lurking and learning a lot I have my first post.

I'm waiting for some hardware to arrive before I can test something but I thought I would throw the question up to the Guru's on here for feedback.

For simplicity I will explain my (basic) circuit requirements.

I have a pic micro (TBC) and want this to be totally physically isolated from the battery when instructed by the micro. (it's a long story and is not for current consumption reasons.)

If I put a momentry push switch on the +supply line of the micro, what would the minimium time be that this would need to be pressed before the micro would power up, execute some code that would pull a pin high. This would fire a transistor to pull in a relay. A set of contacts on the relay would then be in parallel with the momentry switch, therefore when the momentry switch is released the relay contacts would still bypass the switch and keep the micro powered.

The code would execute and if necessary pull the relay drive pin low. The relay would drop out and all would be 'physically' isolated from the battery.

The only way to power up would be a momentry press switch actuation.

Please note. The battery has to be physically isolated so a relay is the only option.

I hope this makes sense

Thanks for any feedback.

If you write the microcontroller's code in such a way that the relay activating pin will be set "H" in the very begining, the "reaction" time will be basically the relay's contact closure delay - see picture below ..

Regards,
IanP

Ian,

Many thanks for taking the time to post the image.

I'm assuming at these timescales that a person simply pressing a momentry button will press it long enough for the micro to power up, output a line high, relay pull in and latch micro power.

Your image gives me a great starting point to monitor my circuit.

Cheers