Momentary > 5 seconds > Latch

We can make up any-old-solution, but it'll probably be wrong for your needs, because we don't know what you need.

If this is a watchdog timer, for instance: you generate a pulse (the 'heartbeat') that indicates normal operation, and if it's absent for too long, flip a 'something happened' latch and light a trouble indicator. So, that can mean a clocked shift register, and at the end of the shift register, if that last bit ever goes high, it disables the clock input so it stays high. Every subsequent heartbeat resets the shift register, so only a five-seconds-without-heartbeat event is indicated. Or, alternately, every subsequent heartbeat resets the shift register UNLESS the last bit is high.

The important part of that, is that the latch indicates a pulse ABSENCE during five seconds, which isn't part of your description. The other important bit, is that the latched output might be cleared by a later pulse, or might not. Again, not part of the description.

Well it was a stupid post to begin with -- It's just for a "shutdown" LED -- power off gets it out of the latch.

I'll use an 8pin PIC and control the power LED -- make it steady for power on and then flash for "safe to power off".

Den tirsdag den 16. august 2016 kl. 21.35.32 UTC+2 skrev mkr5000:

why not use the gpio-poweroff driver that is what it is for

-Lasse

what are you talking about? please explain. the gpio pins lose any intelligence when the script ends -- which is way before actual shutdown.

it is not a script it is a kernel driver, it is what is used to turn off the power after shut down in systems that have hardware to support that

-Lasse

If I understood you correctly then how about something like this:

piglet

Well something like that came to my mind. But I was afraid of suggesting a 5 second RC into a schmitt trigger... High impedance and noise sensitivity.. or some such worry.

George H.

I know what you mean George, but I figured the OP's 5 second was not required with precision so I ran with an electrolytic (Al or Ta) timing cap as being near enough and would allow a timing R below 1Meg.

piglet

Oh right, A big Al 'lytic. When thinking about timing filtering I always think that a 10 uF film cap is the biggest I've got.

George H.