rotate bytes in array

[Acetronics2]

Hi, Art

a good question to ask : do you need to store the 30 values for another purpose than calculate your mean value ???

because @ each measurement you could calculate:

new_meanval = (old_meanval*29 + last_measure) /30 ... which gives you the mean value over the 30 lasts measurements ! ( called "rolling average", if I'm right )

note here 32 measures would be best for dividing time ! so :

new_meanval = (old_meanval*31 + last_measure) >> 5 ...

I think Darrel posted a while ago a nice routine about that ...

I remember he also posted about a 48 level stack ... may be ideas to take there ...

Alain

[Art]

Yes, the device is also a car alarm that is triggered by internal lights that come on when the vehicle door is opened.
The line is 12 Volts live until a door is opened & a resistor divider provides 5 Volts for the pic's input.
If ever I get a false alarm, I want to save the last thirty seconds voltage readings to see if I can prevent it.

When the car battery goes cactus my alarm might also sound since the resistor divider is at the unregulated side,
and may not produce the voltage for logic high at the pic pin.

I could have the program look at the last thirty seconds values to prevent these false triggers.

[amgen]

from your decription, the alarm part could be done with 1's and 0's, door opened/closed, no a/d overhead, just digital pin, "0" at < 2.5volts and "1" > about 2.5volts. No help checking batt voltage though...??
Don

[Demon]

Yes, the device is also a car alarm that is triggered by internal lights that come on when the vehicle door is opened.
...

Just a technicality; I'd feed directly from the door switch, not the lamp itself. You could have forgotten the interior lamp switch in the OFF position, the lamp could be burnt, or the robbers might know this trigger; they could just break the window, turn off the lamps and open the door.

I know it's highly unlikely, but it would make your device even better.

Robert

[Art]

It does get it's input from the door switch
It's live until any door is opened, then it is earthed.
That is why I might get a false trigger as the batteries die.