Random outcome on multiple devices

[Aussie Barry]

Hi Art,

In what part of the "Land Down-Under" do you reside?
I am in Sydney's southern suburbs.

Thanks for the quick reply.
Noise detection systems are overkill for this project. I was hoping that the power up sequence for individual devices would have provided some degree of variation.
What if I used a timer based system to generate the seed and then de-tuned the internal oscillator between various devices to get some spread of variation - do you think that would work?
Alternately, I could cascade a pulse from PIC to PIC and emulate a button push... just thinking out aloud here.

Cheers
Barry
VK2XBP

[Art]

Close to Brisbane here

There are always things you can try. Maybe PicBASIC's POT command.
only instead of using a potentiometer, try a fixed value resistor,
and maybe a reading with POT will vary enough with temperature
(if you had to produce multiple units and keep firmware identical).

Once with the Sony PSP I got random numbers by looking at the audio input

[HenrikOlsson]

Hi,
It all depends on where you want to introduce the variation.... If you by "detune" the oscillator mean to tweak the OSCTUNE register slightly between devices then you might as well program in a different seed from the get-go - there will be a unique program in each device either way.

Perhaps you can use something like the RCTime command with an external RC (duh...) network to generate the seed and rely on the tolerance of the R and the C to get the needed variance.

/Henrik.

EDIT: Art beat me to it while I was typing and doing some other things.

[Aussie Barry]

Great suggestions guys - thank you.

I will look at the POT/RCTime commands and choose wide tolerance components or random values to achieve the desired variation.

Cheers
Barry
VK2XBP

[Art]

I can't help thinking there would be some noise on the power you'd see with ADC.
Interference between ADC pins has always been a problem...

[Aussie Barry]

I am not sure how I would go about un-tapping the noise to produce a random output.
Would you care to expand your idea for me?

Cheers
Barry
VK2XBP

[Art]

If the device is mains powered there's a 50/60Hz clock on the transformer secondary
the way old LED digital clocks used to keep time from mains signal.
If you are looking at that with a pic that has an independent clock the results will vary.

If you can run an ADC from internal RC clock

DEFINE ADC_CLOCK 3

and the pic from xtal, and look at any clock or output signal
generated by the pic program with ADC the results will differ as clocks lose sync.

I would try the resistor Cap network first (timing cap discharge via resistor).

[Demon]

(Never done this)

What about reading a resistor on analog pin? A high value, maybe 100K, would that produce a reasonably wide range of seeds?

Robert

Edit: since no 2 resistors are exactly alike, the voltage should vary.