Random ON/OFF Timer Circuit

That is correct, the cycle would continue to repeat.

Regards Tom

--
So, you want it to turn ON for a random interval of not shorter than 5
and not longer than 20 seconds, and then at the end of the ON period
you want it to turn OFF for a random interval of not shorter than 5
and not longer than 15 seconds, and then you want the cycle to repeat
forever?

--- Seems like you only need one. I'm working up a solution with an 8 bit PRSG feeding the broadside load of an 8 bit down-counter. When the counter times out it toggles a dflop wired as a divide-by-two (which turns the relay on and off), advances the PRSG by one state, and drives a 5 second one-shot which loads the counter with the new value from the PRSG and holds the counter off for 5 seconds.

In order to get the two timeouts, I'm using a 555 as an astable with the frequency switched from about 17Hz for the 20s timeout to about

26Hz for the 15s timeout. The dflop will switch the frequency by changing timing caps, since that's easier because they're ground referred.

Those numbers come from 256 counts in 15 seconds when the PRSG loads all ones into the counter for the 20 second timeout and 256 counts in

10 seconds when the PRSG loads all ones into the couner for the 15 second timeout.

I'll post the schematic to abse when I'm done. Hopefully, later on today.

-- John Fields Professional Circuit Designer

Pending a more elegant solution, you could adapt this circuit I designed for my 'Surf Synthesiser' many years ago:

That delivers an output duration (simulating gaps between successive breakers) chosen randomly from 10 preset values from roughly 9s to 20s (determined by the resistor choices). It sounds like you need TWO such

4017 sections, one for ON and one for OFF.

But if I was tackling your task from cold, I'd probably start by playing with a couple of pseudo-random generators made from shift registers.

--
Terry Pinnell
Hobbyist, West Sussex, UK

Neat! Look forward to seeing it.

--
Terry Pinnell
Hobbyist, West Sussex, UK

--- OK.

I've posted a schematic for you at alt.binaries.schematics.electronic under "Random ON/OFF Timer Circuit".

-- John Fields Professional Circuit Designer

Hi John,

Thanks for your help along with the other guy's replies too.

I have had a browse through alt.binaries.schematics.electronic under "Random ON/OFF....." but I haven't managed to see a link to the schematic.

Would it be appropriate to forward it to me direct at tmcmurtrie@@keystone.otago.ac.nz (remove the 2nd @)

Thanks Tom

Nice stuff! I'm hoping the OP will ask you for some narrative, as it would save me a lot of time .

But, hey, that's arguably even more complex than my 4017 suggestion!

--
Terry Pinnell
Hobbyist, West Sussex, UK

--
You\'re in luck!  He did, so I posted the circuit description and a
corrected schematic (sigh...) to abse.

Thanks. Looks good. Only wish I had time to either simulate or breadboard it .

--
Terry Pinnell
Hobbyist, West Sussex, UK