Random ON/OFF Timer Circuit

Discussion in 'Electronic Basics' started by tom, Jun 1, 2005.

1. tomGuest

Hello All

I was wondering if anyone can help with or knows where I can find a
random ON/OFF timer circuit that will switch a 6-12v DC relay ON
between a random period of say 5 to 20secs and then turn OFF for
another random period of say 5 to 15secs.

I'm building an outdoor device and I'm trying to simulate random
movement.

Any help will be greatly appreciated.

Regards Tom McMurtrie

2. John FieldsGuest

---
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?

4. tomGuest

That is correct, the cycle would continue to repeat.

Regards Tom

5. Terry PinnellGuest

Pending a more elegant solution, you could adapt this circuit I
designed for my 'Surf Synthesiser' many years ago:
http://www.terrypin.dial.pipex.com/Images/Randomiser.gif

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.

6. John FieldsGuest

---
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.

7. Terry PinnellGuest

Neat! Look forward to seeing it.

9. Terry PinnellGuest

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

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

10. tomGuest

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
[email protected]@keystone.otago.ac.nz (remove the 2nd @)

Thanks Tom

12. Terry PinnellGuest

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