Random Timer

[ASuperJohn]

Hello all, I am very new to the site and was wondering if I could get some help on a project that I am working on. I will describe below what I need and would be happy to hear ideas on how to implement.
1. Should be as small as possible
2. Should be able to work off rechargeable battery or 120v ac
3. Needs to generate an output for random period of time from 5 sec to 20 sec or so
4. Needs to generate the above output randomly from between 12 hr and 24 hr or so
5. Needs to have no operator interaction at all
6. Can use any method to achieve the above
7. Needs to be able to drive a pizo speaker as the output
8. Once the output is active and reset the random timer for 4 sets a new time
I have been looking into using a PIC but as yet have not been able to determine if it alone could handle the demands of the requirements.
Thanks for any help or advise that you may have. John

 

[MikeMl]

I would use this technique. CMOS shift register and low power clock oscillator.

 

[ASuperJohn]

Thanks for the reply Mike, but I did some research on the shift register and can not quite figure out how that and the low power clock oscillator solve all the problems that I am having. How do I use this to create the random time for the output then the random time for the output to fire? I read on several of the sites about there needing to be a seed number and that there is a way to generate random numbers with the shift register, but I am not sure that I can hold the number and then compare that number to the clock to set the output. Any more details would be really great. Thanks
John

 

[KMoffett]

Since the times are all variable, an extremely accurate clock is not necessary, so it looks like an 8-pin µController would do it all. Although there a ton of options out there, I will recommend a PICAXE. Cheap ICs (~3.50USD), free BASIC programing/simulator software, a serial (or USB-to-serial) programming cable, and a very supportive user forum.

Ken