how do I stop 555

[djTopcat]

Im trying to build a 555 circuit for my grandson, next electronics hobbyist.
I have a photo resistor to turn on a 555 by way of pin 4 reset. The 555 load drives a simple rooster sound circuit. The whole thing works fine when a light hits the photo. My question is, How do I stop this thing. ??? Once the photo resistor sees light and starts the rooster, it cant cycle and shut off. A few seconds is fine but a few hours is a bit much. Anyone know how to shut the 555 off after a certain time.

 

[zachtheterrible]

thats probably going to take more than a simple 555 circuit. your input (the photoresistor) is going to stay on in the sun obviously, so you'll need something to let it send a signal just once, and then that signal needs to be blocked for the rest of the day.

it could in theory be done with a 555, but it would be extremely hard to make the 555 have a long enough delay to block the signal all day. it would also require a very large capacitor. you could definetaly do it with a PIC, and im sure there are other circuits that you could use to give a long delay like that.

as i have no experience with PICs, ill let someone else handle that part for you.

 

[Roff]

You don't need a monostable to hold it off, you just need one to hold it on for a few seconds. See below.
The Schmitt trigger gives a fast negative edge when sufficient light hits the photocell. This edge is differentiated by C1 and R1, and triggers the 555 monostable. The monostable pulse width is adjustable to about 10 seconds max. You can make it longer by increasing the value of C2. It will not fire again until the light level drops well below the threshold, and then rises again to the threshold - generally next morning, unless you have an eclipse or a really dark cloud pass over.
The optional LED is mostly for troubleshooting. It will be a needless drain on your battery, if you have one. An LED and resistor from 555 output to GND might also help in troubleshooting.
If you don't have a CD40106, but you do have another 555, you could use it as a Schmitt trigger instead.
BTW, I haven't built this or simulated it, so it may have errors. Hopefully, some of the other trolls here will review it and catch any mistakes.

 

[zachtheterrible]

purely brilliant ron :lol:

 

[djTopcat]

working circuit

Thanks Ron H (electronics God) Your circuit works great. Ref (Rooster oneshot2.gif) I breadboarded it, and it worked the first time. The circiut kicks on at dawn for about 20 sec. and then turns off. Just enough time for the rooster to do it's thing. Must say, the nieghbors arnt too happy though.

 

[Roff]

Re: working circuit

Thanks Ron H (electronics God) Your circuit works great. Ref (Rooster oneshot2.gif) I breadboarded it, and it worked the first time. The circiut kicks on at dawn for about 20 sec. and then turns off. Just enough time for the rooster to do it's thing. Must say, the nieghbors arnt too happy though.

djTopcat, thanks for the feedback.