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I'm basically trying to keep a light on for a period of time then off 4 a period, would a NE555 IC + circuit do the job? Answered


There used to be a device called ZN1034e which was an oscillator feeding a 12 stage counter which would give you looooong delays like this . . . but they don't make them anymore.

With this long a delay you 're going to have problems with setting the period initially, and also from temperature drift of the oscillator once you have got it right. You really need an RTC (real time clock) chip.

I think the much much simpler solution here would be to get yourself a plug-in electronic timer for a couple of pounds / dollars, set the on and off times you want then plug in a wall-wart transformer to drive the LEDs (with suitable resistors).

As an aside, have you looked into the lighting requirements for your plants?  From what I've read, it's pretty difficult to get enough power at the right wavelengths to keep them healthy with LEDs.  (This goes especially for a certain fast-growing resinous plant which is quite often grown indoors under lights ;¬)

Thank you for your research, I'll be using 20 super bright red L.E.D.'s and 5 blue in series with a voltage regulator I built from this site, It's just a test for now and will be growing just a small strawberry plant to see if it can receive enough light to grow to a healthy stage, I see hourly delay times are quite complicated as far as building timer circuits for them go, I may do as you suggest and buy a timer, would of loved to of built it, but I think it may be beyond my technical knowledge, I built the voltage regulator with no problems though.

I'll see if eBay have some cheap timers, but will still research cyberpageman's suggestions.

Thanks again.

Strangely enough, I've just built exactly what you're looking for, but mine was a climate and lighting controller for a vivarium.   Our chameleon needs light for 12 hours a day (UV and heat) and may need additional heat at night if the room temperature drops too far.  His enclosure also needs spraying with water a few times a day to keep the humidity up.

I built a circuit with a PicAxe microcontroller chip, a crystal controlled RTC chip, a driver and 6 relays.  With the RTC I can accurately control each function.  The UV comes on 15 minutes before and goes off 15 minutes after the main light, to give a dawn and dusk effect.   A temperature sensor chip in the enclosure monitors the temperature and turns on a heating mat if things get too cool overnight.   The sprayer is 12V driven and is a car windscreen washer pump with tubing to a micro sprinkler nozzle.

I made this in a hurry so didn't take photos for an Instructable at the time, but when I get the chance I'll take photos of the finished article and present it as a slideshow with a circuit diagram.  It really is quite a simple circuit. 

 Agree with AndyGadget, a 555 timer would work.  There are several Instructables that tell how.  Search "led 555 timer" for ideas.

Oh, sorry Kye37, didn't realize you needed hour times.  From what I read the NE555 is only good for a half hour, or about an hour unreliably.  I  found a page describing circuits with much longer times.  The author gives his home page at the end, and he would probably answer a question.  Hope this works for you.

Quote below from  http://www3.telus.net/chemelec/Projects/Timer/Timer.htm

Two of these CD4541B's connected as a series circuit with one driving the other, with the above values, could create a delay of: 60.8 times 60.8 or 3,696.6 Minutes, which is 61.61 Hours.

1) Use a CD4017 "Decade Counter" to give you anywhere from 1 to 10 times this Time.

2) Use a CD4018, "Divide by N Counter". Divisions up to 10.

3) NEED REALLY LONG TIMES, Use a CD4059, "Divide by N Counter", &nbspAllows for Any Division between 3 and 21,327. &nbsp
Therefore, using this chip and the CD4059 timer of 60.8 minutes &nbspcould give 60.8 times 21,327 = 1,296,681.6 minutes or about 21,611.36 hours or about 900.5 days, or about 2 1/2 years.

I appreciate the time and research you took to compile your reply, it's helped a lot, I will look into it to for sure, for now I will add AndyGadget's reply for the best answer only because I'm not the most technical person when it comes to building big circuits, I but will see if your method will be cheaper.

Thanks again.

Probably yes, but could you give more information :-
What are the on and off periods?
What type of light? 
Does it turn on and off continuously, or is it triggered by something? 
If so, what?

I'll be using the timer to leave the lights on for about 18 hrs or so then off  for about 6hrs and will be using a string of LED lights in series for growing plants indoors, would love to be able to re program the timer to change to on for 12 then off for 12 also during the flowering period of the plants, if its possible with a NE555 IC.

I did a bit of research on the 555 ic and most say its only really used for short timing periods seconds to minutes, I then came across the NE555D IC the specs say it can time from minutes to hours but cant find anywhere how many hrs it can time for, I have a feeling for some reason that its not going to be able to time many hrs eg. 18hr on and 6hrs off like I need it to do, I hope I'm wrong.