Use 555 to switch led off for 8 hour delay?

[ponjovi]

I'm trying to learn about different electronic timers for a project I have (and learn about electronics in general). I want to run a low-power LED lamp (~3V, 250 mA) that is always on, except that it shuts off every night for 10 or 12 hours (user adjustable).

Q1: Can the 555 timer do delays for that length of time? If I understand correctly, they use resistors to determine the time delay, usually of seconds, and this length of time might require too many/big resistors?

Q2: If so, any suggestions for a component that would allow user to toggle between different modes of 10 hour delay vs. 12 hour delay?

Thanks, any suggestions much appreciated!

 

[George]

It is my understanding that that amount of time is not possible using just the 555timer. The problem is capacitor leakage. One way around this is to use a counter and have the light run off that and not just the 555timer. You can use a CD4060 counter, I will look into this more and give you a schematic if you want. If anyone else hare has a better idea or a schematic already made please post it.

Regards,

George

 

[ponjovi]

Thanks for the response, George. I looked around at the 4060 and it does seem to offer time delays up to 12 hours, which is perfect.

In terms of the schematic, what we're trying to do is actually build this timer function on top of a solar-powered garden light (the kind with a photosensor to automatically shut off). We have the solar garden light circuit already done and produced; it uses a Zetex ZXSC310, a 2V solar PV, and single cell 1.2V NiMh battery. What we're trying to do now is design a new circuit that includes the timer function....

 

[George]

I am guessing you want to keep this timming circuit as small as you can. Do you have the ability to make it out of all surface mount components? That would keep the size as small as possible. What is going to be your power source for the timmer circuit, will it be the 1.2V Batt? If thats the case you might want to think about stepping it up to at least 5V, I would have to read the 555 and 4060 specs on power requirments and ways around low voltage like you have already. Because it is just a garden light I am thinking you don't want some bulky package attached to it just for the timmer. Just a few thoughts I wanted to send you, let me know what you think.

George

 

[George]

Here is a link to a long time duration project I found, it does not state the time but worth looking at. http://www.talkingelectronics.com/te_interactive_index.html

 

[ponjovi]

I am guessing you want to keep this timming circuit as small as you can. Do you have the ability to make it out of all surface mount components? That would keep the size as small as possible. What is going to be your power source for the timmer circuit, will it be the 1.2V Batt? If thats the case you might want to think about stepping it up to at least 5V, I would have to read the 555 and 4060 specs on power requirments and ways around low voltage like you have already. Because it is just a garden light I am thinking you don't want some bulky package attached to it just for the timmer. Just a few thoughts I wanted to send you, let me know what you think.

George

Yes, definitely want to eventually make it out of all surface mount. The power will be either a 1.2V battery or 3.6V li-ion, if the former then we'll definitely need to boost to drive the LED.