# Construction of a Timer circuit - Help

Discussion in 'The Projects Forum' started by sabharish, May 4, 2008.

1. ### sabharish Thread Starter New Member

May 1, 2007
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Hi...I need to construct a circuit which completes a circuit in a specific time; for example, llike making an LED glow after 2 hours or anyother time period given by us. Whats the way for doing this project?

Thank you!

2. ### Wendy Moderator

Mar 24, 2008
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The old 555 would do it, how precision do you need it? It can be made adjustable, or you can calculate the value, but 2 hours is a long time to wait if it has be pretty close. It is, however, an extremely simple circuit. Otherwise you'll need something more digital, which does the precision much better, but has a higher parts count.

3. ### mik3 Senior Member

Feb 4, 2008
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Another timer is the ZN1034 which you can achieve time delays up to several days.

4. ### sabharish Thread Starter New Member

May 1, 2007
9
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I want the circuit to be accurate and the application is like completing the circuit after a given time and cutting it off after a time interval and this should happen as a cycle. Will the above timers ZN1034 and 555 does this?

5. ### Wendy Moderator

Mar 24, 2008
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A 555 can do it, just not with accuracy. It is repeatable however, in the sense it will take the same amount of time twice.

From what you're implying (if I read your post correctly) you want something more like a digital watch with an alarm, accurate to within a couple of seconds. Does this sound more like what you're after?

It would help if you gave us a description on the application for this timer.

6. ### sabharish Thread Starter New Member

May 1, 2007
9
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The application is Switching on and off a Motor at a given time. And its something like a digital clock stuff with an alarm..

7. ### Wendy Moderator

Mar 24, 2008
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You can buy very nice appliance timers that plug in the wall and have 8 or more programmable on off times, including daily functions, for under \$10. They have a solid state LCD timer that is actually a clock, so even if power goes off they keep their time. More what you're looking for?

I use one to turn my BBS on/off by turning the modem on/off, and have used it for water pumps during home emergancies.

8. ### sabharish Thread Starter New Member

May 1, 2007
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Oh...Is there any specific brand?

9. ### Wendy Moderator

Mar 24, 2008
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Nope, I have a Timex, an Intermedic, and have had several other brands, none the same. It threw me when you mentioned the LED, as these are all AC power controllers. They are pretty common, and are available from all dept. and hardware stores. Just check the programmability before you buy it. They plug into an outlet and have an outlet out. You could connect one to an AC relay if you need to make or break a switch for higher power ratings or if you need to turn DC on/off, but they will drive a lightweight motor by themselves.

In one of my previous careers I had a machine that needed to cycle on for 1 hour a week to stay working smoothly, I wound up using something similar to make it happen, wired a relay across the on/off switch. It was used by engineering about once every 3 months or so. Sometimes it is better to use off the shelf, much cheaper and more reliable.

Last edited: May 13, 2008
10. ### sabharish Thread Starter New Member

May 1, 2007
9
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Thank you much for the information .

11. ### Wendy Moderator

Mar 24, 2008
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If you needed the DC function I suspect these suckers can be scavanged pretty easily, I opened one for a look see, pretty basic.

May 13, 2008
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