# Timer control

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#### P.Samuthira Pandi

Dear All

We want a timer to automatically switch ON and OFF of our office power supply (8 AM and 8 PM). Presently we are doing manually. If You have some idea on this please send me the details of the timer and other accessories requirement.

P.S.Pandi

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#### Matthew Hyatt

P.S.Pandi

You can buy sprinkler timers or other suitable timers for around $20-$50 USD, if you require a larger load switched you can use this timer to control a contactor. You can even get a suitable timer by doing a little research on the internet,

http://www.digikey.com
http://www.newark.com

look up 24 hour timers
set up a PC to run with X10 hardware

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#### Bob Peterson

There are any number of ways to do this, ranging in simplicity from a simple clock timer you could buy from your local electrical supplier (something like what is used to turn parking lot lights on/off) all the way upto programmable building control systems.

I am curious why you would want to turn the power off altogether in the first place.

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#### Michael Griffin

Re: Turning off power in an office automatically.

You should be able to find time of day timers at a local hardware store or electrical supplier. These are common items. However, there are more sophisticated devices which are probably more closely intended for your application.

You can get motion detectors to control the lights. These install in place of the light switch or in the ceiling, depending upon the size of the room. The motion detectors automatically turn the lights off when no motion has been
detected for a period of time (e.g. when no one is present in the room), and automatically turn the lights back on when you enter the room.

There are also programmable thermostats which can be programmed to turn the heating and air conditioning on and off according to time of day. These change the temperature set point (down when heating, up when air conditioning) rather than just turning the heat off, as you don't want to freeze your water pipes over night.

Between the motion sensors for the lights and the programmable thermostats for the heating and air conditioning you will have accounted for the bulk of your
energy use. These items are sold as energy saving devices, and are quite common and not expensive. They are quite commonly used in offices, and the programmable thermostats are often found in homes as well.

For your computers, you should be able to turn them off manually, or at least set them to automatically go into low power mode (monitor and hard drive off) when not in use.

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Michael Griffin
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#### Meir Saggie

How about a simple mechanical (rotary dial) or electronics Time Of Day (even weekly) timer and an appropriately sized contactor?

Just make sure the time and contactor are not switched off as well.

Meir

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#### Yogesh

Dear Mr. Pandi,

Plz contact me for timer details and suppliers. I hope your application is lighting ON-OFF.

Regards,
[email protected]

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Regards

cww

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#### Aows J Ahmed

Dear Pandi

What about useing NE 555 multivibrator, you can use the monnstable moode with Time on =12 hours and before that you have to use a logic circuit as timer to provide the starting pulse for the 555 and the out put of 555 it must be inverted (use inverting amplifier 741 op Amp) then with useing of driving cct. you can add a relay connected directly to the office power and controlled by the output of the driving cct. for any questions send me e-mail.

Aows J Ahmed

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but how to generate a starting pulse to 555 of 12 hours duration?

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#### Curt Wuollet

The best way to do that with a 555 is to use it for a much shorter period and use a divider chip. You can time for extremely long periods with the 555 but it requires very low leakage caps and long
term stability is questionable as a few microamps leakage will really mess things up. It's also most inconvenient to adjust when you only see results twice a day.

But once you have the divider, it's much smarter to divide the line frequency as your timebase as it's stable and typically corrected to very good accuracy in most locations. Of course this brings up the option of simply using one of the many extremely reliable and inexpensive synchronous motor timers available
everywhere.

regards
cww