15 minute Timer that it triggered by an event.

John Bobowicz's picture
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Joined: Jan 03, 2017
15 minute Timer that it triggered by an event.
January 3, 2017 - 7:41am

I need the ability to have an AC device turn on when my garage door open and automatically turn off 15-30 minutes later.

We have a problem with mosquitos coming in the garage at night when the door opens and then get trapped in the garage only to make it inside the house when someone goes into the garage for anything.  I have a bug zapper that I can plugin and hang, but I want it to turn on when the garage door opens and turn off after some period of time, after the garage door opener light goes out.

I think this is two circuits.  Any help is appreciated.

B.Aswinth Raj's picture
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Joined: Aug 16, 2016
okay, now we have to turn on
January 3, 2017 - 12:27pm

okay, now we have to turn on and off an AC load.

For this we will need a Relay and its driving circuit. The Relay should be selected based on the Wattage of your AC Load(Bug Zapper).

Now, lets see how to turn it on and off. I assume you garage is dark (or partially dark) when it is closed and light comes in when you open your garrage door.

So, lets use a LDR (Light dependent resistor) to know if your  garage door is open or close.  When it is open more light will come in and the Resistance of this LDR will decrease sensing that we can turn on your AC load by triggering the Relay and also start a timer. The Timer can be a 555 timer IC when can be set to release the Relay after 15-30 minutes after being triggered. 

I have assumed that you have some basic skills with electronics.

Thanks!!

John Bobowicz's picture
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Joined: Jan 03, 2017
How does the LDR get powered?
January 3, 2017 - 8:09pm

Thanks!  I have used relays in the past for turning exhaust fans on and off with a thermostat, so that makes completed sense.

The relay has high and low voltage and the low voltage is the switch to complete the high voltage switch.  If I'm using a LDR to provide a low voltage load to the relay and timer, how am I powering the LDR?  I haven't worked with LDRs.

I can definitely isolate the LDR so that it's only exposed to it is the light from the garage door opener, that turns on when the garage is open or closed.  This way the bug light will be turned on whenever the door is open or closed and the timer will keep it on for a period of time after the garage door opener light turns off.

B.Aswinth Raj's picture
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Joined: Aug 16, 2016
Hi John,
January 4, 2017 - 6:15am

Hi John,

You have to make your own power source or buy one here. Because you have two things to be powered here. One is your Relay and other is your LDR Circuit. I would suggest you to buy a 12V 1A DC Adapter, 

Use it and build your circuit, The circuit will have a Relay Driver (transistor and diodes) to turn on or off the Relay with 12V power source.

And you can use the LDR as a potential divider. That is, one resistor will be constant value resistor and the other will be LDR(Variable resistor), Use the 12V as input voltage and read the output voltage across the LDR, So when the door is opened the resistance of LDR will decrease and voltage should also decrease.

Now experiment with this output voltage based on your lighting condition and decide when to trigger the Relay, once you get that just figure out a way to connect his output to the relay driver circuit, mostly i guess a simple op-amp in differential mode will do the trick .

Hope you get my point!!