Small Building Light Control

Projects General Guidance
1

Hello,
I've been tasked with making an automated light on/off control for a local museum's hangar. The lights are just normal tube lights controlled by a switch like this: http://images.wisegeek.com/light-switch.jpg. However, I'm a bit at a loss as to how to turn the power on/off. I'm told that the connection is a 110V standard US power line. Should I use a MOSFET for this? I don't think the "timer" part of it will be that hard, if I use something like this: DS1307 Real Time Clock breakout board kit : ID 264 : $7.95 : Adafruit Industries, Unique & fun DIY electronics and kits. Does anyone have suggestions on how to turn on/off that power line for the lights?

Any help is greatly appreciated.

Thanks!
Mihir (iluvplanes)

2

A solid-state relay (SSR) is probably the simple answer. Example:

3

Looks neat! Thanks Nick!

4

Hi Nick, So if I use this with the arduino, and I connect it up, if I sent a "HIGH" to digital pin say, 6, and the relay was connected, would that turn on the lights? As in, would that act as a switch for the 110V?

Thanks!
Mihir

5

That's the idea. Thanks for the clarifying picture of what a light switch looks like, by the way.

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Of course you can buy timers that turn the power on and off at intervals, so I assume your project is more complex than that.

6

Yeah...But I need it to turn on/off on only certain days, at different times on those days...

7

If you are not an electrician, you might get into code issues changing the wiring. You might look at using a servo to operate the standard switch, which would allow the switch to also be normally operated when desired. the servo could be attatched to the switch cover plate so it could be easily removed when desired.

8

Honeywell makes a device to do this for you: Honeywell Programmable Light Switch Timers, Automatic Lights, and 7-day Programmable Light Switch Timers. Honeywell RPLS730B1000/U 7-Day Programmable Light Switch Timer (White). | Honeywell Store. No doubt there are others.

9

Instead of SSR, an SPDT Relay https://www.sparkfun.com/products/100 would be sufficient for lights. (upto 5A)
You can actually connect multiple lights through one relay taking care of the current limit.

You need to connect the output of the microcontroller to a simple amplifer circuit before connecting to the relay coil. You could use BC547 and a 27kohm base resistor. Use a 12V Vcc. Output will be inverted. Just use the NC (normally closed) contact of the relay. This way, you don't need to energize the relay coils when the lights are ON.

Done!