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Project Help and Ideas » Detect Physical Light Switch settings

April 08, 2010
by Foundry
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I've got a need to detect when a physical light switch has been turned on. Is this something that can be accomplished with the nerd kit? Thanks in advance for any help.


April 10, 2010
by Hexorg
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Well I can think of several ways. with some - you'd have to connect to the actual wires of the light switch curcutry - be careful though, I'd disable the power at the main house switch fist before tinkering with household electricity. You can rectify alternative current with a diode and then lower the voltage to a +5V with a voltage drop bridge.

April 10, 2010
by Foundry
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Thanks. I'm still working my way through the instruction manual, so I'm hoping in the next month or so to take this on.

April 10, 2010
by mrobbins
(NerdKits Staff)

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Hi Ryan,

Just wanted to mention that depending on what you're ultimately trying to do, detecting the actual ambient light level might be easier than determining the physical position of a switch. Detecting the light level (whether a room's light is on or off) is probably a simple two-component circuit, with a photo-sensitive element (photoresistor, photodiode, or phototransistor) plus a resistor.

However, if you're actually using the switch to control something else, or need to know about the switch position even if the light is broken etc., then you may need another mechanism. What exactly are you trying to measure?

Welcome to the NerdKits forums!


April 11, 2010
by Foundry
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Here's a little background on what I'm attempting to do....

At my company, we have door switches on the two bathroom doors so that when a door is closed the light turns on in the main office so that you can see a bathroom is in use. This works well for the 5 people in the main area, but we have 30 people spread throughout other rooms in the office who can't see these lights. I'd like to put together a system where using Nerdkits, I can determine if a light is on or off and make this information available on everyone's computers. We have an internal instant messaging system that we're already using for operational alerts (uses the XMPP / Jabber protocol).

Any ideas appreciated.

April 11, 2010
by mcai8sh4
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Nice idea - I'll have a think about how I'd go about it... if I have any good thoughts I'll be sure to let you know.

April 11, 2010
by Farmerjoecoledge
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Mirrors! No really, a photoresistor the kind that comes on with light. That "on" signal can be relayed to the nerdkit and then to the rest of the system. Just an idea, you'ld have to figure out the rest.

April 11, 2010
by Foundry
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Would ambient light be an issue? We have a number of light cans near it.

May 05, 2010
by n3ueaEMTP
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Would a small signal relay in parallel with the signal light work as well? The normally open contact of the relay could serve to pull a pin low similar to that of the traffic light project when the walk button is pushed.

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