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Garage door sensor, two LED, circuit design help

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Aug 24, 2009
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door sensor circuit

I'm looking to design a circuit that will tell me, via two (separate red and green, not bi-color) LED. I had some surplus magnetic sensor switches (two wire, open or closed based on magnet proximity to contact) so i had them mounted to the garage and floor.

so here's what i need, if the garage door is open and the sensor switch is in the open or "break" position, I want the red LED to light up. if the garage door is closed and the sensor is in the closed or "make" position, I want the green LED to light up.

there will be three sets of these red/green LED pairs around the house.
I plan to use a A/C wall-wart to power this project with (most likely) a 5v/DC output of around 300ma (I can't think this will need that much power). or should I use lower voltage?

not sure if this is important or not....
there will be approx 20 to 40 feet between the main circuit and the door sensor.
there will three runs to the LED's will be 10 feet, 20 feet and 40~50 feet.
copper connecting all this is cat-5e. there is a dedicated cable for each run.

I'm pretty sure this is a very simple design requiring a sensor switch, a power supply, two LED's and one or more transistors. not sure about diodes and resistors though. It's has been over 25 years since I sat in a digital circuits class, so i'm very rusty on this stuff.

Thanks in advance

garage door sensor circuit

looks like a simple enough design, i'll have a close look at it tonight.
couple of questions.

how do i calculate the required ohm-age of the resistors, based on a known voltage? what's the forumla? since I don't know for sure what the specs on the power supply will be.

second, is there anyway to do this without a mechanical relay? hopefully just transistors?

Thanks much,

led circuit


When you know your actual voltage and led type then use this site to calculate the resistor value

Yes you could use transistors but other than it using a few more milli amps of current using the smallest of relays, why complicate things .

Using transistors when your contact switch is 40ft away will make them prone to interference unless you fit extra caps etc.

led circuit design

i think what wp100 refer is relay ,but beekerc's is not. maybe its right name is reed switch. if your Led is not high power ,the switch can control the current directly.

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