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Author Topic: Adjustable current sensor switch for lighted glass shelves  (Read 3029 times)

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gillone

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Adjustable current sensor switch for lighted glass shelves
« on: June 01, 2011, 12:04:47 PM »
well I have this neat AV cabinet with a few devices and each sits on a glass shelf - I installed blue LEDs behind the shelf and it looks cool. I always thought that it will be even better if I could light up just the shelf that the device is on. To do this I could open each device and get a relay hooked up from inside ... etc.
Another way would be to use a current sensor on the power cord of each device and when the device is turned on the LED on the shelf will turn on. I did find a few diagrams but main problem is that all devices have a stand by current and it's different for each device (sat receiver, amp, xbmc PC etc) so each current sensor will have to b adjustable to "see" the diffence between stand-by and on. My electronics knowledge is limited to "build from instructions" so I could use some help.
I thought that I could install everything inside a power strip that already has a power plug and leds aligned with each shelf.
well - I hope you guys find this ideea fun and come up with a solution - thanks

kam

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Re: Adjustable current sensor switch for lighted glass shelves
« Reply #1 on: June 02, 2011, 16:46:33 PM »
I would go for the "open and wire from the inside" solution for 3 reasons: 1. reliability of operation, 2. Ease of implementation and 3. Price.

The current transformers are expensive equipment to use.  If you want no matter what to use them, then you only have to hook them on a comparator. Here is how it is done. A current transformer has 2 wires as an output. A resistor must be connected to these outputs. The value depends on the transformer, make some tests. Put different resistors and measure the voltage across them. The voltage across the resistor must increase when the device is turned on. You need to find a resistor that produces usable voltage. For example, anything above 1 volt (when device is on) is ok. Remember that the current is AC, so you need to make it DC with a bridge rectifier. So we have: First wire of the transformer goes to first lead of the resistor and first lead of the bridge rectifier input (AC). Second wire of the transformer goes to second lead of the resistor and second lead of the bridge rectifier input (AC). The output of the bridge rectifier is now a DC voltage. It gets a higher value when the device is on.

The negative (-) output of the rectifier is connected from then on to the power supply (that you must also have) ground.

Then make a comparator circuit. Get a comparator chip (almost any comparator will do). It has a + and a - and an output. Connect the + output to the + output of the rectifier.

Then get a 10K potentiometer. It has 3 leads. The middle one goes to the - input of the comparator, one side goes to the positive power supply and the other to the ground (this is a voltage divider setup).
-END-

The potentiometer sets the threshold level. Turn on your device. Turn the potentiometer until the output of the comparator is high. Then turn off the device. The comparator output should become low.

_pike

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Re: Adjustable current sensor switch for lighted glass shelves
« Reply #2 on: June 03, 2011, 01:22:38 AM »
kam+1
I agree with kam....As your electronics knownledge is limited the best ways of doing this is "inside wiring"Do you usually have your equipment on stand by mode or in off mode???Because that could be a problem to an inside wiring....Another way that just came up to me is to built an infrared receiver that would be able to decode only one button code (the off-on) from each device.... (but you will need an oscilloscope to do the measure,so i finally don't think that it's the best solution to you....)

gillone

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Re: Adjustable current sensor switch for lighted glass shelves
« Reply #3 on: June 24, 2011, 12:52:31 PM »
Thank you for answering.
I was really hoping for a easy hack like: get these http://www.nktechnologies.com/pdfs/ampflasher_data_sheet_0411.pdf and modify the "factory set" 500mA trigger.
Thanks - I will look some more and post back