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Meta objective: I want to pull up a TV with a winch, when the TV is turned off. I can already move up and down the TV invoked by my controller (Arduino Nano). The physical push-sensor stops the winch automatically. Good so far.

Objective of this questions: I don't want the guest to push an extra button to make the TV go up or down. There is an indicator when the TV is used and that is the Watts that are going through the 220/230V cable to the TV. If amperage is high, I instruct the winch to let the TV down (viewing position). If it is low, I pull the TV up.

See the sketch for a general idea.

enter image description here

Now, I'm not an electronics engineer. My question is: 1) How can I measure the high amperage (or watt) of the 220/230V cable and give that value to my 5V-controller (Arduino Nano). With my little experience I cannot think of an electrical component that could do that. However, there certainly must be a way to detect the big difference between 300 mili watts and 75 Watts. Nice if someone could point to a real component so that I could read up on that component.

2) Can one achive my meta objective without a controller? (This is nice to know. I'm totally happy if questions 1 is answered thoroughly.)

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    \$\begingroup\$ You might like to look at Hall Effect current tranducers \$\endgroup\$ – David Oct 22 '14 at 7:37
  • \$\begingroup\$ Are you sure you're going to be able to turn the TV on when it is in its raised (and presumably hidden) position? \$\endgroup\$ – Dave Tweed Oct 22 '14 at 11:47
  • \$\begingroup\$ @DaveTweed yes, It's just at the very top of this super high ceiling. \$\endgroup\$ – feder Oct 22 '14 at 17:45
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I may earn downvotes for this, but I would NOT recommend dealing with 230V when having no experience!

Anyway, of course it's possible what you want to do. Not the cheapest, but maybe the safest way would be using a current transducer like this http://www.lem.com/docs/products/lts_6-np.pdf
With that, you can pull the insulated phase wire through the hole, and get a voltage proportional to the current (the exact formula is in the datasheet) at the output to be measured by your Arduino.

Another, less risky approach without 230V:
A further indicator when the TV is off is when you push the "ON/OFF" button on your remote control.
It's most likely an RC5 or RC6 code. Connect an IR receiver to your arduino and implement a RC5 decoder to know whether one turns the TV on or off.

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    \$\begingroup\$ No, you don't get a downvote for that! Security is most important. (However, I studies these electric dangers for a few weeks now. I'm on the save side and would never operate on a charged 230v line.). A transducer. Nice. Remote IR receiver, why not. However, the drawback of this solution is, that you don't know the true state (Is TV off or not? In case the IR signal is missed because the quality of the sensors are different). \$\endgroup\$ – feder Oct 22 '14 at 8:49
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You can buy a master-slave power bar/surge arrestor that will provide mains power on a slave outlet when the master is detected drawing power.

(image is of a US/Canada standard 120VAC/60Hz bar, but such devices should exist in your market).

http://www.amazon.ca/APC-P8GT-Power-Saving-SurgeArrest-Protection/dp/B002K8S2J6

Then you can plug in a standard safety-agency approved "wall wart" supply into a slave outlet and use that to either directly control your winch circuit or derive a logic signal to feed to your processor.

With this approach, nothing touches the mains that is not properly isolated and safety-agency approved, yet cost is reasonable.

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For those who are looking or hall effect sensor that can be hooked immeadiately to a controller like Arduino, search ebay for "5A Range AC Current transformer module Current sensor module". Of course this is for hobby projects only!

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