Custom "switch" for Emitter-Robot flashlight

tommydonovan

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May 26, 2010
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First off, let me apoligize in advance if this is in the wrong forum. I looked them all over and thought this to be the most appropriate.

Here is the problem I have: I have an led that I'm looking to upgrade. The led was never intended to be a "flashlight" and as such is wired up with very small wires and receives very little current. I'd estimate that it is being driven by approximately 3.0V and 200ma- it's intended to be more of an indicator light, but I need it to illuminate a room. So I disconnected this led and hooked up an XM-L T6. While the new led is brighter, it does not illuminate like I need it to.

So here is what I need: I have access to a 6V battery in this same setup. This battery is capable of providing as much current as I need to run the XM-L. I need a "relay" that is activated by this original small current, low voltage wire that will allow the current from the battery to flow to the new XM-L (obviously this current will be properly resistored to provide the necessary amount of illumination, and to protect the XM-L).

This setup is inside of a robot (with camera/mic/speaker/etc.) that is controlled via the internet. The original led can be activated via web browser and that is why I need that led's wire to activate this relay to turn on a "real light". That way I can drive my robot around in the dark :)

I'm familiar with 12 Volt systems and using relays to make things happen there, but don't know of a "relay" that will activate at such low voltage and current. Thanks in advance to whomever can help me, it is much appreciated.
 

Th232

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Have you considered using a MOSFET on the low side of the circuit?

Off-topic, but depending on how much current you're planning to put through the XM-L, what's your heatsinking like?
 

doktorziplok

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Mar 10, 2011
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i say try using a infrared led. if you'll be driving via webcam you should be able to see the light and keep it dark in real life. most digital camera sensors can pick up IR.
 

CarpentryHero

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Unfortunately I don't have any experience with remote switches. The XML is a good choice for led though, it can handle up to 3 amps, have you considered using the origional circuit and adding buck drivers, consecutive (one into the next)
Its a little beyond me, so I apologize if I'm out to lunch on how to do this. :welcome:
 

tommydonovan

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May 26, 2010
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th232- I would consider using anything that works ;) I'm just not real familiar with mosfets or how they operate. If someone was able to explain it or design me a circuit? Haven't designed heatsink yet but led will be exposed to air and not driven super hard, something like 1000ma probably, just need a couple hundred lumens I think.

CarpentryHero- The original led is very small and the circuit that feeds it is not capable of driving much of anything, hence the need to relay :( Also, I have to make sure not to mess that circuit up as I am definitely not capable of rigging up one that I can turn on via my internet interface lol.

So to reiterate, I need some type of circuit that will allow current to pass from battery to led when triggered by ~3V@low current.
 

Th232

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A MOSFET is, for your purposes, an electronic switch. In an N-channel MOSFET, there are three legs, gate, drain and source. You connect drain to positive and source to negative on the low side of the circuit (so that source is connected to ground or the negative battery terminal). The voltage difference between gate and source is what turns it on and off.

A third of the way down:

http://www.electronics-tutorials.ws/transistor/tran_7.html

is what you need, the image under "An example of using the MOSFET as a switch". In your case, VDD is the 6V supply and +Vin is the 3V wire, you'll have to choose a MOSFET to fit those parameters. There're probably some other good webpages around if you google for them, but that's just what I had on hand.

With the power level, just so you're aware, while 1A isn't very hard compared to its maximum rating there's still going to be enough heat there to burn the LED very quickly without adequate heatsinking, whether or not it's exposed to air.
 
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