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[on:]

Hello,
i got an arduino duemilanove and a led spot want to power them.
These are the LED spot specs:

mA test.:    200 mA
mA typ.:    500 mA
V typ.:    6,5 V
V max.:    8,0 V
Watt:    3,25 W

Is it possible to power them with one power supply? Which trafo do I need? How can I turn the spot with on/off with the arduino? I need a relay, or? Which kind of or doesn't this matter?
Thanks

[Reply #1 on:]

Connect an 8V power supply of about 700 mA to the power socket of the Duemilanove and use the 'Vin' pin (directly connected to the power socket) to power the LED.  You will need a transistor+base resistor, a small reed relay (5v, <40mA coil), or a logic level MOSFET to switch the LED on and off.

For an NPN transistor or N-Channel MOSFET you connect the Vin pin to the + side of the LED and connect the - side of the LED through the device to Ground.  For a relay it doesn't matter if the relay contacts go on the Vin side or the Ground side of the LED.

If you want to control brightness with PWM you shouldn't use the relay because it probably doesn't switch fast enough.

[Reply #2 on:]

Thanks.
I want to built a ethernet remote control which will be mounted to the ceiling.
Will it switch fast enough for irda-signals?

[Reply #3 on:]

If you use a transistor or MOSFET it should be plenty fast enough.

[Reply #4 on:]

Thank you very much!

Which Mosfet do i need. I find just some from 50V ... 100V ... etc. The lowest V is 50. Will this work or stands the volt for the used volts? Or for the max volts?

Will this work?
http://www.ebay.de/itm/5-Stuck-MOSFET-n-channel-MOSFETs-BUZ11-BUZ-11-/270667454648?pt=Bauteile&hash=item3f050998b8

[Reply #5 on:]

The problem with the BUZ11 is that the low "on resistance" (Ron) is specified with a gate voltage  (Vgs) of 10V.  Since the logic output is 5V you might get enough more resistance that it can't handle the current. Higher voltage drop = higher power dissipation at a given current.  You should look for a Logic Level MOSFET: one that has a very low resistance with a gate voltage (Vgs) of 5V (or less).

[Reply #6 on:]

Mh which one would fit?
http://www.mikrocontroller.net/articles/MOSFET-%C3%9Cbersicht#N-Kanal_MOSFET

[Reply #7 on:]

Sorry, I don't read German well enough to understand the specifications.

I tried Farnell's UK site and found these 226 N-channel MOSFETS that have Ron specified at 5V or less gate voltage.

 http://uk.farnell.com/jsp/search/browse.jsp?N=204245+110158844+110137572+110169481+110127240+110029860&No=0&getResults=true&appliedparametrics=true&locale=en_UK&divisionLocale=en_UK&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=204245+110158844+110137572+110169481+110127240&mm=1002572%7C%7C,1002889%7C%7C,1000363%7C%7C,&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D204245%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26divisionLocale%3Den_UK%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D204245

The German results seem to be the same:

http://de.farnell.com/jsp/search/browse.jsp?N=204245+110158844+110137572+110169481+110127240+110029860&No=0&getResults=true&appliedparametrics=true&locale=en_UK&divisionLocale=en_UK&catalogId=&skipManufacturer=false&skipParametricAttributeId=&prevNValues=204245+110158844+110137572+110169481+110127240&mm=1002572%7C%7C,1002889%7C%7C,1000363%7C%7C,&filtersHidden=false&appliedHidden=false&autoApply=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D204245%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26divisionLocale%3Den_UK%26catalogId%3D%26skipManufacturer%3Dfalse%26skipParametricAttributeId%3D%26prevNValues%3D204245

Starting there you can select a MOSFET that has the current switching and voltage capability you need, a convenient package, and a reasonable price.

[Reply #8 on:]

Ok, then i will buy this:
http://uk.farnell.com/fairchild-semiconductor/rfp30n06le/mosfet-n-logic-to-220/dp/1017798?Ntt=1017798

You will need a transistor+base resistor, a small reed relay (5v, <40mA coil), or a logic level MOSFET to switch the LED on and off.

Do I need something further? Do I "transistor+base resistor, a small reed relay" just if I don't use a MOSFET. I don't need an resistor for my led, or?

 

[Reply #9 on:]

I expect the LED spotlight already has current limiting resistors (or current regulator) suitable for the 6.5-8v power supply.

Someone wit more electronics experience than me recommended a 110 ohm resistor between the Arduino pin and the Gate of the MOSFET to protect the Arduino from excessive current draw.  Shouldn't be necessary but couldn't hurt.

[Reply #10 on:]

Shouldn't be necessary but couldn't hurt.

It is because a FET's gate is a capacitor and when it is discharged can draw an infinite amount of current for an instant. So to protect the output you need a resistor.