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Apologies for the simple question, I really couldn’t find any help online with this as when I kept searching, the results had lights that had way too much voltage compared to what I need.

So I have a simple light decoration that requires around 3v and comes with a battery pack to power it (2AA batteries) and I took it apart and was able to connect them via a breadboard to test if is all working.

How do incorporate the Arduino into it so that I can switch the lights on through the Arduino? A lot of the small voltage videos I saw were just simple connecting 1 LED through a digital pin but that’s not enough current for the lights I have and I’m not experienced enough to find myself a solution so help would be greatly appreciated.

For little more info, the 3.3v and 5v pins my Arduino (uno) are already taken up.

Also, I’ll be turning the lights on and off with an IR Remote which I’ve already programmed to a servo that’s powered through the USB supply (5v) and the IR Sensor is connected to the 3.3V.

Sorry if the question was badly worded.

  • It all depends on the simple light decoration. What is it? Can you show a photo? Do you have a schematic of it? What kind of leds are used? and so on. – Jot Jan 14 '19 at 21:41
  • imgur.com/a/TgPQBDZ imgur.com/a/b0l1isT - It’s a small shelf decoration in the shape of ‘&’ @Jot – Josh Jan 14 '19 at 22:11
  • No @gre_gor, the dude there is calling for a 12v lightbulb. – Josh Jan 14 '19 at 22:14
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    the 3.3v and 5v pins my Arduino (uno) are already taken up .... no they are not .... run a jumper over to the breadboard so that you can make multiple connections – jsotola Jan 14 '19 at 23:20
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    the comment was about pin availability since you said that you have no more pins for 3.3V and 5V ...... power availability is another issue ..... do not power a servo from the arduino – jsotola Jan 15 '19 at 1:44
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I think I managed to make a little circuit that should prevent you from burning up your Arduino.

Safely driving MOSFET from Arduino

From what I read you shouldn't connect MOSFET directly to Arduino. Imagine that MOSFET has a little capacitor inside it, and in the beginning that capacitor can take such high current that actually can burn the Arduino pin. Instead you use a simple NPN transistor (with 100kohm resistor) as a "switch". The NPN can survive much higher current, and it will not strain the Arduino pin.

When I simulated this setup using the default "blink" sketch the light bulb was lit when PIN13 was HIGH. Just note that there always is a small voltage drop (think of it as a resistor inside the MOSFET) and it can make the MOSFET get a little warm. In your setup it should not be a problem, but in some cases it's nice to screw a radiator on the MOSFET.

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  • Thank you so much for the reply and schematics. I’ll have to buy a mosfet as the Arduino kit I have didn’t come with one, and then I’ll test it out. Thanks again! – Josh Jan 15 '19 at 16:45
  • Before I purchase mosfets, as they only come in packs and I will likely never use them again, will anyone of these be sufficient? imgur.com/a/U15yVXi (They come with my kit?) – Josh Jan 15 '19 at 19:12
  • These are not MOSFETs. These are BJT transistors of the NPN type. Since your light decoration will probably not draw much current It's quite possible that you will be able to use just them (just remove MOSFET from my design) Please experiment with different designs in Tinkercad. – Filip Franik Jan 15 '19 at 19:33
  • After taking out the mosfet, the light turned on. One problem I have before I build the actual circuit is the resistor. I have never decided my own value for resistors before so I don’t know what to do. You mentioned 100k for the mosfet but not that I’m not using it surely I don’t need a 100k resistor? Seems way too much. Also - huge thanks for introducing me to tinkercad. This will help me for tonnns of projects! – Josh Jan 15 '19 at 22:24
  • MOSFET to work properly needs to be discharged to be opened (that imaginary capacitor is inside) so when the NPN (electronic switch) is "opened" that 100K resistor discharges the MOSFET. But when NPN (electronic switch) is "closed" part the current goes into the MOSFET (charging the imaginary capacitor), and part goes through that resistor. The higher the resistor value the less current is wasted that way (but slower MOSFET discharge) But if you removed the MOSFET you probably don't need to discharge anything, and it's possible that your lights will work without the resistor. Experiment. – Filip Franik Jan 16 '19 at 0:01

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