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I have looked on stack overflows forum and can't find the answer to my 2 questions. So here they are.

  1. Can I power a motor using an arduino uno with just the outputting to the motor like I can with a led without having a motor shield?
  2. This is based on number one but let's say the answer is yes for now until I find out the answer to question number 1. I have a max of 3 volts that my small dc motor can take and I know the arduino out puts 5 volts, so that means I am 2 volts over the limit by simple math. I have about any resistor type you can think of, so which one will I need to put into my circuit? I am confused on why I can't find anything on converting 2 volts to ohms for the resistor value.

Thanks in advance.

Sean.D
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Powering your motor right from the output is typically not advised. The digital pins on Arduino can only souce a small amount of current. Typically far too little to drive a motor. But, it depends on the motor of course. More important than voltage of your motor is knowing how much current is needed to drive it.

For your resistor question, look into voltage dividers using resistors.

Mike

Michael Bedford
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  • The voltage on the motor like I said in my post is 3v and the output of an arduino is 5v so I have 2 volts over. It is a small dc motor. I have never heard of voltage dividers as I just looked it up. So you apparently put 2 resistors in series. But which one? Can you elaborate more? How much resistance is all I need to know? – Sean.D Jan 01 '17 at 02:46
  • Also that divider is input when I am outputting and how is the circuit set up without adding more voltage to it? If I wire in series there will be a positive and a negative end going to one place on the arduino and not 2, so your answer is not very helpful no offense. – Sean.D Jan 01 '17 at 02:53
  • Sean, the motor voltage does not matter when you need to figure out if your arduino can drive it safely directly. What is the current requirement of the motor at max rpm, at 3vdc? It should say in the data sheet for the motor. You really need to know the current. It is also important for the voltage divider so you can make sure we have resistors that can handle the heat dissapation. What are your resistors, 1/8 watt? There should be a voltage divider calculator if you google that. – Michael Bedford Jan 01 '17 at 02:59
  • By the way, the Uno can only safely source or sink 20mA of current on digital pins. If your motors current requirement is close to that or more, you cannot drive the motor directly. 20mA is a very small amount of current so unless the motor is extremely small, you likely cannot do it. – Michael Bedford Jan 01 '17 at 03:07
  • And here is a good calculator http://www.ohmslawcalculator.com/voltage-divider-calculator – Michael Bedford Jan 01 '17 at 03:08
  • Here is the motor specs. – Sean.D Jan 01 '17 at 03:41
  • http://www.ebay.com/itm/like/331512818185?lpid=82&chn=ps&ul_noapp=true i accidently clicked enter so sorry about the 2 post. – Sean.D Jan 01 '17 at 03:42
  • That said, I looked up the data sheet for you since the ebay post at least has the part number. Here are the specs. Radio Shack Metal Gear 1.5V-3VDC Motor (273-0258)Voltage Range: 1.5-3VDCCurrent: 0.18-0.25A at No Load; 0.70A +/-15% at Max EfficiencySpeed: 8700 RPM +/-12% at No Load; 5800 RPM +/-12% at Max EfficiencyShaft Length: 38mm (1.5 in)Shaft Diameter: 0.0787mmOutput: 0.31WTorque: 5.3g/cm – Michael Bedford Jan 01 '17 at 03:52
  • That means, you cannot drive that motor safely, directly. You need other circuitry or to be easy on you, a moyor shield. Also, the link I sent you clearly show voltage dividers, how to wire it and the calculator should you need it, for future reference. – Michael Bedford Jan 01 '17 at 03:53
  • Actually I saw the specs, and I was a little uneasy because of the 2 different amps, so I did not know which one to put in. Anyways, I will have to get a shield then. I actually did have to do some work to even find the specs because I got it at radio shack and they did not give the specs online. Good old ebay had it though. I did look at a website for the divider and I commented back saying how can I do series into that with 2 wires into one with positive and negative. Anyways, thanks for your help. – Sean.D Jan 01 '17 at 04:09