Have Arduino uno got enough current for vibration motor ?

[DuncanC]

so you COULD use a voltage divider or an external regulator to step down the 5V to 3.3 and use that to power your motor.

You should never use resistor divider network as a power source.... not only does it waste a huge amount of energy as wasted heat, it also becomes a large problem because depending on current draw and voltage you will likely end up needing power resistors which tend to be more expensive. Plus you will likely not be able to get needed values in large power resistors as they tend to be lower resistances.

If you wanted to use 5V rail your best bet is a low drop out voltage regulator to regulate 3.3V

And 5V rail is not 880mA.  I believe the max rate is 800mA but you will not want to run that high due to heat dissipation issues. And not only that but this is all assuming you have external supply capable of that because USB certainly isn't. It has 500mA max and not all computers are even compliant to that standard.

Clearly a separate 3.3v supply is a much better choice. Lots of people have said that, but the OP insists that he doesn't want a separate power supply.

As a general rule I agree with you about not using a voltage divider for power.  However, in this application the current needed is only 120 mA, and based on my calculations the current wasted is only about 40 mA. Not ideal, but it would work.

The OP doesn't want to add a separate power supply, so I was offering a solution. Not an ideal solution, but one that should work.

Since the current needed is only 120 mA, the OP can get away with normal 1/4 watt resistors. R1 in my circuit will limit the total current to about 128 mA. Actually, I guess I under-rated that, since some current will be wasted to ground.

[wes000000]

but the OP insists that he doesn't want a separate power supply.

At some point if he wants to take his project somewhere where he doesn't have access to a PC he will need a power supply other than USB. So I am suggesting he only use one power supply (but make it capable of handling needed current) and having several regulators attached to it in addition to the Arduino. So one power supply, and two regulators and all his power problems would be solved. I wouldn't be surprised if he can get all that on eBay for under $10, maybe even $5

the OP can get away with normal 1/4 watt resistors

Nope. A current draw of 120mA and a voltage of 3.3V gives .4 watts of power so you would need 1/2 watt as absolute minimum but even that would be pushing it as it would get hot very quickly. So I'd say you'd want at least a watt. And those resistors can get expensive so I go back to the solution of a single power source and two cheap regulators.

Not ideal, but it would work.

I suppose one could make it work but it's beyond non ideal. Because in addition the load is going to add an extra loop to the circuit and additional resistance. As such the Vout will start to change depending on the load ESR. It is really just terrible all around to use voltage dividers as any kind of power source.

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/voldiv.html

[JimboZA]

Here's what the circuit would look like (ugly drawing alert!)

The load should be on the collector.

[Palatis]

Ahh... no!!!

1. the 2 resistors draws 44mA when the motor is off...
2. you'll only get ~2.45v when the transistor turned on.
3. the transistor itself got a Vf, should take that into consideration.

voltage dividers will work with high impendance load, like a 20k/50k ohm divider vs a 600k ohm load, won't work with resistive load.

[Paul__B]

This discussion has passed from the sublime to the ridiculous.

Running a 3V motor from a 5V supply is dead simple - measure the (running) current draw at the specified voltage, calculate the resistor to drop the difference between 5V and 3V at that current, and put that resistor in series with the motor.

This discussion is however just so ridiculous that I will not even do the calculation.

Sure, this will mean the motor is slower to start, but it will not be overloaded and there will be no wastage in shunt resistors.

[jeolex]

Firstly thank you for your all replies. They are full with informations and good ideas.

If I mention about my project, it will be better.

I am a master student in Department of Agriculture. I planned to make a Wheat Grain Counter. So I draw in my mind sketchily and I need vibrator motor, LCD, phototranssitor, IR led and some bottons etc..

I will have a container which is keep grains and when I apply vibration, grains fall down from container to inside of the pipe (pipe has a phototransistor and IR led). So when grain pass through between IR Led and phototransistor, counter increase and show in LCD display. I know it s not a big project but I am new and keen about electronic things.

So I have been successful about counting grains with phototransistor. My next step is applying a vibration and fall down the grains.

Actually I will not use USB power. I just want to one power supply and use it for all items what I have.

3. Then all other items of significant current draw should be connected to voltage regulators connected to the battery in parallel. So have a 5V regulator and a 3.3V regulator, for LCD and motor respectively.

Sounds good. Honestly, I was thinking about that It s possible or not.

I also think about using resistor for decreasing voltage. But I had a prediction that It will warm to resistor.

Again thank you all for your replies. I examined them quickly and there are lot of good information. When I have spare time I will read all of them again slowly.

[jeolex]

Now first step, I will order 12v 2000mA power supply, 5v and 3.3V regülator and then measure voltage and control it with multimeter. If It s ok, from power supply I will make three parallel. One of them directly go arduino power input and the others going 5V and 3.3v regulators. Am I right ?

[Paul__B]

I also think about using resistor for decreasing voltage. But I had a prediction that It will warm to resistor.

Indeed it will.

So what?

You can warm a 2 cent resistor, or you can warm a 50 cent regulator.  Both will heat up to the same degree, because each would dissipate the same amount of power if correctly designed.  Why would you prefer to heat an expensive (well, relatively) regulator and include two extra capacitors instead of heating a cheap resistor if the result is the same?

{Having said that, the regulator would have a capacitor on its input and on its output, and if you use a resistor, you should still have a capacitor across the motor for suppression of interference.}

[Grumpy_Mike]

The very simple answer it to connect the motor, through the transistor to 5V.
Then drive the transistor with a PWM output using an analogWrite command with the PWM value of 168. That will reduce the power sufficiently to prevent the motor burning out.

[jeolex]

Hello again,

I bought 12V 2A power supply and 3.3V regulator for my vibrator motor.

I have a problem with control dc motor with potantiometer. I based on this one;



I have 1N4001 diode, BC547 NPN transistor. So when I connect wires like that motor didn't run. I control all of wires so many time but it didn't work.

My codes are;

Code: [Select]


const int analogPin = A5;
const int motorPin = 9;
int potantValue=0;

void setup(){
Serial.begin(9600);
}

void loop(){
potantValue = analogRead(analogPin);
potantValue = map(potantValue, 0, 1023, 0, 255);
analogWrite(motorPin, potantValue);
delay(200);
}


[JimboZA]

The code says A5, pic shows A0.....

[jeolex]

It's not my sketch. I just based on this one. On my circle It'is connect with A5. I can get potantiometer value, It'is working. I just couldn't control motor with this value. Motor is not run. But when I use middle pin of transistor as a collecter. It's run but so slow and again cant control motor. I was used all combination of transistor

[JimboZA]

Ok well post a drawing of your actual circuit.... Or a photo.

If you're using one of those loooooong breadboards, check that you aren't working (or trying to work) across the two halves when there is often a break in the middle. See pic....

[JimboZA]

Wait a sec.... you're still providing the power to the motor from the Arduino: it might not be able to provide enough current from the 5V pin. I can't be bothered trawling back through this thread to see what the motor current requirement is, but you might consider trying an external power supply for the motor.

edit: schematic of external power added. (I'm loving working with Eagle  )

[jeolex]

I have external power. Not use arduino 5v. My power supply 12v 2A and I use 3.3V regulator for motor.I measure it with multimeter and it s ok 3.3v and I also run motor without transistor.