Question on power supply and USB port?

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nataku
 
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Question on power supply and USB port?

Post by nataku »

Hi,
Does anyone know if it will be alright to connect the Uno to the computer and at the same time have a 9V battery connected for example connected to the DC inputs?

And second question.
I tried measuring the output amps of the 5V pin through a motor and it is larger around 290mA and yet the motor does not turn when the board is powered from USB port. I have to switch it to a 9V battery supply for example for the dc motor to run buy yet when I measure the current draw it is only 220mA.
This is just a cheap DC Toy motor. And is it even possible to have the motor see that 290mA and not even run?

Thanks for the help.

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adafruit_support_bill
 
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Re: Question on power supply and USB port?

Post by adafruit_support_bill »

The Uno has a circuit to switch between power sources automatically. So you can have both the 9v and the USB connected at the same time.

For you second question, it would help to tell us more about your system. How are you driving the motor (motor shield, transistors, H-bridge etc)?
Do you have any specifications for the motor (voltage, current ratings etc)?

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nataku
 
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Re: Question on power supply and USB port?

Post by nataku »

Thanks Support_Bill,

The motor spec is attached. I think I should have bought the 70mA no load current version. This one has a 320mA no load current.

I tried driving it 2 different ways. One from the Arduino 5V supply and another time is from a separate external supply (like a 2x1.5V AA alkaline battery).
It seems that only when I change the speed instantaneously from 0 to 255 in the program, then it would work. Otherwise, it was very iffy.
Furthermore, I am guessing when I insert my DMM to measure the currents, it adds burden to the circuit so I am seeing less than what the motor is actually drawing.

Anyway, I am attaching also the circuit I am using.

My conclusion was I should try a using something like a motor shield or an h bridge or even as simple as providing an external supply that can provide may be like 1000mA. I do have the transistor collector current that may limit what can be drawing by the motor.

Please let me know if I am off base.
Attachments
Screenshot_4_14_13_3_43_PM.png
Screenshot_4_14_13_3_43_PM.png (21.15 KiB) Viewed 315 times
hobbymotor.jpg
hobbymotor.jpg (262.32 KiB) Viewed 315 times

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adafruit_support_bill
 
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Re: Question on power supply and USB port?

Post by adafruit_support_bill »

It seems that only when I change the speed instantaneously from 0 to 255 in the program, then it would work. Otherwise, it was very iffy.
This is a common problem with low-voltage motors. They are hard to start and very difficult to control at low speeds. One trick that works sometimes is to give it maximum throttle (255) just long enough to get it turning, then throttle back to a slower speed. But in general, you should have better luck with a motor designed for higher voltages. http://www.adafruit.com/products/711

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nataku
 
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Re: Question on power supply and USB port?

Post by nataku »

Thanks.

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