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Topic: One Power Source into Two Power Sources.... (Read 2132 times) previous topic - next topic


I'm driving a servo from an Arduino uno. But I'm using a PWM controller to move the servo. When they share the same 5volt source the PWM stutters. But when I move the Arduino to a secondary the power supply.... Magic!

My main power source is a 5 volt lithium battery. More then enough power to run the servo and the Arduino. So I know that it's not a problem with the Amps getting pulled.

So how can I make my one 5 Volt source split into two different sources?

Thanks a million for any thoughts or ideas!



Apr 19, 2013, 11:47 am Last Edit: Apr 19, 2013, 11:49 am by Erdin Reason: 1
The battery might be strong enough, but there are wires and connections.
I hope you are not using a breadboard ? Those have sometimes bad connection.
The current of the motor could drop the voltage of the Arduino.

Did you connect the 5V battery to Vin, the DC power plug or the 5V pin?
Is that battery 5.0V ? or lower, like 4.5 V ?
The Arduino needs at least 6 or 7V, although 5V should not be a problem.

Was the second power supply also 5V ?
Or did you use a higher voltage at the DC power plug.

I would like to know how everything is connected.
Do you have a large capacitor ? At least 1000uF. Try to add that to the supply voltage of the motor, or the Arduino, or the PWM controller. If think it will make a difference.


[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]


Okay let me backup a little... Maybe I'm asking for the wrong kind of help. I'm a nooby when it comes to the hardware part of things.

I have attached a simple version of my build. I only get the PWM stutter when the Arduino and the servo are sharing the same power. I have no load on the servo motor. My PWM device is following 8 startbits in a loop from the Arduino. I can watch the sync drop out in serial print debug.

Here are the different ways I have hooked up the power to the different devices.

Servo (Arduino USB Power), Arduino (Arduino USB Power), PWM device (Arduino USB Power) - Stutter
Servo (Secondary Power), Arduino (Arduino USB Power), PWM device (Arduino USB Power) - No Stutter
Servo (Secondary Power), Arduino (Arduino USB Power), PWM device (Secondary Power) - No Stutter
Servo (Arduino USB Power), Arduino (Arduino USB Power), PWM device (Secondary Power) -  Stutter

I have the same results as above using a replacing the Arduino Uno with an Atmega328P on a BreadBoard.

My (Secondary Power) supply has been a 7 Volt DSLR Camera Battery, and a MintyBoost kit.(MintyBoost is 5 Volt with a max of 600mA)

Thanks again for the help!


It seems that you have the servo current problem. It's a classic mistake.
Even a small servo could require between 500mA and 1A if it starts moving. That will immediately drop the voltage for the Arduino.

The Arduino can be powered by the USB or with a power supply 7V-12V.

The servo can not be powered by the 5V pin of the Arduino. It should have a power supply of 5V or 6V that is able to provide a peak of 1A.
Running 1A through a breadboard is already a problem.

What is that PWM controller ? Can you post a link to it ?
You use the Servo library that is included in the Arduino IDE ?
That 1000uF for the power supply of the servo I wrote about, that is worth adding.


The PWM Controller is a 5 volt IC with some timed commands. It work fine with or without a pullup resistor.
I'm using the Stock Servo Library from Arduino.
Where would I put the 1000uF inline? On the positive lead to the servo?

Thanks for the help Erdin!


The 1000uF at the power supply wires for the servo, that is the 5V and GND on the breadboard.
But you still have to use a seperate 5V or 6V power supply for the servo.

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