Is this the correct way to power a servo & board using external power source?

Hi all,

I was wondering if my schematic below is correct when it comes to using a single external power source to power both an Arduino board and servo. If so, can I just continue to add more servos in parallel with no problem?

This is my very first project with Arduino. I'm was hoping someone could confirm that I have applied my research correctly when designing this circuit, before I hook it up and blow everything! :wink:

I've left off the a bunch of LED's and buttons from the breadboard as I figure they are probably irrelevant to my question.

EDIT: I've updated my schematic to the second image.

Original

Revised

Thanks in advance for your help!

If you connect your circuit like that you will fry your servo in 50mS !
Servos cannot be powered by a voltage greater than 6V. Just plug the servo red wire into the arduino +5V.
The arduino can handle one servo no problem.

Thanks Raschmmel. How would I work out how many servo's I can add straight to the board before needing to operate them from a separate power supply?

The servo I am getting delivered has the following specs:

  • Power Supply: 3 to 7.2 V
  • Current: 8mA (rest) - 350mA (empty)
  • Amplitude: rotation continue
  • Torque @ 4.8 V: 11kg/cm
  • Torque @ 6,0V: 13kg/cm

Thanks for your help!

When I said you could power a servo from the arduino +5V I SHOULD have qualified that by saying you can power an UNLOADED
servo (WITH NOTHING CONNECTED TO THE SERVO ARM), for testing code. When powering LOADED servos that are actually driving a load, you need to use an external 6V battery pack consisting of 4 AA batteries.

Ah okay. Well this servo will be pulling a load of about 3kgs. As you mentioned, I need to hook up to an external power source. Is the wiring in my diagram suitable (provided I change from a 9V battery to a 6V setup)?

Yes. but I don't know what kind of servo you have that can lift almost 7 lbs. I think that even if you replaced the AA batteries with D cells, it still might not supply enough power. What servo are you using ?

6V is not enough to power the Arduino through the power jack (or Vin). You can connect the 6V to the servo and to the Arduino 5V input through 1 or 2 diodes (1N400x) to drop the voltage to below the maximum Vcc for the mega328 of 5.5V.

You can connect the 6V to the servo and to the Arduino 5V input through 1 or 2 diodes (1N400x) to drop the voltage to below the maximum Vcc for the mega328 of 5.5V.

6V-0.7V-0.7V=4.6V (forward voltage drop of 1n400X is 0.7V)

Thanks for the responses! I've had another look at the circuit after reading what you guys have said.

Is this more suitable? My Arduino board says "7-12V DC recommended" for input voltage.

In the diagram below, this is the 12V to v6 3A Buck step down module.

And the servo(s) I propose to use is/are this Towerpro MG995

That should work but if you want to know the correct way to represent electronic wiring diagrams, the buck converter should be shown as a box with power AND GND as an input and 6V AND GND as an output. Obviously you know the buck converter won't work without the ground connected and the servo won't work without the ground from the buck converter so GND should come in the left side of the buck converter and exit the right side to be correct.

raschemmel:
That should work but if you want to know the correct way to represent electronic wiring diagrams, the buck converter should be shown as a box with power AND GND as an input and 6V AND GND as an output. Obviously you know the buck converter won't work without the ground connected and the servo won't work without the ground from the buck converter so GND should come in the left side of the buck converter and exit the right side to be correct.

Ah, yup. Totally missed that. Updated to reflect. Also, thanks again for your help.

I see that in the diagram you showed you connected the servo pins to 2 and 3. Pin 3 is marked with PWM capabilities, but not pin 2. I would recommend using only PWM pins for servos for better accuracy.

TheTrollingHACKER:
I see that in the diagram you showed you connected the servo pins to 2 and 3. Pin 3 is marked with PWM capabilities, but not pin 2. I would recommend using only PWM pins for servos for better accuracy.

When using the standard Servo library servos are not controlled with hardware PWM so there is no value in using PWM pins for them. Any digital pin works equally well.

Steve