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Topic: PCA9685 power (Read 169 times) previous topic - next topic

MilesMV

Nov 18, 2018, 05:36 am Last Edit: Nov 18, 2018, 06:24 am by MilesMV
So I am working on a project with an Arduino and a PCA9685 by Adifruit and I need some help. So I am using the PCA 9685 to power 16 servos, so it's going to be supplying a good amount of power. Here's where the problem is going to come in; I need to be able to power this off the ground (I'm making something that is gonna fly) and I don't think that rechargeable AA's Adifruit mentioned are gonna cut it. The input port for power is just a + and - port that takes male jumper cables. Adifruit said it could take 4.8v or 6v rechargeable batteries sold by hobbyshops. I did some research and figured out that it's going to be quite difficult to recharge these batteries, forgetting the fact that it could be dangerous(I've had a NiMh cell blow up in my hand before; however, it was just one of the eight). I'm wondering if there is a way to attatch or plug in a port to the PCA9685 that would take power from a 3000+ mAh 4.8v-6v battery that contains standard connectors that would allow me to unplug the battery and plug right into a NiMh charger.

Wawa

I think you have missed the fact that a PCA9685 can't/doesn't POWER anything.
It just provides the control signals for the servos.

Power (the 2-way screw terminal) is NOT connected to the PCA9685 at all,
but goes directly to the power rows of the servos.
On the Adafruit boards through a reverse protection mosfet, no mosfet on the clones.

Only power/signal grounds are shared ofcourse.

The power traces on the Adafruit/clone boards are rather thin. I wouldn't push to much current over them.
You can always connect power (and ground) directly to the servos.
Leo..


TomGeorge

Hi,
Welcome to the forum.


Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html .


Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?


Thanks .. Tom... :)
Everything runs on smoke, let the smoke out, it stops running....

MilesMV

#3
Nov 18, 2018, 06:36 pm Last Edit: Nov 18, 2018, 06:41 pm by MilesMV
Hi,
Welcome to the forum.


Please read the first post in any forum entitled how to use this forum.
http://forum.arduino.cc/index.php/topic,148850.0.html .


Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?


Thanks .. Tom... :)

Hi Tom,
Sorry about that, it was only until later that I realized this discussion was probably in the wrong group. I attached a picture of the hand-drawn drawing. I forgot to mention the fact that it is also going to be controlling 5 ESC's.
Thanks,
Miles

Grumpy_Mike

#4
Nov 18, 2018, 06:51 pm Last Edit: Nov 18, 2018, 06:51 pm by Grumpy_Mike

Let's face it. That is nothing like a schematic is it?

Can you try again please. A schematic shows where every connection goes and you groups of unlabelled boxes just doesn't convey anything to me.

MilesMV

I think you have missed the fact that a PCA9685 can't/doesn't POWER anything.
It just provides the control signals for the servos.

Power (the 2-way screw terminal) is NOT connected to the PCA9685 at all,
but goes directly to the power rows of the servos.
On the Adafruit boards through a reverse protection mosfet, no mosfet on the clones.

Only power/signal grounds are shared ofcourse.

The power traces on the Adafruit/clone boards are rather thin. I wouldn't push to much current over them.
You can always connect power (and ground) directly to the servos.
Leo..


Hi Wawa,
I understand that the PCA9685 only supplies control signals to the servos. From what I understand, the PCA9685's computer processor gets power from the 5v port on the Arduino. So from what you're saying, even if I had a power source, around 5v suggested by Adafruit, connected to the board via the 2-screw terminal, it still would not have enough power running through the small traces on the board to the power the servos. So from what I understand you think I should power the servos separate from the board itself as it cannot supply enough power/current through the small traces on the board to power all of the servos I will have running? Is this correct? Thank you for your response, I found it helpful.
Thanks,
Miles

MilesMV

#6
Nov 18, 2018, 08:13 pm Last Edit: Nov 18, 2018, 08:15 pm by MilesMV

Let's face it. That is nothing like a schematic is it?

Can you try again please. A schematic shows where every connection goes and you groups of unlabelled boxes just doesn't convey anything to me.
Hi Mike,
Sorry about that. I made a new diagram with all connections between every electronic involved. In case it was confusing understanding the servo section of the diagram, I made a diagram with all connections to servos and ESC's from the PCA9685. All servos and ESC's use all 3 ports on the PCA9685. I have attached all of the photos.
Thanks,
Miles

Wawa

Correct. You can power a bunch of small ~500mA hobby servos through the board, but nothing 'bigger'.
Your ESCs could have fatter power/ground wires for motor power, and thinner wires for signal/ground.

Adafruit's boards have a min/max voltage limitation on the power connector because of the reverse voltage protection mosfet. Clone boards don't have that.
Leo..

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