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Topic: Is this an OK setup with an Arduino Pro Mini? (Read 1 time) previous topic - next topic

SquaredPaper

First of all, I want to apologize for the poor way the FTDI-cable is connected to the Arduino Pro Mini in the image shown, but it has to do with that the Arduino Pro Mini in EagleCAD doesn't feature all of it's I/O, that is those who are used for the FTDI connection.

I'm going to explain what I'm doing in order to make it easier to understand just that; the Arduino board is going to read incoming serial commands through the FTDI/USB-connection it has with the computer and translate them into PWM signals to a connected servo, so what I'm achieving that way is a servo controlled by the Arduino which in turn gets the commands from the computer. And what I'm unsure about is if the way I've connected the servo to the Arduino whilst the Arduino itself is connected to my PC. To more specific; is there any chance that the current the servo draws under load will harm the Arduino - or even worse - my computer?

The main reason for my probably unnecessary worry is that the servo has to share the same GND with the Arduino, thus the computers USB port.


jroorda

It looks OK to me.  Just make sure the ground of your 12V supply is tied to the ground for the Arduino.

SquaredPaper


It looks OK to me.  Just make sure the ground of your 12V supply is tied to the ground for the Arduino.


That's exactly how I do it but am I lost or doesn't the current that passes through the servo also enter the Arduino and then the computers USB port? If so, shouldn't there be a limit for how much current it can handle/ground?

jroorda

That all depends on where you hook up the ground from the power supply.  Say if you plug the power supply ground into pin 4 the current will go from pin 23 to pin 4 and back to the power supply.  It will not alter the current flow in the USB cable.  This should be fine as the ground traces on the Arduino are quite substantial.  If I was driving a large load with lots of current I would make sure large wires connected directly from the power supply to both the positive and negative terminals of the servo and then add a small wire to tie the ground from the power supply to that of the Arduino.  It won't carry much current; it just keeps the two supplies from drifting apart. 

The control line for the servo (13) is just a data line and carries a few milliamps at most.

SquaredPaper


That all depends on where you hook up the ground from the power supply.  Say if you plug the power supply ground into pin 4 the current will go from pin 23 to pin 4 and back to the power supply.  It will not alter the current flow in the USB cable.  This should be fine as the ground traces on the Arduino are quite substantial.  If I was driving a large load with lots of current I would make sure large wires connected directly from the power supply to both the positive and negative terminals of the servo and then add a small wire to tie the ground from the power supply to that of the Arduino.  It won't carry much current; it just keeps the two supplies from drifting apart. 

The control line for the servo (13) is just a data line and carries a few milliamps at most.


Sorry for the late reply, but thanks a lot for your input!

One more question though; is it safe to power the Arduino by a 12V RAW input while at the same time use the FTDI cable to communicate with the board? Note that the FTDI also supplies electricity.

jroorda

If the FTDI chip supplies power I would not try to use both that and an external supply at the same time.  It might work if the given Arduino you have is smart enough to switch and only use one supply, but I wouldn't bet on that.  If you have the FTDI connected there is really no reason to power the Arduino from the external supply, as it would simply be redundant. 

SquaredPaper


If the FTDI chip supplies power I would not try to use both that and an external supply at the same time.  It might work if the given Arduino you have is smart enough to switch and only use one supply, but I wouldn't bet on that.  If you have the FTDI connected there is really no reason to power the Arduino from the external supply, as it would simply be redundant. 


Wow, I'm very embarrassed over actually asking that question  :smiley-red: Just realized how stupid it was. Don't even know why I thought that using the RAW input would be useful in my situation. Have to use my "It was because of the lack of sleep"-card on this one. Many thanks for answering it though!

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