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1  Using Arduino / General Electronics / Re: Need help identifying the use for circuit on DC motor on: January 12, 2013, 05:56:44 pm
Thanks alot guys for the quick and informative answers!  smiley-grin
2  Using Arduino / General Electronics / Need help identifying the use for circuit on DC motor on: January 12, 2013, 05:05:22 pm


What's the purpose of those capacitors? What would happen if I would bypass them?
Thanks in advance!
3  Using Arduino / General Electronics / Re: Is this an OK setup with an Arduino Pro Mini? on: September 04, 2012, 06:25:05 pm
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!
4  Using Arduino / General Electronics / Re: Is this an OK setup with an Arduino Pro Mini? on: September 04, 2012, 05:31:14 pm
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.
5  Using Arduino / General Electronics / Re: Is this an OK setup with an Arduino Pro Mini? on: September 01, 2012, 06:02:30 am
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?
6  Using Arduino / General Electronics / Is this an OK setup with an Arduino Pro Mini? on: August 30, 2012, 08:39:43 pm
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.

7  Using Arduino / General Electronics / Current limiting a RGB-LED on: August 26, 2012, 08:12:15 am
Hi guys!

I'm trying to power a RGB-LED from an Arduino Pro Mini (3v3, 8MHz variant) and have got confused over how to connect them up. The reason for my confusion is that 2 of the 3 "colors" have got an forward voltage of 3.2V while the 3rd's is at 2.0V. What confuses me furthermore is that the LED is a common anode-type of RGB-LED so I don't know where and what value of a resistor I should put in series with it. Should I use 2 separate resistors - one for the two colors with the If = 3.2V and one for the single color with the If = 2.0V? But then again the 2 similar colors will draw a total of 0.020+0.020 milliamps through their shared resistor when both are lighted at the same time, right?

Note that I'm going to GND them to 3 digital pins on the Arduino so I can regulate their individual intensity with PWM and power them from the Arduino's Vcc pin (because that's possible, right?).

Thanks in advance!
8  Using Arduino / General Electronics / Re: PWM related servo problem on: May 20, 2012, 07:55:43 pm
You _must_ common the Arduino and servo grounds.  There is no circuit otherwise.

Imagine connecting just one terminal of a battery to some device - nothing is going to happen.

Well I just noticed that there is a potential of ~2V between the servo's power source's GND and the Arduino's GND. Won't the FTDI (thus maybe even the computer's motherboard) take any damage because of this?

Got some images that may better explain what I'm doing:

The setup that fails


The setup that works (with 2 DIFFERENT GNDs)


9  Using Arduino / General Electronics / PWM related servo problem on: May 19, 2012, 07:06:55 pm
Hi all!

First of all; I'm new to the forum and only know that much about electric engineering etc. so please bear with me!

I've recently got myself an Arduino Pro Mini (3.3V @ 8MHz) and tried to hook it up to a servo just to play around with and explore. However, after many hours spent on trying to locate this problem I finally came to the conclusion that my Arduino board simply can not send PWM-signals properly to a servo whilst being powered through a FTDI connector (http://www.sparkfun.com/products/10009). But the strange part is that if I - after have uploading a sketch - disconnect the FTDI connector and power the Arduino board through it's RAW-input with a voltage in the range of 3-12V instead it actually works perfectly. In the first scenario the servo simply position itself to one of it's greatest limits and keeps drawing current there, while in the latter scenario it does exactly what the sketch tells it to do and works normally. Why is this?

The servos 5V-input is connected to an external power source (for obvious reasons) in both occasions. Depending on if the Arduino board itself is powered through the FTDI connector it uses separate GNDs but otherwise it shares the same GND.

I don't think that I have to submit the actual sketch to this post since I'm more than sure that it is not something software related, but if I'm wrong on this then one could find the very same sketch among the Arduino IDE's example sketches on servos - it's called "Sweep".

Thanks in advance!
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