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1  Using Arduino / General Electronics / Re: Ground loops / High-Low frequencies on: July 27, 2014, 08:32:47 pm
do you think i will need any external driver if I plan to use 3 TLC5940s? These will still control 16 rgb leds.. i am planning on using 15ma i guess for longer life
Driver for what?

You shouldn't need one when used with the TLC5940.

Keep in mind that the way it works is different the 595.  The TLC5940 is a constant current driver.  So you don't need current limiting resistors (other than IREF) and you want to keep the source voltage close to the forward voltage of the LED.  (e.g. don't drive 2V Green LEDs with a 12V battery.)
2  Using Arduino / Installation & Troubleshooting / Re: Arduino Uno external power issues on: July 27, 2014, 08:30:48 pm
Depends on what else is connected.  Arduino board itself draws about 30mA.  That's what those 9V batteries are rated for.  So as long as you aren't powering any sensors, motors, or LEDs off the battery, it should work fine for a few hours (when brand new).
3  Using Arduino / Installation & Troubleshooting / Re: how to identify a arduino? on: July 27, 2014, 07:28:33 pm
Looks like a (Chinese?) copy of an older NG or Diecimila.   Depends on which chip it is using.  Look closer at the markings, if they haven't been sanded off yet.
4  Using Arduino / Installation & Troubleshooting / Re: Arduino Uno external power issues on: July 27, 2014, 07:24:36 pm
First, those batteries are awful.
http://www.baldengineer.com/blog/2014/02/14/9v-batteries-suck/

Second, if you're measuring 4.5v while it is connected, that means the battery is dead (very dead).
5  Using Arduino / Installation & Troubleshooting / Re: Arduino Uno external power issues on: July 27, 2014, 06:55:58 pm
Where are you plugging in the 9V battery?  And what kind is it, the small rectangular type?
6  Using Arduino / Project Guidance / Re: Max Current on Serial Pin TX - Uno on: July 27, 2014, 06:55:10 pm
can the Arduino provide enough current for the LED  on the TX pin while the pin is configured for serial communication?
The driver used is the same regardless.  You can safely source or sink 20mA of current.  Up to 40mA before damage occurs.
7  Using Arduino / General Electronics / Re: Power leaking from fan supply to arduino? on: July 27, 2014, 06:51:41 pm
There are small protection diodes built in the pins, that sometimes allow "back powering" to occur.  However, the fix would be a diode on the signal pin.  That's effectively what you get with a TIP120 already with the diode junction in the BJT.

You could try adding another diode between the pin and base to see if it helps.  The 0.7 voltage drop shouldn't be enough to cause problems turning on the TIP120.
8  Using Arduino / Programming Questions / Re: analong delay? on: July 27, 2014, 09:22:41 am
Set a flag and watch for when millis() goes past 4000ms.  Then run your command.

Something like this (untested) may put you in the right direction.
Code:
bool failFlag = false;
unsigned long failStartTime;

loop() {
if ((FalSafeValue < 100) && (failFlag == false)) {  // need failFlag to be false, otherwise, failStarTime keeps updating
   failFlag = true;  // enable the command
  failStartTime = millis();   // start the clock
}

if ((millis() - failStartTime) > 4000) && (failFlag == true)) {  // see if 4s has gone by yet
   failFlag = false;  //disable the command
   FalSAFE();  // your function
}
}

You could add additional flags and logic to keep running that command for a set period of time as well.
9  Using Arduino / General Electronics / Re: Ground loops / High-Low frequencies on: July 27, 2014, 09:17:20 am
The frequencies you are running at aren't going to be critically affected by a ground plane.  You still want one though.  It provides other benefits: better ground paths for high currents, heat sinking, some minimal decoupling if is connected to power, etc.

Generally I avoid orphans (isolated copper areas).  If I can't connect it to ground (or a power rail) I leave it out. 
10  Using Arduino / Installation & Troubleshooting / Re: Upload stopt at 95% on: July 27, 2014, 09:06:46 am
Instead of a screenshot, select the output text, copy it, and paste it into a post.

Make sure you wrap it with [code][/code] tags.
11  Using Arduino / Installation & Troubleshooting / Re: programmer is not responding arduino uno Mac OS X on: July 27, 2014, 09:04:15 am
have just standard electrical wire for now, along with wire cutters/strippers. will that work?
Depends on what you call "standard electrical wire".  As long as it fits in the holes, there there is nothing special about "jumper wires".
12  Using Arduino / Installation & Troubleshooting / Re: Upload stopt at 95% on: July 25, 2014, 11:15:29 pm
Turn on "Verbose Output" in the Preferences, and try again.
13  Using Arduino / Installation & Troubleshooting / Re: programmer is not responding arduino uno Mac OS X on: July 25, 2014, 11:14:47 pm
Quote
Code:
/dev/tty.usbmodem621
Looks right.

Which Arduino are you using?
14  Using Arduino / Project Guidance / Re: Digital Pin Commands on: July 21, 2014, 09:31:46 pm
One option would be to use a web server example.
15  Using Arduino / Project Guidance / Re: Digital Pin Commands on: July 21, 2014, 07:10:17 pm
How will the Android app communicate with the Arduino?
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