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1996  Using Arduino / General Electronics / Re: Share ground pin with six PWM wires on one UNO? on: November 06, 2013, 07:28:23 am
I have six channels of LED stipes. Can I share the ground pin with all six channels?
UNO has six PWM pins but it has one ground pin.
Can I wire all six ground wires (+0V) together and then connect it to the ground pin on UNO?

You don't have a choice, you MUST do that or you risk destroying the arduino + strips + everything else in the area.

I assume you have an external power supply for so many LEDs so you should connect Arduino ground to the ground on the power supply along with the ground from the LED strips.

Because it's so critical, I wouldn't just poke a wire into the Arduino edge connector, I've killed Arduinos by a ground wire falling out. These days I solder a wire to top of the Arduino USB socket then connect it to a screw terminal on the power supply.

I'm not kidding, here's a picture of one of my Arduinos that's been in a device which was used to drive LED strips. You can see the solder blob on the USB connector where the wire was.
1997  Using Arduino / General Electronics / Re: powered usb hubs ... on: November 06, 2013, 07:17:37 am
If it's a powered hub you have to assume they already thought of that and put something inside the hub to make sure it works....

1998  Using Arduino / General Electronics / Re: What is the reason you find 100nF || 47uF in circuits? on: November 06, 2013, 07:16:15 am
in a parallel wiring of capacitors. But why would someone do this with 100n || 47u?
47.1u or 47u? I'd think that this is not much difference and let the 100n be.

It's not about capacity, it's about response time. A small ceramic will respond very quickly giving the slower electrolytic time to respond with its larger capacity.
1999  Using Arduino / General Electronics / Re: Uber cheap 40 pin ZIF sockets on ebay... on: November 06, 2013, 07:14:38 am
I've used them, no problem...
2000  Using Arduino / General Electronics / Re: power adapter on: November 05, 2013, 11:07:34 am
hahaha, okay thanks for that. not sure i grasp exactly what you mean (in particular how would the thing stop at 5v and not drop further?).

5V is approximate and only when it's connected to the device it was designed for.

It will drop further than 5V under heavier loads.
2001  Using Arduino / General Electronics / Re: power adapter on: November 05, 2013, 10:08:33 am
I've found a nice 5v ac/dc power adapter which i want to use to power up my arduino. now the thing is when i measure V instead of 5 i get 8.~ which may be okay i guess. what bothers me however is that symbol on the output side:

As others have said, that's just the symbol for "DC power"

What bothers me is that is says 5V but you measured 8V. That means the supply is unregulated. It's designed to drop down to approximately 5V when you apply a certain amount of load to it (and we don't know what that load is...)

If you connect it to the Arduino external power socket it might drop down too low for the voltage regulator to work and the Arduino won't get a full 5V.

If you connect it directly to the Arduino 5V pin it might supply more than 5V and hurt the Arduino.

In other words: It's bad news. I wouldn't use it with an Arduino if I were you.
2002  Using Arduino / General Electronics / Re: Understanding forward current on: November 05, 2013, 09:29:56 am
This isn't the real story.

It was the short version  smiley

2003  Using Arduino / General Electronics / Re: Understanding forward current on: November 05, 2013, 08:43:32 am
LEDs work by controlling the current, not the voltage.

The reason is their resistance varies wildly as you approach the sweet spot (usually 20mA). Trying to pick a resistor isn't easy. You can get big variance in brightness between LEDs.

This is why you see special chips just to control LEDs.

Quote
I need to stick a bunch of these LEDs behind a BC547 NPN Transistor

For switching large numbers of LEDs I like to use an6884 chips (or ka2284 which work identically). Yes, they're "VU meter" chips but if you put the input pin HIGH all the LEDs switch on.

Think of them as a BC547 with five input legs, each with proper current regulation (no resistor needed!) Just connect the Arduino output pin to pin 7 of the chip. You can connect dozens of them to a single Arduino pin.


2004  Using Arduino / Microcontrollers / Re: what's i'm receiving? on: November 05, 2013, 07:51:21 am
If i send 256:
Code:
python i2c.py 256
i get 0, here is the problem, i think i have declared a variable bad. Can you help to locate it?

I suspect you're sending bytes.

256 doesn't fit in a byte, it will turn into a 0.

2005  Using Arduino / Microcontrollers / Re: attiny84 baudrate problem on: November 05, 2013, 05:40:36 am
not entirly, but when im trying to compile my code with the
Serial.begin(31250);
i get this error:
Code:
In member function 'void TinyDebugSerial::begin(long int)',
    inlined from 'void setup()' at basis.ino:44:
C:\Program Files (x86)\Arduino\hardware\tiny\cores\tiny/TinyDebugSerial.h:694: error: call to 'TinyDebugSerialBadBaud' declared with attribute error: Serial (TinyDebugSerial) supports three baud rates: 9600, 38400, or 115200
.

Ok, I didn't know "supporting libs" meant "TinyDebugSerial".

Looks like you're going to have to go in and hack the source code for TinyDebugSerial to support another baud rate.
2006  Using Arduino / LEDs and Multiplexing / Re: Best approach for addressing 64ish bright LEDs on: November 05, 2013, 05:31:07 am
Here are my questions:
1.  Does a Digital LED strip and an Addressable LED strip mean the same thing?  Adafruit calls them Digital, but stores on Alibaba/ DH Gate etc call them Addressable.  Also I don't care about PWM, I just need to turn them on and off.

I think so.

2.  Does anyone know of a good product that is an array of addressable LED pixels or strip that are just ultra bright white and not RGB?

Addressable but not RGB? I've never seen one.

You can get WS2811 chips on little PCBs: http://www.ebay.com/sch/i.html?_nkw=ws2811+circuit+board

That's the same chip as in the LED strips (so the same drivers will work) but you can connect 3 white LEDs. If you use those the wiring will be much neater/simpler than using shift registers.

When you're working with 20mA LEDs brightness is usually solved by adding more LEDs. If you want high power LEDs (eg. 1W) you can still use the WS2811 boards but you need to add a transistor and some resistors for each LED.

3.  Does anyone have any link/advice about driving 64+ ultra bright LEDs from a battery?  I want to keep this thing portable but obviously I still need to cart around some batteries.

Reading between the lines: I'm guessing you're not going to light them all up at the same time. If you're only lighting a few of the LEDs at once then batteries aren't a problem.

2007  Using Arduino / Microcontrollers / Re: attiny84 baudrate problem on: November 05, 2013, 05:14:18 am
but the supporting libs only allow me to program the  in 9,6k, 38,4k and  115,2k baudrate.

Are you sure? Last time I looked they supported *any* baud rate.

2008  Using Arduino / LEDs and Multiplexing / Re: 10x led matrix with 7219 for clock on: November 05, 2013, 05:05:05 am
I just want to point out that when I said "100% the way to go" it was for physically rotating the matrices, not the software approach.
2009  Using Arduino / Microcontrollers / Re: Arduino Pro Mini 3.3V HC-06 Bluetooth Module on: November 05, 2013, 05:01:58 am
Do you have the bluetooth module connected when you try to upload?

Bluetooth connects to the serial pins and that causes conflicts - the program is uploaded over those pins.

For development it's easier to connect the Bluetooth module to some other pins and use SoftSerial.
2010  Using Arduino / LEDs and Multiplexing / Re: 10x led matrix with 7219 for clock on: November 05, 2013, 03:39:45 am
Drawing text at an arbitrary horizontal position needs a lot of bit shifting and twiddling. It's basically a monochrome sprite routine.

it depends on what the original poster feels most comfortable with.

You and me could code it in our sleep ... but the OP obviously isn't so comfortable with bit shifting.
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