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1996  Using Arduino / LEDs and Multiplexing / Re: Experience with 74hc595 on: November 18, 2013, 07:17:23 am
They can obviously take some abuse - the evidence is all around us.

There's another limiting factor which is that the voltage output drops with increasing current.

Look at VOH in the datasheet. With 6V Vcc and 7.8mA draw, the voltage drops to 5.2V.

It doesn't specify values for higher currents than 7.8mA but with Vcc=5V and 20mA draw it will probably drop down below 3V.

At 3V a Blue LED won't allow 20mA to pass. If you connect a blue LED to a pin you'll never reach 20mA because there won't be enough volts to push that much current through the LED. It will reach equilibrium at a value less than 20mA.

The same sort of thing might happen to the whole chip, that's why they survive. As an experiment you could set it up to draw 20mA on each pin then turn the pins on one at a time and measure the current going into the chip (and on each pin). Draw a graph of the result and post it.

Just because the chip survives doesn't mean it's good engineering. The LEDs will get dimmer, the chip could heat up...it might even damage it in the long term.

1997  Using Arduino / LEDs and Multiplexing / Re: Experience with 74hc595 on: November 18, 2013, 05:51:30 am
Yep. There's no confusion over it or "different answers". The specification says 70mA per chip.

Per pin, in what I linked.

The pins you're referring to are "Vcc" and "GND", not I/O pins.

I'm not sure how you could get more than 70mA per chip without overloading one of those.

1998  Using Arduino / General Electronics / Re: Need help I've somehow blew up my arduino on: November 18, 2013, 05:44:59 am
Just checked online and the processor can operate between -40 and +85oC so I don't know if 50oC after a minute is bad or not?

Just because the chip can take it doesn't make it OK.

Something is wrong. Arduino chips don't normally heat up.

1999  Using Arduino / General Electronics / Re: Need help I've somehow blew up my arduino on: November 18, 2013, 04:28:29 am
Quote
You got the polarity backwards on the barrel connector.
I thought it was protected internally from that?

It could also be that the positive pole made connection before GND when you plugged it in. That's almost guaranteed to kill it.

Moral: Ground connections are important when you have multiple power sources. Always connect GND before any other wires.


2000  Using Arduino / LEDs and Multiplexing / Re: Multiple leds, independent. on: November 18, 2013, 04:09:46 am
My page which MichaelMeissner has very kindly linked to avoids talking about state machines, and keeps it simple.

Short URL: http://www.gammon.com.au/blink


That's a good way to think about it...
2001  Using Arduino / LEDs and Multiplexing / Re: Multiple leds, independent. on: November 18, 2013, 04:08:53 am
You may be right. My view is if you're new to programming, you are SOOOOO not ready to hear about state machines, especially if they may not be necessary for the task.

Teaching them about "delay()" doesn't help.

"delay()" is the devil's function.
2002  Using Arduino / LEDs and Multiplexing / Re: Experience with 74hc595 on: November 18, 2013, 04:00:11 am
I was looking around the net and there is awful lot of different answers, how much current are the chips actually able to provide.

Not much.

The datasheet clearly says max. 35mA/pin, max 70mA through Vcc or Vss and power dissipation of 500mW

Yep. There's no confusion over it or "different answers". The specification says 70mA per chip.

I see a lot of projects around, that are exceeding these limits.

There's also millions of LEDs attached to Arduino pins without resistors, that doesn't make it right. Most of those people have never read a datasheet in their lives.

For sinking current, use a TLC5916 or TLC5940. They're current controlled and the difference in price is made up for by not having to mess around with resistors, etc. (IMHO)

For sourcing there's the TPIC6B595, but it's usually better to sink.
2003  Using Arduino / Microcontrollers / Re: Usin Pro Micro as ISP on: November 17, 2013, 12:39:25 pm
slave reset - 10 (uno) - seems to be D17  on Pro Micro  - but there is no D17 on the board?

Pick a different one. I'm sure the sketch lets you choose different pins.
2004  Using Arduino / LEDs and Multiplexing / Re: Problem arduino Duemilanove and TLC5940 on: November 17, 2013, 11:20:08 am
but how can i solve this problem?

I don't know, I can't see what you're doing.

There should be a zero Ohm from the TLC GND pin to the Arduino GND. Find out why there isn't.
2005  Using Arduino / LEDs and Multiplexing / Re: Problem arduino Duemilanove and TLC5940 on: November 17, 2013, 10:17:34 am
OK,  there's the problem!

Both 5V and GND pins should have zero resistance between Arduino and TLC.

2006  Using Arduino / LEDs and Multiplexing / Re: Problem arduino Duemilanove and TLC5940 on: November 17, 2013, 09:32:24 am
i Try to measure the resistance between GND of TLC and usb case of arduino and it is similar than the resistance between the TLC 5V and arduino 5V

Is it zero?
2007  Using Arduino / General Electronics / Re: How to solder these modules? on: November 17, 2013, 07:16:53 am
They're designed to be mounted on little PCBs.

They obviously can't be plugged into breadboards without some sort of adapter (or some wires...solid telephone wire works well on breadboards and would solder easily to that module)
2008  Using Arduino / LEDs and Multiplexing / Re: Problem arduino Duemilanove and TLC5940 on: November 17, 2013, 07:14:18 am
It's probably some sort of wiring problem, but I can't see your breadboard from here.

Check your GND connections carefully, make sure there's connection to GND on the Arduino. Don't trust wires/breadboards, measure resistance from the GND pin on the TLC to the USB connector case on the Arduino.

Similarly the +5V - measure from the TLC pin to a separate wire in one of the Arduino 5V connections.
2009  Using Arduino / Microcontrollers / Re: [SOLVED] Have I broken it? - uploading using Arduino ISP on: November 17, 2013, 05:55:00 am
Out of curiosity, I wonder why the IDE got it wrong?
Especially as it had no problem uploading sketches to an Attiny. Is it possible there is something in the Attiny files that tells it what baud rate to use? Where would I look?

Baud rates are in the file "boards.txt"
2010  Using Arduino / Microcontrollers / Re: Mesureing square wave without using pulse in or a blocking function? on: November 17, 2013, 05:54:04 am
The details of the measurement hardware are in the datasheet, look for "Input Capture Unit" in the section on Timer1.

Maybe there's another library out there which has more range. Google for them, eg http://interface.khm.de/index.php/lab/experiments/frequency-measurement-library/


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