Show Posts
Pages: 1 2 3 [4] 5 6 ... 91
46  Community / Products and Services / Re: The Zero is upon us! on: May 18, 2014, 06:17:00 am
Atmel interviews Massimo Banzi about the ZERO:
https://www.youtube.com/watch?v=6st9ym0a6Sk
47  Using Arduino / LEDs and Multiplexing / Re: Neopixels - Is it possible to do anything in the middle of an update? on: May 16, 2014, 09:38:13 pm
Ha, I just noticed all those articles on Neopixels were just posted over the last few days.  Lucky me. smiley
48  Using Arduino / LEDs and Multiplexing / Re: Neopixels - Is it possible to do anything in the middle of an update? on: May 16, 2014, 09:28:43 pm
Hm, it seems that page does have the answer:

Quote
Q: I have some interrupt timing sensitive code that I have always wanted to run while also driving NeoPixels. Are you saying this might be possible?
A: No problem! As long as you can keep your interrupt service shorter than ~5us, you can leave interrupts on almost all the time while driving your NeoPixels. The only place where you need to turn them off is during the very brief moment when sending a 0-bit pulse to make sure that it stays below the maximum T0H length. If you add the following code to protect the sending of the 0-bit in sendBit() …

I'm not certain that my audio interrupt is less than 5us, but I did calculate there's 45us between samples, so... maybe it will work?
49  Using Arduino / LEDs and Multiplexing / Re: Neopixels - Is it possible to do anything in the middle of an update? on: May 16, 2014, 09:17:16 pm
Hm, I found this interesting page:
http://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/

I'm still reading through it, but it may hold the key...
50  Using Arduino / LEDs and Multiplexing / Neopixels - Is it possible to do anything in the middle of an update? on: May 16, 2014, 09:06:08 pm
I have a board where I'm playing audio at 22khz and I'd like to also update a short string of Neopixels (less than 10).  I've only got 45 microseconds between each sample, and I have to transmit 16 bits to my DAC every time, so I may not even have the 30 microseconds between each sample required to send one full pixel's worth of data.

I was looking at Adafruit's tutorial here:
https://learn.adafruit.com/adafruit-neopixel-uberguide/advanced-coding

And clearly, I can't hold the line low at any point for longer than 50us or the data will latch into the pixels. and the next bit of data I send will go to the first pixel. 

However, I'm wondering if perhaps I could hold the line high longer than usual, and what will happen if I do.   

For example, is the pixel keying off the length of the low signal after the high signal to decide if a bit is 0 or 1, or is it keying off the length of the high time, and the length of the low after that doesn't matter as long as it's not so long (50us) that it causes the pixel to latch the data?  Does it only decide what bit was sent after the low signal goes high again?  It seems like it would because otherwise it might load a new bit when the intention was to latch the pixel.  I guess I should look at the Arduino lib and see what they do at the end of the data transfer... either they take the signal high like the datasheet shows at the end, then go low for 50ms, or they'd just hold it low after the last bit was transmitted, which would probably mean the high time is how it decides what bit it was.

51  Community / Gigs and Collaborations / Re: Need a freelancer to help build an array of LED strobes on: May 16, 2014, 09:35:11 am
If it's a paid commission, I'm definitely interested.  I'm located in southern New Hampshire. 

I have some experience with strobes:
https://www.youtube.com/watch?v=iQdRjXtXgdg

At 1:45 you can see a 3W led strobe fire off.  Whether that would be bright enough for you with 24 of them going off at once, I'm not sure, but the video doesn't really do it justice, and it wouldn't be a problem to use higher wattage LEDs if necessary.

My email address is scswift@gmail.com, feel free to get in touch.
52  Community / Products and Services / Re: The Zero is upon us! on: May 16, 2014, 05:16:38 am
I don't like the inclusion of a second chip for debugging which won't be available for use in our own designs, and while I understand why Atmel would want to promote their new chip, and like the small package, I'm disappointed that they've announced this before the chips are even available. 

I use the Arduino for commercial ventures, and if the necessary chips to replicate it within my own designs aren't in stock anywhere in significant quantities, then this board is useless to me. 
53  General Category / General Discussion / Arduino Zero on: May 15, 2014, 09:04:33 am
So I just had this pop up in my Facebook news feed:
http://atmelcorporation.wordpress.com/2014/05/15/arduino-and-atmel-debut-zero-dev-board%E2%80%A8%E2%80%A8/

Cool!  I thought... A new 32 bit Arduino to base my own board designs around.  And the processor on it is nice and small, unlike the Due's enormous 144 pin beast.  Hm, I wonder what that QFN package next to it is?

Then I checked Digikey for stock on the chip.  BUZZKILL!   ZIP. NADA. NOTHING.

Oemstrade?  Again, ZILCH.

Hm, looks like the ZERO is living up to it's name already.  There's ZERO chips in stock anywhere!

Okay well that's disappointing...  Well maybe we could use the D20 instead?  Hm... they're compatible, and lots of those in stock... but, oh dear, those don't support USB.  The D11 then?  Those support USB and are also compatible, I wonder what they're missing... hm, before I waste my time figuring that out better check the stock...  oh for Pete's sake!  There's none of those in stock anywhere either! 

Why in the hell would they release a new Arduino based on a chip which isn't available anywhere?  I mean I get why Atmel would want to release one to promote their new chip, but this has the official Arduino seal on it and everything.  Why do we get this instead of something based on the Xmega which is widely available?  I know some have done most of the work porting the IDE to that, so it seems like a logical step to take.  I mean it's 8 bit, but it's 32mhz and at least you can get the chips. :/

Oh well, maybe in a year this will be a viable option for real products.  I doubt Atmel is gonna flood the market with tens of thousands of these chips in the next few months when Digikey doesn't even have a listing for them.
54  Using Arduino / General Electronics / Re: How many watts will this amplifier need to dissipate? on: May 07, 2014, 10:55:15 am
I found this document on Class D amplifier design:
http://www.irf.com/technical-info/appnotes/an-1071.pdf

On page 6, on the right side, it shows the equations for calculating power losses in a class D amp.

It looks like in addition to the switching losses, (which I think are constant, but I can't say for sure because I don't know what some of those variables represent) there are also the conduction losses that MarkT mentioned, which are given by:
(Rds(on) / Rload) * Pout

And, there are gate drive losses for the mosfets, which appear to also be constant so can just be considered switching losses.


Anyway, given that chart in the datasheet indicates a large drop in dissipated power as the output power is reduced, I think it's safe to say that the conduction losses are the biggest contributor here to the dissipated power, and as those do vary with the volume, a class D amp will in fact draw less current and dissipate less heat when you turn the volume down or the music is quiet.
55  Using Arduino / General Electronics / Re: How many watts will this amplifier need to dissipate? on: May 06, 2014, 01:32:48 pm
I'm guessing it's something to do with where it says "...with an inductor in series..." at the top of the page.

I dunno, that sounds to me like they were just simulating a speaker with a resistor and inductor.
56  Using Arduino / General Electronics / Re: How many watts will this amplifier need to dissipate? on: May 06, 2014, 01:30:30 pm
Here class D losses are I^2.R in the MOSFETs

What do you mean by I^2.R?  I^2 is obviously current squared, and R is resistance, but what's with the dot?
57  Using Arduino / General Electronics / Re: How many watts will this amplifier need to dissipate? on: May 06, 2014, 10:45:04 am
Also remember most audio signals are nowhere near maximum amplitude most of
the time, its only the percussive peaks that get up there, so in practice the dissipation
will be a lot less than the maximum.

Not in a class D amplifier.

While I'm inclined to agree with you because what you said earlier seems to make sense, if that's true, then how do you explain the efficiency vs output power graph in the top center of page 8 in the datasheet:
http://datasheets.maximintegrated.com/en/ds/MAX9744.pdf

That graph is for a 12V input into a 4 ohm load.  The line at the bottom shows the power dissipated vs the output power.  The power dissipated clearly increases in a linear manner with the output power, which varies with an increasing duty cycle.

It's not even a little change either, it's a big change in power dissipation.  And that directly contradicts your suggestion that the dissipation remains constant.
58  Using Arduino / General Electronics / Re: How many watts will this amplifier need to dissipate? on: May 05, 2014, 02:09:52 pm
You mean the power dissipation, not the output power, don't you?
59  Using Arduino / General Electronics / Re: How many watts will this amplifier need to dissipate? on: May 05, 2014, 12:18:36 pm
A theoretically ideal Class D amplifier is 100% efficient and doesn't dissipate any heat.    Page 15 of the datasheet shows that it's more than 80% efficient across most of the output range, so at 20W output, you'd be dissipating about 1W. 

20% of 20W is 4W.  Where are you getting 1W of power dissipation?

Also on page 8 of the datsheet, the second chart at the top shows that at 12V, with a 4 ohm load, the PD is 5W.  I'm still unsure if that is for both channels at once or for each individual one.


Quote
Normal music & voice has a peak-to-average power ratio of around 10, so with 20W (undistorted) peak output, the average output would be about 2W.

Well, that's good to know, if true.  That implies that at 16W output for the 12V into 4 ohm case, at 85% efficiency, you've got 1.6W of average power * 0.15 percent losses = 0.24W of power dissipation.

But what the other fellow said about the power losses being tied to the switching of the mosfet and nothing else seems to make sense, and even if the average power output were only 2W, the dissipated power would remain the same because all you're varying is the duty cycle to get that lower power output while the PWM frequency, and thus the number of times per second the mosfets switch and pass through that high resistance state, would remain the same.
60  Using Arduino / General Electronics / Re: How many watts will this amplifier need to dissipate? on: May 05, 2014, 11:45:03 am
That's... counter-intuitive.  At first I thought you must be wrong, because the duty cycle has to vary to vary the power into the speaker, but it doesn't really matter what the duty cycle is, does it?  As long as it's greater than 0, if the PWM freqeuncy is 300KHz, which it is for this chip, then the mosfet will transition from high to low 300K time a second, regardless of whether the duty cycle is 5% or 95%.  All that varies is how long in that period it is in the on or off state.

Interesting.

That raises more questions than it answers though, in regards to heat dissipation.  That would mean that at 12V into a 4 ohm load, regardless of how loud the music is, I'm going to dissipate 5W.  But that seems to be more than... 

Wait...
θJA, Single-Layer Board................................................37°C/W

That's JA, not JC.  That's the temperature rise if the chip is only dissipating power through the air surrounding it.

It must be able to dissipate much more heat directly through the heat sink into the PCB.  But where's the JC rating?  And why does that rating specify that it is for a single layer board, if it's the rating for dissipation to ambient air?  And why is there another rating for JA for a multi layer board?   None of this makes any sense.
Pages: 1 2 3 [4] 5 6 ... 91