Show Posts
Pages: [1] 2 3 4
1  Using Arduino / LEDs and Multiplexing / Re: Noob question on LEDs and amps draw on: April 16, 2013, 04:12:10 pm
As for it only drawing 400ma with .... I'd probably not go any higher!   

That line you wrote got me thinking twice about it. The median forward voltages specified for each die are approx, 2.5 + 7.6 + 3.8 = 13,9v * 0.7a = 9.73watts.

So - doh - of course I'm not meant to run _each_ led at 700ma.

Thanks for your input, which helped me wrap my head around it.
2  Using Arduino / LEDs and Multiplexing / Re: Noob question on LEDs and amps draw on: April 16, 2013, 03:39:57 pm
if you were extremely careful and can dial in the voltage (any jumps in voltage would cause it to max out and kill it very quickly, so unless you can do this, don't)  slowly increase until you see a 700ma.. draw, then have a look at the voltage...

Hi again cjdelphi,

well I slowly cranked it up until I drew 700ma - at which point the voltage read 4.2v. That's in the extreme above the 2.95v that's specified as max in the data sheet.

I'm quite curious about it. The thing got hot, of course, but not more than I'd expect from a 10w RGB LED, not something that proper heatsinking wouldn't take good care of.

Anything comes to mind?
3  Using Arduino / LEDs and Multiplexing / Re: My RGB LED Stairs Illumination video on: April 16, 2013, 05:59:19 am
Here is a photo of the breadboard design:

That's the most colorful breadboard design I've ever seen :-) Beautiful. I bet it's going to make you feel heavy-hearted when you have to pull it apart ;-)
4  Using Arduino / LEDs and Multiplexing / Re: Noob question on LEDs and amps draw on: April 16, 2013, 05:57:33 am
As for it only drawing 400ma with .... I'd probably not go any higher!   

I should add that at 400ma it's ever so bright as I'd ever imagined it would be, so I'm certainly not disappointed by the unit - just trying to see how high it will go.
5  Using Arduino / LEDs and Multiplexing / Re: Noob question on LEDs and amps draw on: April 16, 2013, 05:55:41 am
1. at 2.96v, if you could find a data sheet on one of these led's you'd probably find a graph which shows the voltage / current draw, higher the voltage the current, know it up to 3.2v or higher and you'll reach
your magical figure....
2. let's suppose you were right, 2.96v is the correct forward voltage, that would imply your power supply is not able to deliver anything 400ma.... (I highly doubt it though)  get your multimeter out and increase it to 3v, you should see around 500-600ma draw....

Thanks a lot for your input,

that's the thing, the data sheet seems to imply the red led should be well able to take on the 700ma the thing is speced for (attached image) :-? At 2.95v I should be getting 1000ma out of it (which is the hightest rating in the datasheet - I haven't dared go above 3v, but I'm sure the amerage draw would increase if I did). Am I reading the data sheet wrong?
6  Using Arduino / LEDs and Multiplexing / Noob question on LEDs and amps draw on: April 16, 2013, 05:38:53 am
Hello all,

and please bear with me, it's pretty basic,

I am wanting to experiment with high-power red-green-blue LEDs and have myself a LZ4-20MC00 (http://dk.mouser.com/Search/ProductDetail.aspx?R=LZ4-20MC00virtualkey62410000virtualkey897-LZ420MC00) for that purpose. First off I'm putting a regulated power-supply to the individual leds, just to see the effect of them. So I consult the datasheet and dial the 1.5a regulated power-supply in to match the specified max forward voltage - for the red color that's 2.96v, for example.

The thing is, the LEDs is rated 700ma for each individual LED. But at max specified voltage, with no resistor to keep anything down, I'm only getting about 400ma through my multimeter - how come? The datasheet doesn't state alternative ma's for each of the 4 leds inside the lens, and surely my power supply will happily offer all the led is willing to take on.

Thanks for helping out.

7  Using Arduino / General Electronics / Re: Mosfet, switching external power - wire to ground? on: April 14, 2013, 05:16:15 am
In the hope it may help others, here's the PCB (attached, login to see it) of the schematic.
8  Using Arduino / General Electronics / Re: Astable triggering monostable on: April 14, 2013, 04:59:22 am
Why don't you just build an astable version with a very low duty cycle? 2 seconds high, 120 seconds low, that's a duty cycle of 1/60. You will need only one ne555.

Hello muddy,

thanks for your feedback. I'm just starting out in electronics, so that's the main reason why there's two 555's - I hadn't the tenacity to come up with a one 555 solution. Could you offer the schematic for the solution you describe above? Thanks in advance.
9  Using Arduino / Microcontrollers / Re: Got wrong pitch FQFP MCU - possible to make a save? on: April 10, 2013, 02:52:09 pm
Sure.  The way I have done it is actually I pre-tin the pads with regular solder and lots of flux.  I reflux the whole footprint and the IC and I melt the solder all at once with the hot air and place the QFN on top of that, it usually settles right in.  It will never settle between  the pads which is great but it can settle off a whole pad so have tweezers ready to give it a nudge if it does that.  The microscope is to check out if everything went OK and how all the heels look which is impossible to see with no or low magnification, at least for me.

You make it sound probably all too easy! :-) I was thinking along the same lines. I have some decent quality solder paste with lots of flux in it so that's what I'll pre-tin with. I also have a pair of surgical glasses with x20 magnification at hand :-) Thanks for describing your m.o.,

This is a Mega8U2.  Designed in DipTrace.  Manufactured at OSHPark.  Maybe I should have cleaned it before showing it off.   smiley-eek
DipTrace is free to hobbiests up to 500 pins.  You might want to give it a spin.  It's very easy to use.  I know Crossroads and a lot of other people like Eagle but the free version is limited and the pay version gets very expensive very quickly.  DipTrace has lowered pricing for hobbiests.

I hadn't noticed DipTrace until now. It looks mighty. Being a beginner hobbyist I'm a bit daunted by Eagle and all it's libraries. I like the notion of dragging a named IC or component from a library, but the one time I tried my hand at Eagle I came up short of a couple of components and had a bothersome time just figuring out how to fint a component with a similar footprint. That was the lure of Fritzing (well that and the breadboard view), that the components are anonymous until suppled with a value and a footprint of choice. Time and experience should weed those things out, of course, and of course it's a highly regarded piece of software with most. On your recommendation I'll make a point of trying out DipTrace before I try my hand at Eagle any further.
10  Using Arduino / Microcontrollers / Re: Got wrong pitch FQFP MCU - possible to make a save? on: April 10, 2013, 08:50:14 am
Fritzing - you get what you pay for. Not really an optimal design tool.

I'm inclined to agree with you, now more than ever because of my issue with the foot print obviously, but for those out there who're just starting out I'll hasten to add that it's a great visualizer for getting into electronics, with its combined breadboard/schematic/PCB view. I probably wouldn't have begun to design my own boards if it hadn't been for Fritzing. So good for beginners as an try point into the more serious programs like Eagle and such.
11  Using Arduino / Microcontrollers / Re: Got wrong pitch FQFP MCU - possible to make a save? on: April 10, 2013, 02:29:00 am
Hey, I think Crossroads may be right on this.  It's pretty close - the footprint is different but it looks like it is compatible.  This is from DipTrace.  This is the QFP32 7mm/7mm/0.5mm and QFN32 5mm/5mm/0.5mm footprints side by side.   The problem here is that Diptrace doesn't show the exact outline of the package itself so if you imagine a worst case scenario here the QFN's pins might be just inside the radius of the QFP's traces.  But it may be OK too.

Very kind of you to put that image up - thank you for that. By CrossRoad's help it's clear to me now that I'll have to try and get a QFP32 and try and solder it.

A caviat is that QFNs are not as easy to solder as QFPs so keep that in mind.  I hot air solder them myself and inspect them under a microscope.

I shudder at the notion - I've never worked with them before. But there's a first time for everything. Hot air and paste at the ready, then.

I have use Atmel's QFN32 5mm/5mm/0.5mm packages.  Too bad I don't have a PCB with a QFP32 7mm/7mm/0.5mm footprint on it otherwise I would see if it would work out for you.

Again, that's awfully kind of you - thank a lot. I might contact you in the case I need a bit of advice in regards to the soldering - would that be ok with you?
12  Using Arduino / Microcontrollers / Re: Got wrong pitch FQFP MCU - possible to make a save? on: April 10, 2013, 02:19:49 am
Are you saying the 5mm, 0.5mm pitch parts I  pointed out do not fit the 5mm, 0.5mm pitch pads on your card?
Atmega328P-MU, -MUR, -MN, -MNR
http://www.mouser.com/Search/Refine.aspx?Keyword=atmega328p-m'

Hello CrossRoads,

they may fit the board well, being rather the novice I remain merely hesitant for two reasons, the first of which is the labelling in my PCB program (which is Fritzing, by the way). If the footprint fits a so-called "QNF32" then why does it say "TQFP32". This a hugely complex, dedicated piece of software written by experienced people, so when I come across something like this I'm prone to declare myself the ignorant party before calling error on the program. Also the footprint has prolonged pads as indicates room for an MCU with spider-legs sticking out, yet the ones you link to have none of those.

I'm coming to the conclusion that I'd about to venture into my first foray into these leg-less MCU- that, and that I should probably start using Eagle as opposed to Fritzing.

Thanks for all your help, I'm very grateful - if I can get this leg-less MCU fixed on that board (although I shudder in horror at the thought I do have a hot-air station, so...), that's the save I was hoping for when I wrote the post.
13  Using Arduino / Microcontrollers / Re: Got wrong pitch FQFP MCU - possible to make a save? on: April 09, 2013, 04:09:16 am
Ah.  That's more understandable.  But your PCB package is wrong, apparently.  The 168 and 328 don't seem to come in that package at all!  This is a problem with cad-package libraries that you haven't carefully checked, whether they be included from the software vendor, downloaded from a 3rd party, or created yourself...

Absolutely. A valuable lesson. At least I have some nice keychain-boards. Made me glad I put 3 designs on that 5x5 board, so I can cut off the bad parts and still have something to show for my PCB order.
14  Using Arduino / Microcontrollers / Re: Got wrong pitch FQFP MCU - possible to make a save? on: April 09, 2013, 02:51:55 am
That's a 5x5mm TQFP-32 with 0.5mm pin pitches (example drawing:  http://cds.linear.com/docs/en/packaging/TQFP_32_05-08-1735.pdf).  The ATMEGA328P is in a 7x7mm TQFP-32 with 0.8mm pin pitches (datasheet:  https://www.sparkfun.com/datasheets/Components/SMD/ATMega328.pdf page 436).  So you chose the wrong footprint.  I wonder if you couldn't force the 32-QFN 0.5mm version of the ATMEGA328P onto this footprint but I wouldn't count on it.  And they are pretty hard to solder too, though not hardly impossible.  The 7x7mm TQFP-32 isn't going to work out.   You would need some sort of adapter to match it up.

I always print out my PCBs and make sure the components line up before I send them to be manufactured.  Printouts from a laser printer are very accurate.  It gives complete confidence you will be able to solder your parts correctly (assuming appropriate skill) so at least you can have some confidence there.

Hello JoeN,

thanks a lot for you input. I'm coming around to the conclusion that this board will have to go (though will try to fit a 32-QFN on there, might as well) - it's probably not worth the while to try and salvage it. A bummer, but a valuable lesson. Good tip on printing it out - in this case I ordered the PCB and components at the same time, next time I'll get the components first and the board later, as you do.

Thanks.
15  Using Arduino / Microcontrollers / Re: Got wrong pitch FQFP MCU - possible to make a save? on: April 09, 2013, 02:40:29 am
You should pay more attention.  For instance, there are no "1mm pitch" ATmegas.  The LQFPs are 0.8mm.
Also, none of the packages are known as "FQFP"    You've got your 0.8mm "LQFP", and 0.5 and 0.45mm "MLF" (leadless) packages...

Thank you for the suggestion that I pay more attention. I can assure you that the notion struck me the second I opened the box of MCU's to find that I'd wasted money on the wrong units. The "FQFP" was a spelling mistake - thanks for calling it. My PCB program lists a "TQFP32-5MM" package type, which led me to believe I should be able to find an atmega to fit the PCB foot-print. Riddle me this, is the pitch-sizes fixed for the various package types? (in which case I'll deem my PCB program to be rather confusing and poor).

Thanks in advance.
Pages: [1] 2 3 4