The prebuilt step-up LED drivers on Deal Extreme won't work? Have you tried FastTech or intl-outdoor? I know they have a few 1 or 2 AA 1W LED drivers which use the PAM2803 IC.
If you're in the US, I can give you a link a to US vendor that stocks them.
Excellent question. Deal Extreme has a bunch of items like http://dx.com/p/1-5v-350-400ma-constant-current-led-driver-board-for-diy-flashlights-128096 which may well be exactly what I want, but the description is so poor I can't tell. "Voltage: 1.5V" do I just assume they mean input voltage and it outputs a higher voltage? Even if so, what is the maximum output voltage, the maximum input current, will an Alkaline AA even be able to power it? Does it have to be 1.5 volts, can I use 2 cells to lower the current needed? It really is frustrating. Maybe I should just order something that looks promising.
I took a look at the datasheet, PAM2803 based modules could be good. Maybe that's what a lot of these modules use, they seem cheap enough. I'm located in Canada.
I'll show you PWM in action, it's a constant 5v, what you vary is the overall current the 555 will chop up the load giving the LED a break and you use less current, 555's not going to be that efficient.
I was testing this cheapy oscilloscope i bought off of ebay so i tried it with PWM (which can be done with a 555 or an Arduino)
That looks like a normal 5mm LED. How will that circuit help me drive a 350mA LED? Also, I don't need to dim the LED.
I was watching a video at adafruit discussing a 4-AA battery pack for charging an iphone. Bottom line - you can only get 500mA from AA battery.
I suppose if I use the boost regulator off 2-AA's that won't be a problem as long as efficiency stays above 70%. 3V 500mA is 1.5 Watts. But I'm okay with 2 batteries, so not a problem.
" Also, ideally I'd like to switch the LED as fast as possible (clean square wave in the 10's of kHz range), which the transistor solution lets me do."
Not really sure what intended here - unless it was the switching speed of a boost converter:
"The LTC®3490 provides a constant current drive for 1WLED applications. It is a high efficiency boost converter that operates from 1 or 2 NiMH or alkaline cells and generates 350mA of constant current with up to 4V of compliance. It contains a 100mΩ NFET switch and a 130mΩ PFET synchronous rectifier. The fixed switching frequency is internally set to 1.3MHz."
the LTC3490 looks quite nice, its a bit expensive in small amounts and of course a pre-assembled "typical application" module would make things easier, but it's the best option so far. I think I'd have to use 2 cells though. With one, the LTC3490 efficiency drops to 50% and drawing 1.5 amps from an alkaline AA will drastically reduce its capacity. That's not a huge problem though, and as far as your later post, the LEDs I have in mind require 350mA in the 3-3.4V range, so it appears this is the right chip for what I'm doing.
I'm actually thinking of a few projects that involve switching the LED, the more complex involves carrying data. Imagine people carrying flashlights and I can identify them by a signal carried on the beam. Like an IR remote but visible with a high-power LED. The simpler project is a stroboscope, an external trigger turns the LED on for 50 to 100 uS.
I'm not familiar enough with these power supplies, can I just use a transistor to switch the output and when I want to turn the LED on the power is there and stable fast enough?
Unless I'm mistaken, I think he asked for a PWM solution?... there are plenty of other ways including a switching regulator for a couple of bucks off of ebay (this is the most efficient way though for the price) but feel free to play with the 555 if you want a cheap solution to make your circuit more efficient.
I still don't understand how PWM helps me get a constant current to the LED.
Look into constant current drivers vs straight voltage with current limit resistor.
That's what I'm looking for but all the modules I can find are either 12V or 85-240V inputs. What I want must exist judging by the number of cheap flashlights that use a single cell to power a 1W LED. I've spent a while with google, deal extreme, and aliexpress, but if you can point me in the right direction it would be helpful.
You can use an LM317 Adjustable Voltage Regulator as a constant current driver. Google: LM317 constant current
I understand these require at least 3 volts higher in than out even as a constant currant driver and as linear regulators just dissipate the extra power, so they're not very good for battery powered circuits.
cheapest solution would be a 555 chip as PWM ..... that way a small potentiometer could be used to vary the brightness.
I'm not sure what you're suggesting. I don't need to vary the brightness, I'm looking for a power driver. A 555 can not supply 350mA (a quick search seems to show 200mA, 600mW), and it's not cheaper than using a PWM pin on the arduino that's already controlling the project.
I have a project where I'm using a 1W, 350mA LED and the entire project needs to be powered from AA batteries (alkaline or NiMH). Is there a good way to drive the LED?
It's working right now using a transistor to switch the power and resistor to limit current to the LED, but burning half a watt on a battery powered project is pretty bad.
I've been looking at the little power supply boards online but they all seem to want 12V in and power 1-3 LEDs in series. I'd rather use as few batteries as possible. Also, ideally I'd like to switch the LED as fast as possible (clean square wave in the 10's of kHz range), which the transistor solution lets me do.
OSHpark and batchpcb are both extremely overpriced. If I just ignored the issue I posted about and wasted 75% of the board area on seeedstudio/itead, I'd still get 10 boards from them for less than 3 boards from OSH or batch.
I wonder if anyone can offer a suggestion where I can get some non-square PCBs fabricated. I need some boards that around 100mm x 20-25mm. I've used seeedstudio for boards many times and I very much like their service but they seem to be most suited for square shaped boards. It seems wasteful to pay for 100mm x 100mm board (100x50 is strangely the same price) and then give them a board that's under a quarter the size.
I've considered panelizing but I don't have a good way to separate the boards.
I used 27K for the ISET resistor. 1K may be too low.
My guess is this is the problem. The datasheet says it should be at least 9.53k which sets the current at 40mA. The current drivers are set at 100 times the current through this resistor and 40mA is the limit for the device.
1 and 7 only use 2-3 segments, any other digit uses more, so it does explain your symtoms too.
What makes you think your monitor is displaying the "exact" color you think it is? For one thing, they need to be calibrated http://spyder.datacolor.com/
Besides that monitors have a certain colorspace with better monitors able to show more color gamut. Viewing angle effects the color (much more variation on TN panels than VA or IPS panels).
If you show the same picture on 2 different uncalibrated monitors, you'll get very different results.
As others have said background color makes a huge difference in perception. So do viewing conditions. When calibrating a monitor it factors in ambient light. When printing pictures for exhibition, my print software compensates for the ambient light the picture is intended to be viewed in.
How do you intend to generate the colors on the LED, run it at full power and PWM it? That's relying on the performance of the viewers eye to render the color and you're really displaying nothing remotely like the color on the screen even if you manage to get it to look similar.
Even calibrating something as simple as your white balance, getting pure white and pure grey is very hard to do.
For example, use a wallwart 5V power supply, delete the 7805 regulator, add IO connectors that are more secure than plug-in headers, etc.
I would be careful with that advice. Modern switching wall warts should be fine, but if he gets a cheap, old linear based one, it could easily give 8V no load and fry his chips (yes, I made that mistake in my pic days).
Why not a solder pad on board and solder the bolt-head to the board.
I should test this before rejecting the idea, but my understanding is solder won't stick to galvanized steel or whatever they make the bolts out of. Any idea if that's true? Maybe if I find some brass bolts?
Thanks for the suggestions anyway. At least you won't have my issue as badly because those dips are easy to drop into a working project with a socket or breadboard. This is my first scratch-built SMD project, I never realized what a pain it would be to debug.
I ordered a 5 pack of soic->dip adapter boards from ebay, so I can drop one of the 7219's into my breadboard. The dip device I have is from maxim's sample program; can't get more reliable than that.
It's going to take 3 weeks to get the adapters, so now I'm debating also ordering some more 7219's from a different supplier so at least I'll have them sooner. I love what the internet has done for this hobby in terms of price and selection, but hate what it's done in terms of slowing down the process.
The code is working fine with a dip-based setup on breadboard. Both the sample that came with the ledcontrol library and my own code. Even using the same arduino without reprogramming, just unplugging the boradboard and connecting the pcb.