This is my first project that didn't come pre made from a kit so excuse the easy questions. I want to power a headlight (25 20mw white leds) that are on/off, two tail lights that are the same lights but in red, but divided into give serial groups each so as to make arrows that can be animated. Also want to be able to turn on those 25 red leds at half power for all and full power. Also need a switch for each set of lights (headlight, left, and right turn) and a flex sensor for the brake lights to activate. This seems like close to the limit for a standard arduino. Personally looking at a pro mini.
Can I run 25 20mw leds off one pin?
Is there a way to dim leds without pwm? I have an idea to jump together all 5 zones of tail light to turn them on at half brightness via pwm but now am thinking if I do that they'll all just be wired together into one group.
Please give any insights into this project. I'd like to give my bicycle a motorcycle worthy lighting setup. Would 25 of these leds be too bright or not bright enough for night riding?
Thanks.
Can I run 25 20mw leds off one pin?
Half a watt of power? No.
Is there a way to dim leds without pwm?
Yes - only light half of them.
Would 25 of these leds be too bright or not bright enough for night riding?
Not bright enough - see reply 1.
"Can I run 25 20mw leds off one pin?"
Sure - just use a transistor to switch them on/off. Arrange in parallel strings (ex 5 strings of 5 in parallel from a 12V source).
Use a boost regulator to get the voltage up & the current down - for example 5 strings at 20mA each vs 25 LEDs at 20mA each.
Dim LEDs with on-chip PWM, or just turn on/off with digitalWrites at whatever speed you can write. Ex blink without delay, on for 10mS, off for 10, or 20, or 30 etc.
If using high brightness LEDs (4000-8000mCD each) will be pretty bright! www.superbrightleds.com for reds anyway. Don't know if that would cut for a headlight, especiallu giving up the "focusing" that a lens provides.
Grouping into arrow segments - also easy, just need a control pin per segmet.
Can drive segments with discrete transistors, MOSFETS would provide lowest power drop thru the transistor. Or go for easier building & use ULN2803 as the LED driver.
Switch, no problem, easy to read a contact pulling a pin to ground.
Flex sensor, need more info on what that is.
Promini gives you 20 I/O to play with (need 2 pull 2 from the middle of the board, I do it all the time), make a list of your I/O needs and see how many segments and switch closures you have. I built up a lot of prominis into fencing scoring machines controlling a whole mess fof displays.
I have 10,000mcD white LEDs with small viewing angle (15-20 degress I think), blindingly bright - just 3 of them at 2-3mA, 15-20mA was too bright to be pointed at you!
Make sure you allow for aiming the headlight to pass state safety inspection.
Also consider environment-resistant packaging, oil/gase resistant sleeve/jacket on wires, etc.
Thank you all for the helpful replies. I've had some days to read, reread, and consider and research different options and changes to the idea. First I'll explain a little more what I'm trying to do. Its not all practical just a reason for me to build something that I'll find useful.
I'm trying to put a bright headlight, turn signals and tail lights on a bicycle. In general I want to look like a motorcycle so people are less likely to run me over or zoom past me at 50mph. The headlight should therefore be as close as possible in brightness and angle within reason. I looked at a Luxeon Rebel high power LED on sparkfun (3VDC, 350-700ma, 90-160 lumen) but they also have a breakout with 3 of them (call it a triple play) plus available wide (40 degree) lens that fits right on. There is also a driver built to fit with the breakout ($24! for what?). But after all that I expect I might have heat issues. What to do about that? Enclosure for light so if it rains it doesn't get wet?
As for the tail/brake lights, still keeping with the bright LEDs (I don't feel I got an answer if they would be overkill and I should just use regular red LEDs) I might go for using a shift register such as a TI TPIC6B595 that allows 150mA per channel, 500mA total, running them in a daisy chain and addressing each LED individually. It would add a few bucks to the total project but I like to be able to address each light one by one. Question is can I do that, as in though there would only be 160mA of current on each IC, being that #2 is pulling from Drain7, does that mean there is 160mA moving through one pin on IC one when in a daisy chain? I thought you could run them in series and the arduino could move through them one by one as if it was a 64-bit shift register.
I also have to put the proper resistor for each LED then, correct?
I'm not sure how I'll be powering this just yet... either a small rechargeable battery or I'll try to tap into the bike's 36v battery (amped bikes kit) for power.
Assuming I can get all the tail lights on, individually addressable, I can easily turn off half of them. I would rather dim them for a few dollars but I don't know if that would work down all those ICs. I saw a PWM switch but I don't know enough about it to go much further.
Final note about the tail lights. The end goal would be to use a switch (or possibly photocell, just for kicks) to turn on headlights an tail lights (half power). By some method, turn on tail lights at full power when I pull one (either?) brake handle. Lights are 9,000mcd at 10 degrees BTW. And when I press a button make animated arrows. Easy if point addressable.