But unfortunately I can't use PWM, this LED is destined for a circuit that the Arduino won't have control over. It won't need to be dimmed in the traditional variable sense - just preset to an intensity that doesn't cut through things.
Blue LEDs come mostly in transparent housings; of course other colors as well, but we are used to green,, red or yellow LEDs in scattering colored housings. This makes an enormous difference in luminous density.
@Jack,
Hahahah, that's a proper DIY hack right there mate. Excellent.
@deSilva
I'm sure I asked for a diffused casing but they gave me clear. So it pumps out a huge amount of light in an upward direction (imagining the LED is plugged into a breadboard) and not that much in the other directions.
Unfortunately I was stupid enough to be leaning over the breadboard when I plugged the thing in with only 330r. I was quite shocked (read: blinded) at the power.
Got myself a new pack of resistors and managed to mock-up the circuit without further damaging my eyesight.
Rather than create a new thread, I was hoping someone reading this wouldn't mind confirming if this is safe for the Arduino.
Basically, I want
Arduino digi pin 12 to be "disconnected" (or whatever the term is for the not-high-not-low state); this means that 5v flows through the 100k resistor to the LED and it's a bit dim.
Then, when the Arduino decides, it can send pin 12 high and give the LED a boost by applying voltage through the 10k resistor to a bright state (although not corrective eye surgery bright). I worked out that 10k and 100k resistors in parallel end up giving me about 10k resistance in total.
The bit that concerns me is switching the pinMode of digi 12 so frequently. Is this likely to cause problems?
Here's the circuit and a bit of test code (it all works).
Instead of that 100k ohm path to keep the led on dim you might just want to see if turning on the digital pin's pull up resistor might work. That would save you a resistor and some wiring.
void loop()
{
pinMode(_LEDBOOST, INPUT);
digitalWrite(_LEDBOOST, HIGH); // this will power the led with the
// internal pull-up resistor at around 40k-50k ohms
delay(5000);
pinMode(_LEDBOOST, OUTPUT);
digitalWrite(_LEDBOOST, HIGH);
delay(5000);
}
Unfortunately, the supply line running through the 100k resistor is kinda part of an existing circuit that needs to stay. (Although I think it currently only has about 120R in there so I'm ramping it up). Essentially, I'm changing a red LED in a power-on/reset circuit, to a high power blue one and wacking in an extra feed to boost the LED luminosity when the Arduino (which has been inserted into the box) is influencing things.
Obviously there's no way you could have known all that.
In this circuit, I was trying to simulate the existing part of the circuit and then add in the new part.
We have a cooker with a blue LED display and the colour appears to cause excessive flourescence which I feel is possibly a spectral sensitivity peak of the human eye.
What you are seeing is the fact that blue light is bent less during refraction than any other colour. Consequently is is more difficult for the eye to focus blue light. This explains why blue snooker balls appear to have a glow round them.
There used to be a dolly blue factory in Backbarow in the English Lake District.
The surroundings were covered in the stuff and this gave everything a soft edge that was most unpleasant to look at. It has since been cleaned up and now you would never know.
Finally a photon of blue light has more energy in it that a photon of any other colour so this gives a greater kick to the retina when on impacts on it.
@Groove, ok so i have wierd eyes that are extra sensitive to blue and purple, now that i've had cataracts removed i see the world in a whole new light so to speak including sensitivity to ultraviolet which is normally blocked by the human eye but not by the synthetic lenses they implant
@ GrumpyMike,
I remember the dolly blue factory (my granny's shop used to sell it in little muslin twists) and the river below the factory also ran blue!
Difficult to imagine that level of obvious pollution being tolerated these days.
@P18F4550:
I once read that cataract patients were employed as spies to read morse from UV lamps from subs offshore.
(Don't know how true that is, nor can I remember where I read it!)
I haven't heard that one, alot of people who have had this done say colours are more vivid, im used to it now but to start with everything looked purple for a while even clear blue sky