I have an off-the-shelf red LED headlamp (Energizer?). Trouble is, it's quite bright, and it's actually white/red depending on which way you slide the switch and I know I'm not the only one that's gone bright white momentarily flicking it the wrong way.
Been thinking about a way of either dimming this one, or making one from scratch. Would be nice to have a small box, maybe with 2 options - one with a soft/diffuse red light so I can see the keyboard, sockets etc on mount, and a beam or more directed light for walking around.
Any suggestions, ideas, shopping list from Jaycar?
Open the one up you have (small philips head scewdriver needed), find the resistor that feeds the white leds and cut off one leg.
Find the value of the resistor in series with the red led and increase the value, some experimentation may be needed but you'll end up with a red led torch with the brightness you want and longer battery life.
I seem to remember Ponders mentioning that they will still work with just one battery, i.e. removing one (and replacing with a suitable dummy) will dramatically reduce the brightness, negating the need to adjust the resistor value.
Took one battery out and it didn't work. I connected up the 2 terminals of the removed battery and it did work, and was dimmer. So that may be an option.
I opened her up and see attached photo. I'm thinking now that I could swap all 3 resistors, and the 2 outside white LEDs for red ones, so have dim and brighter option.
Questions:
1. The 2 outside resistors I was expecting to be the same, but they're not. From my limited understanding of colour coding, one is 22 ohm, and one is 55 ohm (I think they're green, not blue). The middle one is also 22 ohm. How do I figure out which ones to swap?
2. Assume that to halve the brightness, double the ohms - so 44 ohms etc? How low can you go? Limits?
3. How to identify the white LEDs and which red ones to get?
1. The 2 outside resistors I was expecting to be the same, but they're not. From my limited understanding of colour coding, one is 22 ohm, and one is 55 ohm (I think they're green, not blue). The middle one is also 22 ohm. How do I figure out which ones to swap?
White LEDs typically have a higher forward voltage than red LEDs, so, without seeing the circuit, I would say the 56ohm (green and blue ) will be for the red LED.
Quote:
2. Assume that to halve the brightness, double the ohms - so 44 ohms etc? How low can you go? Limits?
No limits when going that way(dimming), yes doubling resistance will halve brightness.
Quote:
3. How to identify the white LEDs and which red ones to get?
Turn it on?
Any red will do. They will be different to the pre-existing red one so grab a hand full of resistor values to play with brightness.
Or, replace all three with red then replace all three resistors with same value.
There are differences in colour in the red LEDs, if you go to Jaycar they should have an LED tester behind the counter and they should be able to demo the various red LEDs for you. Some are more orangey, but from memory(been a while since I managed a store) there was one there that was a very nice deep red.
Also, all three resistors look different to me, if you type out the colours here I can tell you their values.
FYI RS components is free overnight shipping for any order (confirm for single resistor, but should be free), probs be way cheaper than Jaycar.
FYI Soanarplus is supplier for Jaycar and uses the same catalogue numbers. Shipping cost works such that best to buy a few things at a time, not just one resistor.
Assume a 10mA forward current @ 3v forward voltage (conservative) and use this calculator to calculate appropriate resistor value:
If LEDs are in series, multiply 3v forward voltage by number of LEDs. If LEDs are in parallel, multiply 10mA forward current by number of LEDs. Ideally, each LED has its own resistor.
just FYI.
However, you can use resistors they have used and multiply by a factor to reduce brightness. Eg if you want half as bright (Theoretical), simply double the resistor values they have used. That way you can avoid the led calculator altogether.
I say theoretical because eye response to brightness is logarithmic
Now that I'm at work I have time to look things up
The deep red LED at Jaycar is cat# ZD-0152.
It's wavelength is 660nm (very close to Hydrogen alpha ) where most red LED's are around 620 - 630nm and look kinda orange by comparison.
Cheap at only 65c each.
Now that I'm at work I have time to look things up
The deep red LED at Jaycar is cat# ZD-0152.
It's wavelength is 660nm (very close to Hydrogen alpha ) where most red LED's are around 620 - 630nm and look kinda orange by comparison.
Cheap at only 65c each.
Or get 5 for $1.25 total @ 660nm, 650mcd brightness, proper datasheet available to show Vf/If curve, and free next day delivery Australia wide, decent brand.
Yeah or do that.
I'm aware of RS, have had an account with them for close to 30 years, but Troy did mention in his OP about a shopping list for Jaycar so I had assumed he has one reasonably nearby and he's not averse to going for a little drive.
Another benefit is he can compare before commiting.
Anyway, I was only trying to help, didn't realise it was a competition.
Good luck with it Troy,
Yeah or do that.
I'm aware of RS, have had an account with them for close to 30 years, but Troy did mention in his OP about a shopping list for Jaycar so I had assumed he has one reasonably nearby and he's not averse to going for a little drive.
Another benefit is he can compare before commiting.
Anyway, I was only trying to help, didn't realise it was a competition.
Good luck with it Troy,
haha no competition, good to throw all the ideas out there . Only thing Jaycar is good for is trying stuff out (but that is for me anyway).
If you're bothering to hack your torch, you could certainly wire it with a low resistance and a high resistance selectable by the slide-switch (for two brightness settings), but why not:
a) snip the resistor to the white LED so that it won't turn on accidentally, and
b) insert a variable resistor in series for the red leds, so that you can dial the brightness up or down to your taste.
If you're electronically-challenged, I just use one of these on a cord around my neck: http://shop.australiangeographic.com...3l4xoCtTbw_wcB
It is red only, so no worries about accidentally dazzling yourself, and has two brightness settings, selected by a simple thumb-clicker - one click turns it on bright, a double-click turns it on dim, and a single click turns it off from either mode. (It also has flashing and signalling modes, but I don't use them.)
Simon is correct. Jaycar was mentioned because I'm familiar with them, and they're pretty handy and quick for me to get to. I have no issues travelling there, and have never found the queues or staff a problem. In the extremely small volumes I buy from there, $0.65 each vs 5 for $1.25 is neither here nor there.
Julian - thanks for the link. Will look into that as another option.
Buy a cheap 3v flashlight with bulb. Disassemble bulb, breaks the glass sphere and solder a LED with the color you prefer (I, green) using the socket. you need only watch the position of the LED because it has polarity.
And remember to change the batteries in three years, before leaking acid.
) will be for the red LED.
