Ok guys, I'd like to build my own LED light ... but have no idea how to go about it.
The light I have in mind would be simple ... just wires, LED and battery(ies).
Doesn't have to be particularly bright.
Don't want a flashlight. I was just thinking about building something that would function as a cheap (emphasis CHEAP) night light in my RV. Something that would burn say a week on a couple of AA batteries. Maybe a 9 volt.
I have an industrial strength soldier iron from the 60s.
No electrical or mechanical ability.
Is this going to be a challenge or what?
But hey, it will be my first homemade light!
I need a shopping list and simple to follow directions.
once you start actually <font color="blue">doing</font> it, it will make a lot more sense. before i started mods, i had no idea what i was doing, once i got all the parts, i said "wow, this will be easy!"
basically, get some leds, get some batteries, and try using the leds with the batteries [img]/ubbthreads/images/graemlins/grin.gif[/img] (sound too difficult? [img]/ubbthreads/images/graemlins/grin.gif[/img])
then, once you figure out what kind of batts you want to use, add a switch between the batteries and the led(s), and once you have that worked out, then you can find a nice home for it! [img]/ubbthreads/images/graemlins/grin.gif[/img]
Just get some and play? And does every LED need a resistor? Does a resistor make the LED run longer, brighter?
I'm not as dumb as I sound.
Well, on second thought, yes I am.
When I read a PaLight will shine in the "find me" mode for two years ... I started thinking ... boy, if someone could come up with a simple LED nightlight illumination device, that would work for long period of time on a couple of batteries.
I appreciate the response!
RV'ers spend a lot of time off the grid, so making something burn a long time, with a little illumination, would really help!
be carefull with radio shack leds. many of which they have in stock are rated for 2.4 volts. running 3 cells (4.5 volts) would fry them quickly. there white led they carry is an awfull color of purple. but if your looking for any color they carry, just look on the back of the package for the vf (forward voltage) if its 2.4 u can run it off of 2 alkaline cells slightly overdriven.
a suggestion would be to buy a nicha led (there rated @ 3.6volts) run it off 3 cells with a low ohm resistor for long life, or straight from the cells for more brightness but a little less life.
You can easily damage or destroy a 5mm LED with excessive current, even on 3 alkaline cells at 4.5 Volts. Remember that most 5mm LEDs are rated for nominal 20 mA service. A single LED on 3 fresh D-cells could conceivably be passing 5 to 10 times this current, or more. That could quickly destroy or at least damage your LED.
Use a current-limiting resistor with 5mm LEDs in cases like this. They are easy to compute:
(Supply voltage Vs - LED forward voltage Vf)/desired current in Amps = resistor value in Ohms.
Example: one 3.4V LED driven by 4.5V, 40 mA current:
(4.5 - 3.4)/0.040 = 28 Ohms.
Choose the closest standard value.
This resistor is connected in series with the LED and power supply.
Power dissipation will be:
Resistor value in Ohms * (run current in Amps)^2 = Power dissipated in resistor, in Watts.
In our example, P = 27 * (0.040)^2 = 0.043 Watts. A good rule of thumb is to select your resistor with at least twice this power dissipation. In this case even a 0.25W resistor would work
Luxeons can in some cases be directly driven without current limiting but keep heatsinking in mind! (and 1 Ohm or so of resistance in series with a Luxeon is a good bit of insurance)
best of luck,
p.s. - I have lots of bright LEDs if you need some, posted over in B/S/T. Much less $ than Radio Shack. If you want some ideas about what you might build with LEDs just take a cruise on through Modified and Homemade. I have a decent collection in the link in my sig file too.
Perhaps the Brinkmann Legend AAA mod would be the easiest?
Just get a Nichia NSPW500BS,its a 4.0v 30ma rated white 5mm LED at 6400 mcd, most modders here have a ton of those, fairly cheap and very bright. If I can't find the mod instructions here on CPF someone else will, or the Solitaire mod, I only made a couple hundred of those mods, very simple and reliable, uses a 12v 21/23 battery.
What I'm looking to accomplish is to build a little LED nightlight ... for say, my RV bathroom ... so that when I'm dry camping (without electricity and trying to conserve the rv batteries) ... after my eyes adjust, I can see well enough to not stub my toe whilst doing my business.
Doesn't have to be bright ... but it would be nice if it would last a couple of months on a couple of batteries.
well, if you want to experiment, a single nichia LED coupled with a variable resistor and 3 d cells will attain a VERY long runtime, and dimmability. it will also be fun to experiment with new found light-building-skills.
if you want simple and inexpensive, you could get a palight onestar from brightguy for about $15. remove the lens--this will give a wonderful smooth flood of light. if you are going to use it just as an area light, you could leave it set on low. should give nice long runtime. heck, even the "always on" feature just might give enough light to do your business. the square shape allows it to sit anywhere, and you could velcro it to a surface if needed.
you could also use up the supplied 9v battery, then throw in a lithium 9v, which has twice the capacity as a standard alkaline--and better cold resistance as well. lithiums ar pretty expensive, though.
want incredibly long runtime? remove the 9v. buy a 6 battery AA holder (or fashion a holder yourself) and connect it to the pal head. though it would be significantly bulkier, it could still be created in a clean manner.
got money? get an eternalight elite x-ray for around $50...you could leave it on the lowest setting for months.
Be CAREFUL if you intend to run LEDs without current limiting. This is a simple matter and stands to improve your mods, improve the life of your LEDs, etc.
At the very least you should measure the current in your built system with fresh batteries. Seriously - measure it. At least this way if you are getting ridiculously high currents you can install a resistor and save yourself some battery life as well as the life of your LEDs.
It makes the engineer in my chuckle when I hear about "direct drive" non-Luxeon LEDs. In many cases this is simply a great way to drain your batteries that much sooner and induce damage in your LEDs that much sooner.
For example, my Matchbox Mapasaur (find this by clicking the AB workshop link in my sig) uses one Nichia S-ranked 9200 mcd LED with reflector in a tiny 3AAA battery box. It was designed to run on alkaline or rechargeable AAA's. It has an 8 Ohm resistor in series with the LED. Without this the run currents are simply far too high - and nothing beneficial at all to running the system without it. No consequential increases in brightness, but reduced battery and LED life.
White 5 mm LEDs particularly do not appreciate over-current operation. Do this for long and you will start to have a much dimmer and bluer light source as the phosphor on the LED die begins to deteriorate.
Ab, your creations are what inspired me into thinking (foolishly) that I could create my own simple LED. Trouble is, all of yours put out WAY too much light (I know, I know, that's the name of the game). But I'm talking about a little bathroom illumination here. No need to read while I do my business!
Ok, since no question is too stupid ... how to I connect the 4 led's together ... in parellel or in series?
Connect all the positives together and all the negatives? Or connect positive to next negative and next positive to next negative.
And remind me once again, is the long side the positive or the negative?
Since this is the first experimental item in the "learning stage," LED from RS will do okay. While learning, there is no point is wasting good LEDs, is there?? [img]/ubbthreads/images/graemlins/grin.gif[/img]
RS LEDs are not for flashlights. They were intended for panel mounted (or PCB mounted) indicator lights. RS is losing out and is slowly going downhill. I expect them to be out of business in less than 10 years (being generous).
I'm ranting a bit, since I remember RS in their glory days. [img]/ubbthreads/images/graemlins/wink.gif[/img]
This seems a fair enough request, I'll have a lash or two at it. I'm going on the assumption that this is intended to be both a practical project and a learning experience and that we should start out simple.
I went to my local RS to see what was offered. Hopefully, you'll have the same parts or something similar. I went looking for high output ('very bright') red LEDs and bought one (part number 276-0086) a 5000 MCD (at 20 mA) "jumbo" (therefore narrow beam). A bit pricey at $2.59 but knowledge ain't cheap, right?
The idea behind starting with red is the low forward (operating) voltage, typically 2.0 Volts more or less. This means we can drive it from a two cell battery (say two D cells for long life). Using whites would need another cell (raising the battery total voltage to 4.5) to deal with the 3 plus volt Vf.
First off, don't buy into the 'you don't need resistance' idea. It's simply not so. Resistance is what sets the current, without it current would 'run away' at voltages above Vf and the LED would be destroyed. Those who 'direct drive' are in fact still using resistance, the internal resistance of the device (one to several ohms), battery (a dozen to a few hundred miliohms per cell depending) and the various contact resistances (often into the few ohm range) alone. Such systems are characterized by very large (read 'wasteful' in this use) currents on fresh batteries, quick rundown to a long period of dim light as the last bits of energy are drained. Adding the correct resistance allows us to limit the initial current (adding greatly to battery life) and control it's 'mid life performance' as well. We need to decide how much to add.
A good place to start is to pick a number that will give low current and see what we get (pun intended). Let's say 1 mA (one miliamp, a thousandth of an amp, 5% of the typical 20 mA rating. First a bit of subtraction. The total battery voltage (3 Volts for the case of two 1.5 Volt cells) less the forward voltage (operating voltage of the LED at that current, say 2 Volts), giving us 1 Volt 'across the resistor'. Now for the division. Ohms law tells us to divide this voltage in volts (1) by the current we want in Amps (.001) to get an answer in ohms (in this case 1000). This resistor is so much larger than the internal and contact resistances that they can be safely ignored.
So, if we take our two cell battery (holder advised) and put our LED and resistor in series with it (short LED lead to the more negative side) we should be Jake. Order doesn't matter, the battery, resistor and LED can be hooked up in any order as long as the battery and LED polarity are watched. Hooking the LED up 'backwards' is safe as the total voltage is under the typical 5 Volts the device will tolerate reversed. In the example I built with these parts today I got what I think is a usable amount of light (easily enough to find your way about IMO), but you'll need to judge that for yourself.
We can expect nearly full capacity from our battery at such a low rate, more over as the cells discharge and their voltage goes down the current will follow as the 'voltage across (and therefore current through) the resistor goes down'. A quick estimate (conservative) gives over 2,000 hours from AA cells, some 18,000 from D cells. Roughly 3 months and two years respectively. If you want more light, lower the resistor. Using 500 ohms (actually 510 the nearest standard value) will double the current (and light output) and cut the lifetime in half.
You might consider a 'turbo switch' to boost the light when you need it (say like when you're trying to navigate in the bathroom). Simply put a second resistor in for the higher current. Adding a switch and say 51 ohms across the 1000 ohms already there will raise the current to 20 mA when needed. This resistor could also be placed in series with the 1000 ohms (making the total 1051 ohms for dim) and the switch used to short out the 1000 ohms (bringing the total to 51) for 'turbo mode'. You might consider a micro switch mounted to the battery pack and pressing down when the light is normally rested on the counter. The contacts (we want to use the 'normally closed' contacts which would be open, no connection, when the switch was actuated as when hitting the counter) to automatically switch to bright when the unit is picked up or turned on it's side. That's what I plan at any rate on the one I'm building. Makes it easy to find in the dark and a 'no brainer' to pick up and use.
That should at least get you started.
If you're serious about fiddling about with this sort of stuff, 'we should talk'. How you fixed for mail order where you are? Jameco Electronics <www.Jameco.com>, might be just the place to stock up on cheap electronic bits. Let me know if you're interested and I'll see if I can cobble up a list of suggested parts.
Yep, that one would do it. Half a Watt is way more than we need (formula is Volts across times Amps through, one Volt, .001 Amp, 001 Watts), quarter Watt units are cheaper, smaller and still way more than we need. I'd recommend part 271-1321. You might also consider a lower value at the same time for fiddling with more current (and lower battery life) easier. Say a pack of five 100 ohmers, part number 271-1311?
Once you set up the basic circuit (one side of the battery to one resistor leg, second resistor leg to LED leg, other LED leg back to battery), a simple 'series' circuit where the electrons must flow through each element in turn (no parallel paths) you're set up to fiddle. Watch polarity, short LED leg to negative. Adding a second 1000 ohms in parallel ("across") the first will double the current to 2 mA since each resistor will pass one (for a total of two). Likewise adding a single 100 ohms raises the current one volt divided by 100 ohms for an additional .01 Amps (10 mA). Since light output is nearly linear at these levels, light output will go up 'ten times' as well (total is now 11 mA). A second 100 ohms, added to the first and the original 1000 ohms raises the total current to 21 mA and so on.
These numbers are only approximate, of course, but typically this level is 'close enough' for electricity. "Only Engineers sweat the last 10%". It's paying no attention to them at all that gets you in trouble. To further refine it we'd need to actually measure our LED (at a couple of currents in fact) and our exact battery voltage (which of course is changing all the time) and perhaps even how accurate our resistor value is. Given reasonable margins we can safely ignore such fine points in the general design.
It's worth noting that this gives you excellent *current* control. And current control is how *all* the LED makers spec their parts. Not a single one will support fixed voltage (i.e. 'direct drive'). IMO they ought to know what's best for their products.......
Again, if you're 'mail order able' and interested in fiddling a bit with this (IMO kinda fun) stuff, speak up. We can look into a modest (say $50?) pile of parts, meter and related bits from Jameco and see how much of the (simple in small bites) electrical magic we can unravel via internet.....
After thinking (or what passes for it) about this a bit, I'd like to change my advice. Just buy the RS 1/4 Watt assortment, part number 271-308.
If you've got a few extra bucks and want to make fiddling with this stuff easy get a set of clip leads, part number 278-1157 should do nicely, or perhaps 278-1156.
And I don't buy that 'way over my head' bit, even a little bit. This isn't swimming, you don't drown. You're just not there yet. I've taught this good stuff for 25 years and change, and I'm here to tell you it's not that hard. Taken in steps at least. That's the way adults learn. Der younger learn by faith or rote. As adults, we build skills in steps. Understanding on understanding, a whole structure.
Have some faith in me as well as yourself? Buy another RS part, 275-016. A small 'micro switch'. I mounted one on my battery pack and it works just fine. Two levels; two year low level resting on the counter, one month (high output) when you pick it up. My money says if you get a few bits and fiddle a mite you'll wish you had one.....
In a way I wish I'd already sorted out the posting of photos, I'd show you what we're talking about..
Try this for your body of your light I think it will work well for youand they carry them at Radio Shacks cheap.
This is a four AA cell battery pack with a little on/off switch on it already. Open the case with a little phillips screw driver.
Remove the other screw from the little plate that covers the switch area. Pry that plate off carefully with a pocket knife or small screwdriver watch the melted plastic and do a little at a time.
While pushing the wires back into the hole pullthat electrode that has the red wire attached to with some niddle nose pliers. Turn the electrode upside down and side it in behind the other end with the spring on it.
That battery space you have left there is going to give you plenty of room the work with. If you would like to add another switch with more legs for power out you can set up more LEDs to have more light than one LED but you will have to figure the resistance for the other group of LEDs. Try this link for any calcs you will have to make with your LEDs. http://linear1.org/ckts/led.php
This should be a cheao way to ste up your first home made flashlight. Have fun! [img]/ubbthreads/images/graemlins/thumbsup.gif[/img]