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LED Question

An idea came to me in the night. The supply voltage is 7.5 volts. The LED's are 1/2 that. So two in series is perfect. I took two soldered them together with about a 15 degree outward angle between them Then soldered hook up leads to the other legs and cut them all the legs short. I then pulled them back to the rubber boot and plugged the boot into the mounting hole making sure the LED's were horizontal. I also sanded the domes to make them somewhat wider angle and more defused. The results are very favorable.

2-leds.jpg
 
Hey Graywolf,

Download this datasheet and look at page 6. It shows a forward voltage vs. current I-V curve. It's similar to all LED's that don't have a built in series resistor. You see that there's a sharp rise in current after the LED starts conducting, even when the voltage across it doesn't become much larger. Unless a resistor is deployed, the LED will burn out due to excessive current. If your supply is just high enough to support two LED's in series, I'd rather have them all in parallel, all with their own series resistor.

<http://www.avagotech.com/pages/en/leds/high_brightness_through_hole_lamps/round_5mm_white/hlmp-cw15-tw000/>

This one is not suitable, as it's pattern is too tight for your floodlight type of application. I've seen ton's of people make the assumption that LED's are connected like incandescent lamps. The I-V curves are almost opposite.
 
I know I need current limiting. At least if I do not want to be replacing them rather often. I think I will measure the current without a resistor just to find out what it is.

But to make EchoWars point, notice how much brighter the output is in the second photo compared to the earier one. The earier one has one LED with a limiting resister/voltage droping resistor, the later one has 2 LED's without a limiting resistor. I was only interested in checking coverage at that point. I stuck in a second one like that and the coverage is fair, not as even as I would like, but good enough for my own use. I will use a 100 ohm limiting resistor when I make the perminent ones up. Quite frankly I would suggest buying the ready made ones for most people, but why write about that on DIY?

With what I have figured out if I was going to do it again I would try to find some 10mm unltra-wideangle high-output yellow LED's and use one each with a 220 ohm resistor.

Now if I if I could do something about the dead LED dial pointer, but that is for another thread.
 
Ah, I made up 7 lamps today. Used a bit of 3/8 water feed for the base, 24ga speaker zip cord for the pigtails. Roughed up the LED's for defusion. There was no room in the base for the resistors so they will be at the terminal strip in the receiver. Hopefully this will all work OK. Didn't think to take photos. But they are basically as I described above a pair of LED's at 15-20 degree angle to each other. I marked the boots so I can tell approximately how they are aligned. Guess I may finish up tomorrow. Be interesting to see just how good, or bad, they look when finished.
 
graywolf said:
Now if I if I could do something about the dead LED dial pointer, but that is for another thread.
Click to expand...
Take a look here:
http://www.audiokarma.org/forums/showpost.php?p=2216476&postcount=8
I put a blue SMD LED in the pointer of my SX-1010. You need to find the brightest one you can for this.
I'm not sure if the above link will work so I reposted the picture below. The SMD LED is quite small so soldering the wires will be a challenge. (I think the "crap" on the ends of the leads is either melted insulation or some glue; I don't remember.) Then I just glued the LED in place of the original pointer bulb (with a series resistor of course). To determine the value of the series resistor I check the current (MA) specs of the LED and then insert a resistor decade box (you could use a potentiometer) along with a digital meter. I adjust the resistance until I get a value that is 75% of the rated current. Sometimes I'll go less if it doesn't affect the brightness much. Then I just insert that value fixed resistor in series with the LED. If the voltage is over 5-6 I'll put a zener diode in series as well.
JimB

JimB

attachment.php
 
OK, some experimental data:

Without a resistor my pair of LED's pulls 95ma. With a 100 ohm resistor (measures 98.9 ohms) in series it pulls 8.5ma. The resistor is dropping 0.87 volt. Which gives 6.7v across the two LED's. As mentioned by others in above posts the resistor is pretty much needed as without it the LED is pulling 5 times its rated current.
 
w1jim said:
Take a look here:
http://www.audiokarma.org/forums/showpost.php?p=2216476&postcount=8
I put a blue SMD LED in the pointer of my SX-1010. You need to find the brightest one you can for this.
I'm not sure if the above link will work so I reposted the picture below. The SMD LED is quite small so soldering the wires will be a challenge. (I think the "crap" on the ends of the leads is either melted insulation or some glue; I don't remember.) Then I just glued the LED in place of the original pointer bulb (with a series resistor of course). To determine the value of the series resistor I check the current (MA) specs of the LED and then insert a resistor decade box (you could use a potentiometer) along with a digital meter. I adjust the resistance until I get a value that is 75% of the rated current. Sometimes I'll go less if it doesn't affect the brightness much. Then I just insert that value fixed resistor in series with the LED. If the voltage is over 5-6 I'll put a zener diode in series as well.
JimB

JimB

attachment.php
Click to expand...

Thanks Jim, the KR-4600 already has a LED pointer, but it is not working. I believe it is one of those that only come on when you are in AM or FM mode. It is wired to the tuner PC board. So the problem may not be the LED. Some trouble shooting is in order. But first to wire up all those resistors and see how the dial looks. If the problem is the LED I will try to find one of those SMD (Surface Mount Device, for those who hate having to look up akro's) LED's.

Stopped and checked, there is 22 volts to that pointer. I guess a resistor shorted out somewhere, and I bet the LED is history.
 
More or less done. Does not look bad, not as even as I would like but definately readable:

Dial-Bulbs---h--20090208.jpg


The diodes mounted and insulated with shrink tubing.

Dial-Bulbs---f--20090208.jpg


And a photo of the modified LED with a stock one on the right.

Dial-Bulbs---a--20090207.jpg


I was thinking of ordering some of Don's to try and get stock looking green lignt, but I think these are good enough for my bedroom receiver. What do you guys think?
 
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