I'm kinda Bamboozled at this...

G-force · Post by **G-force** » Mon Feb 27, 2006 5:14 pm

See I'm gonna try an LED mod on my Psone screen, since it can't seem to run correctly while an N64 is running off the same power supply. The voltage on the battery drops from 7.4V to 6.4V when I turn the system on, and the screen barely runs. The N64 runs fine (had the video hooked up to a TV for comparison), but the screen is very distorted. I even tried adding another AA cell to make 8.4V, it still dropped a whole volt to something like 7.4V and the distortion was still there! It's odd since the batterys are rated at 2700 mah and it seems like a screen and N64 wouldn't pull that much!
I figured an LED mod was worth a try, I mean whats the worst that could happen, I end up with more battery life!

Anyways, I was reading bens guide on how to do the mod on extremetech and I noticed it called for a 10 ohm resistor for the LED's in parralel off the 5V regulator. I was using the same LED's as in the guide so there really was no reason for me to check the resistor value. But I did anyways using metku's calculator (I could't remember the equation so I took the easy way out.).
The answer I got was a 22 ohm resistor instead of a 10 ohm...

Here is the data I used for the LED calculator, my LED's are from www.digi-key.com part# CMD204UWC-ND.Here's the PDF.

(using metku's parallel LED calculator)
Supply Voltage: 5V
Voltage Drop Across LED: 3.7V (this I wasn't sure about, I assumed it mean the normal LED voltage.)
Desired LED Current: 20 mah
How many leds connected: 3

And it said 21.667 ohms (22 ohms). So either I made a mistake or the LED's have changed, or Ben made a mistake (not likely). So is it a 10 ohm or a 22 ohm?

Sword_Gun · Post by **Sword_Gun** » Mon Feb 27, 2006 5:33 pm

Sorry to go off topic my kind friend, but what is a LED mod?

G-force · Post by **G-force** » Mon Feb 27, 2006 5:37 pm

It's a power saving mod where you replace the CCFL (I think...) backlight with white LED's. It has a few up and downs, but I think I need it for this project.

Sword_Gun · Post by **Sword_Gun** » Mon Feb 27, 2006 5:39 pm

Oh, I understand.
About your question, I not really sure, but thank you kind sir.

daguuy · Post by **daguuy** » Mon Feb 27, 2006 6:18 pm

10 ohms would probably work but just be brighter. my LEDs came with resistors and they work fine with those. i was bored and wired 2 parrallel but one had the resistor it came with and one a had a pot i got from some junk. i turn the pot to see how bright the LED could get before it burned out and it got a lot brighter than the resistored LED. it only changed color (that's how you tell when the resistance is too low) when i turned the pot to nearly no resistance. the suggested resistor is higher resistance than you need but would work. use 10 ohm if you want it to be brighter

riva16 · Post by **riva16** » Tue Feb 28, 2006 3:01 pm

Ohh man, that was funny... Quote: "I mean, whats the worse that can happen? Longer battery life!

" UHH! "What's the worse that can happen?" You can break your $50 LCD screen! Come on... Throw a resistor int here first! God d*mn!

Post by **Gamelver** » Tue Feb 28, 2006 3:06 pm

you can't break the screen, unless you rip off the CCFL inverter first, before doing the mod. you might fry the LEDs without a resistor, but not the screen

.

and let's see....(5V-3.7V)/.060=22 ohms

yup, use a 22ohm resistor. anything lower might get a little brighter, but the LED would decrease a lot.

G-force · Post by **G-force** » Tue Feb 28, 2006 3:32 pm

Thanks for confirming that. I wonder why ben would say to overdrive the LED's

Anyways, I completed the mod. With the 22 ohm you couldn't see anything. It was actually that weak. So I switched to the 10 ohm. Brighter, but still too weak. Everything looked very washed out and dark, turning up the contrast made no difference only washed the image out more.

I followed bens guide to the letter, and I have to say, it sucks. The colors are washed out, the lighting is uneven (especially in the corners). even brighter LED's wouldn't help, the screen just looks plain looks bad with LED's,

I'm switching back to the CCFL and inverter, which I was very careful to not destroy. It's MUCH better than this. What a waste of time though...

(BTW, the mod didn't help my problem at all, even after desoldering the CCFL inverter it made no difference.)

Post by **Gamelver** » Tue Feb 28, 2006 3:44 pm

well, it looks all right with my aluminum trick

. sorry to hear that it didn't fix your problem, though

.

Trv · Post by **Trv** » Tue Feb 28, 2006 4:12 pm

Gamelver wrote:well, it looks all right with my aluminum trick . sorry to hear that it didn't fix your problem, though .

I did that and it looks as good as the backlight. I also reccomend using 4 leds to spread the light even more

daguuy · Post by **daguuy** » Tue Feb 28, 2006 4:28 pm

i used 6 with the brightness mod and alumium foil and it looks as good as the ccfl tube. did you do the brightness mod? you absolutly need to do it for the screen to be usable

akadewboy · Post by **akadewboy** » Tue Feb 28, 2006 5:15 pm

I've heard that white is actually a better reflector than aluminum foil. Has anyone ever tried using something white to reflect the light?

daguuy · Post by **daguuy** » Tue Feb 28, 2006 5:44 pm

the back of the light box is white. the problem with it is that it isn't opaque so aluminum foil makes the light go through the LCD and not out the back

Post by **marshallh** » Tue Feb 28, 2006 6:01 pm

You must not be doing the LED mod right, I did it and it works great - almost as good as the CCFL.
There's probably not much difference at all between the 10 and 22 ohm resistors - they wouldn't make that much of a difference.

G-force - I think you problem here is you're just flat out pulling too much juice from the AA cells. They're just not made to handle a 2amp+ discharge rate... only for stuff like digital cameras. RC car batteries on the other hand are made to discharge at up to 20 amps.

I had the same exact problem as yours when I ran the TI regulator and my N64 off 10 AA batteries - the batteries got quite hot and the voltage sagged.
Time for bigger batteries.

akadewboy · Post by **akadewboy** » Tue Feb 28, 2006 6:01 pm

I see now, thanks for clearing it up. I've only messed with Hip Gear Screens so I wasn't sure how a PSone screen was physically configured.