Need instrutions on LED moding Casio TV-880

Hokusai · Post by **Hokusai** » Fri Dec 30, 2005 8:15 pm

I have looked, and all I found were the 680, 890, and so on here so I decided to post about it. Sorry for the lousy pics but all I have is a webcam.

I have two nice, not too bright white LED's ready to go. Also if I can do so without breaking it, I plan on cuting the light tube end to put my LED's in.

G-force · Post by **G-force** » Fri Dec 30, 2005 10:15 pm

Wouldn't it just be the same as any other pocket TV? Just take out the lamp, stick LED's in each end of the lamp holder, and power them with the correct resistor.

Hokusai · Post by **Hokusai** » Fri Dec 30, 2005 10:33 pm

Well it may be... This is quite the shady area for me though. But isn't there suposed to be some way to remove I guess it's a transformer? Then put the LEDs in the same spot as where the transformer was at?

Kurt_ · Post by **Kurt_** » Fri Dec 30, 2005 10:36 pm

I was thinking about something....didn't want to start a new post about it though.

I noticed that the brightness buttons on the actual LCD didn't make much difference (If any) after I did the LED mod.

A variable resistor would work, right? Like a potentiometer?

That would be cool. If it's bright out you wouldn't need to have it any brighter than you needed (although you'd still probably need the same amount regardless)

@ Hokusai

I'm assuming you know how to put the LED's inside the LCD backlight compartment.

1) Use a multimeter and find 5v (on a regulator, usually)
2) Hook up a resistor (about 10-30 ohms, it really depends on how bright you want it)
3) Attack the resistor to the 5v, then attach the other end of the resistor to the longer (positive) end of each LED.
4) Attach each negative end to each other, and attach it to a ground.

Hokusai · Post by **Hokusai** » Fri Dec 30, 2005 10:47 pm

Ah I get it now, just have to have the batteries in it while working on it..tszzzz lol

Since my LEDs are rated to 3.5v I'm going to add resisters to bring that 5v down to 3.4v. Should be safe runing at that yea?

Kurt_ · Post by **Kurt_** » Sat Dec 31, 2005 10:32 am

I don't believe that would do ANYTHING.

I think resistors slow down the CURRENT. ie. amps, not voltage.

You shouldn't work on it with the batteries in. That's just insane.

Get a multimeter and find a spot where 3.4v comes out of then.

And are you sure your tv will run off 3.4v? I'd think you'd need 5?

(If you don't know how to use a multimeter, you really need Ben's book. To be honest I didn't really have that much of a clue either, I knew what everything meant but had no clue how to use it, because nobody ever taught me, since I've never had to know. Ben's book taught me in less than a minute.)

Xaxle · Post by **Xaxle** » Sat Dec 31, 2005 11:08 am

I think resistors slow down the CURRENT. ie. amps, not voltage.

Resistors change the voltage, remember:

V = IR
(Ohm's Law)

So the higher the resistance, the higher the voltage "used up" on that resistor, so the less voltage left for the rest of the circuit.

Kurt_ · Post by **Kurt_** » Sat Dec 31, 2005 11:15 am

RESISTOR - A two-terminal electronic component that resists an electrical current and turns the extra current into heat. Resistors are rated in ohms, and can be used to regulate the voltage and current in a circuit. Basically, a resistor resists the flow of electricity. Resistors are used to lower voltages and currents so that components that require smaller voltage/current can function properly. If a power supply puts out 12 volts and you have a chip that runs on three, you need a resistor to cut down the voltage.

I think a resistor does both, actually...but I wouldn't doubt it if I was wrong.

Xaxle · Post by **Xaxle** » Sat Dec 31, 2005 11:26 am

This is a huge tangent but:

The current stays constant throughout a circuit, what goes in comes out. The voltage is "used up" by the circuit, to that whatever voltage comes in, it goes out as 0. In a series circuit (which I'm assuming this particular instance is, as putting the resistor in parallel with the white LED would do absolutely nothing to help the voltage), the voltage is shared out among the components depending on the resistance of each component. The white LEDs will also have resistance. So by putting a resistor in the circuit, some of the voltage is "used up" by the resistor, and the white LEDs end up with less voltage than they would have without the resistor.

I think that explains it correctly in basic terms....

To Hokusai:

I would think that bringing the voltage through the LEDs down to 3.4v should be fine, try it out and see.

Post by **Gamelver** » Sat Dec 31, 2005 12:30 pm

here's a quick circuit diagram to show how the resistor works (way off topic, but I thought I'd share this

):

ok, so first you have the 5V source. the voltages at the resistor and the LED must add up to 5V. since you know the LED is at 3.4V, you know the resistor voltage is 1.6. If the current flowing through the LED is 20mA, then you also know the current flowing through the resistor. Since you now have I and V of the resistor, use Ohm's law to get the resistor value. From this you can set up the equation to get the resistor vaule: R=(Vs-Vf)/I where Vs is the supply voltage, Vf is the LED voltage, and I is the LED's current rating.

so if you've got one LED rated for 20mA at 3.4V, then you'll need an 80 ohm resistor if you're using a 5V source.

make sense

?

Hokusai · Post by **Hokusai** » Sat Dec 31, 2005 1:29 pm

Yea it does. Just going to be hard to find the proper resistor for what I need though. (tearing apart junk electronics for what I need) Wich leads me to belive that my LEDs are capable of higher voltages. Just conected them to 4.5v and they woked fine. Also they came out of an old walmart brand bike headlight made by bell. Though I think it has 6v runing to two LEDs.

Post by **Gamelver** » Sat Dec 31, 2005 1:53 pm

well, diodes have set voltages....if you input 5V, then they'll still be at 3.4V or whatever they're rated for. input too much voltage, though, and I think the current becomes too much and they literally fry (I've done it before

).