Ultra TV-B-Gone

Step 4: Make the LED Array

Start with two LED's and decide which direction you will stitch. Bend the inside lead towards the second LED and solder it then repeat until you have a string of four LED's. Then repeat the entire process five times.

Now bend the leads of one set to the side and attach another set between the two bent leads. Repeat this until you have filled out the entire grid.

Note: Always check the polarity of the LED's you are soldering. This configuration creates five parallel blocks of four LED's in series.

Comments

[ksikes]

Do you think its possible to build your own TV?

[bears0]

someone said their dad made one. don't remember who, but it would not be a project for people with limited supplies equipment or tools.

[rocketbat]

i currently have about 100 ir LEDs i was wondering, since it is in parralell would twenty five rows of four work? (evil laughs!)

[tod123]

Yes but you would need a bigger transistor, and i dont know if a 9v battery can supply this kind of current

[geeklord]

you did a pretty good job soldering those

[Wired_24_7]

using a shotgun as a sniper rifle. I like it.

[kiwisaft]

LEDs in parallel is no good - they never get exactly the same current each. one might get some more current, maybe too much -> it'll die, and in chain reaction the others will die, too

[thinkdunson]

no it won't. all branches always get the same amount of current (ignoring manufacturing imperfections). besides, even if they did get more current, it wouldn't damage them (see my reply to servant74).

[servant74]

Yea, it isn't the best electronic design. Given that most that do build it won't have a multi-year device, I still think this is a great hack. Normally, putting a resistor at the end of each 'string' of LEDs to keep the current in check is the 'right' way, then you can run the 'strings' in parallel. That way if one 'string' dies, it all won't come tumbling down.

[thinkdunson]

the design eliminates the need for a limiting resistor by putting groups of four LEDs in series. these groups are then connected in parallel. connecting the LEDs in series effectively adds their resistance in series with the other three LEDs in that group. so in effect, they do have the protection of a limiting resistor.

[kiwisaft]

this will work, but it's not true. except you use an high accurate voltage supply ;) 1mV more or less for a diode will cause many mA more or less current. that is what diodes for and LEDs are diodes

[thinkdunson]

i'm sorry, but this post makes absolutely no sense.
first of all: "this will work, but it's not true." what does that mean?
second, i have no idea what you are trying to say diodes are for, so i'll tell you. they are mainly used to allow current in one direction and not the other.
as for the 1mV thing, i'm not sure what you're trying to say here either. but i am aware that diodes follow ohm's law.

infrared LEDs typically have at least 1.2V required to forward bias. so by putting four of them in series: 1.2 x 4 = 4.8V your voltage drop is around 4.8V. a 9volt battery minus 4.8V = 4.2V. so the LEDs are seeing 4.2V each.
i've measured the internal resistance of two IR LEDs. one had 81ohms, the other had 82ohms. lets even play it safe and say they are only 50 ohms each. 4.2V going in to four 50ohm LEDs in series = 21mA. that's low enough right there. but when you consider that they were closer to 80ohms, you get only 13mA.

in short, you are in absolutely no danger of melting an LED if you follow the instructions that m_jake gives for this project.

as a side note, IR LEDs have the lowest internal resistance. as you move up in hertz, you get higher forward bias, and higher internal resistance. so blue LEDs are the highest. (i've never seen a purple LED.)

have fun

[Electronics Blurred]

i have bought a few purple and pink LED's . red seems to be the strongest current hungry roundup of LED ( i'm refering to those transparents glass on top ones ) Purple seems to be on par with Green , Red & blue two colour LED's aren't really current hungry , but it is power hungry when it switches colours ( as my name implies , i'm really not having much knowledge about diodes , etc. ) that's all i know ( I'm a grade 10 singaporean )

[thinkdunson]

p.s.
when i say internal resistance i'm including effective resistance as a result of voltage drop. i found it by connecting them to a 4.94V source in series with a 219ohm resistor. current was 16.44mA and 16.41mA.

4.94V / 16.44mA = 300.5ohms.
300.5ohms - 219ohms = 81.5ohms

[kiwisaft]

I tried to say, that the diode-resistance is not linear. so you can NOT use Ohm's law for them you can't say "50ohm LED"

[kiwisaft]

there it is

[thinkdunson]

i measured my LEDs at 4.94V. so the 4.2 or so that these see will cause them to have an even higher resistance than i measured. meaning they will have to sink less current. all the better.

[network24]

do u strip da wires after u solder dem or something

[MadMechanicMike]

what are you talking about

[aiden120000]

What would I have to do to use white LEDs, and make a torch type thing out of this array?

[mitch]

If you want to build a torch (i.e., "flashlight" in Americanese), I believe all you need to do is build the 20-LED array out of white-light LEDs, and simply connect it to a 9 volt battery.

[technosapien]

You may need to include a resistor if you do that, check the voltage drop across the white LEDs or do a google search for LED Resistor Calculator and you will find some sites that can help you figure out what you need. I connected two superbright LEDs to a 9V battery and it worked well, I did need a small resistor though to prevent overload on the LEDs.

[aiden120000]

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