need help designing a led bar

[scampo77]

i have a rheostat that is variable from 0-90 ohm. i am wondering if anyone would be willing to help me figure out how to make the LEDs come on as the voltage rises 0-3 ohm is 1 led and at 85-90ohm is all the leds.

im not sure if i should use op-amps for each step or if there is a simpler way.
any help would be appreciated scampo77@gmail.com

[Evil Lurker]

Re: need help designing a led bar

So lemme get this right your looking for an led bar graph driver IC... how many leds are you thinking of driving?

[scampo77]

Re: need help designing a led bar

it doesnt really matter maybe 10? seems like a nice round number

[scampo77]

Re: need help designing a led bar

i have never heard of this before but after a quick google search i came up with a lm3916 although i might need help wiring it but it seems all contained and nice. my question is with a 0-90 ohm rheostat will i have enough range?

[scampo77]

Re: need help designing a led bar

i have all but decided to go with the LM3914 it is inexpensive and it can drive 10 LEDs. it seems simple enough i just dont understand how it is not required to run rersistors to the LEDs. would anyone be able to help me wire this thing if i order it?

[mariushm]

Re: need help designing a led bar

You can make this with a simple Microchip or Atmel micro-controller. The only problem is that you'd need a programmer to put the code into the chip.

To make a led light up, you just have to connect the led with a resistor in series to one of the output pins of the controller, so if you get a 14 pin DIP chip, you can light up about 10 leds easily.

As for the 0-90 ohm, most of these controllers have 8-10 bit analog to digital converter, basically you feed it the potentiometer/rheostat and it gives a value between 0 and 255 (for 8 bit) or 0 and 1023 (for 10 bit versions). So depending on the value the chip determines, you can light up 0 to whatever leds you want.

Here's two videos where the analog to digital converter and the leds lightning are shown with a cheap Atmel microcontroller:


http://www.youtube.com/watch?feature...GzBhx08#t=224s
http://www.youtube.com/watch?v=GSuyn...eature=channel

http://www.youtube.com/watch?feature...&v=e7X6LGXhOss

The programmers for this Atmega are cheap, and there's lots of them ... the official one for Microchip PIC controllers is more expensive but the chip is just as good as the Atmega one.

[Agent24]

Re: need help designing a led bar

LM3914 is probably cheaper and easier to start with though

[budm]

Re: need help designing a led bar

If you download the spec sheet, you will see how the LED curent is being controlled, circuits example, etc.

[scampo77]

Re: need help designing a led bar

if anyone is still following this thread i could sure use a hand i do not understand what pins 6,7,8 do?

i thought if i drove .5v into low ref and 4.5 into high ref then on pin 5 i put a variable signal of .5 -4.5 and one or all of the bulbs should light up?

well with just .5 on pin 4 it gives me voltage on pins 6+7 of about 2v and when i put my ref voltage of 4.5 something that is going on in the IC is dropping it to around 3v.

im very new and very confused as to what is happening or how to fix it. what is adding to the confusion is when i google how to wire this up i get 3 different ways to wire the same IC.

[Agent24]

Re: need help designing a led bar

https://cdn.badcaps-static.com/pdfs/...35bad9b546.pdf

I've not used a LM3914 before but for a first try, give the reference circuit on page 3 a go. Once you have that working, try other stuff.

[scampo77]

Re: need help designing a led bar

i got this working from info online and everyones help, thank you everyone!!

i am having a problem where the bar graph jumps and moves in real time i need to slow it down. i need to add a cap but i dont know where to put it. i am assuming my .5-4.5v on pin 5 needs a cap but do i put the neg cap lead to ground and pos to pin 5? or do i just put it inline to pin 5? i think there is a resistor involved?

how big of a cap do i need to use?

i thought i would start withg a 47uF 25v but i dont know where to put it.

[Uranium-235]

Re: need help designing a led bar

make sure the place is packed with tons of music and bitches. LED's love bar bitches

[Agent24]

Re: need help designing a led bar

i got this working from info online and everyones help, thank you everyone!!

i am having a problem where the bar graph jumps and moves in real time i need to slow it down. i need to add a cap but i dont know where to put it. i am assuming my .5-4.5v on pin 5 needs a cap but do i put the neg cap lead to ground and pos to pin 5? or do i just put it inline to pin 5? i think there is a resistor involved?

how big of a cap do i need to use?

i thought i would start withg a 47uF 25v but i dont know where to put it.

In series won't work because it will just block the current, and you'd get nothing.

Across pin 5 to ground sounds like it makes more sense (assuming that pin is normally in respect to ground)

[scampo77]

Re: need help designing a led bar

I tried that and it didn't work I even tried different sized caps up to 6800 uF. Is there a name for this type of circuit? Is this damping?

[cadiman]

Re: need help designing a led bar

If you can find an old Radioshack booklet on led bar graph. You can build one with an op-amp circuits.
I made one about 30 years ago. It was a bar graph volt meter and you could change the gain and use it for audio. I am sure I did.

It used 339 or 741 op amps one for each led and a 100k resister you could adjust for gain pending input source.

I am sure I still have the books in my file.

They were called Engineer`s Mini Notebooks and lots of cool circuits using op-amps,555 timers and other semiconductors.

[budm]

Re: need help designing a led bar

Is there any reason why the diagrams by ben and mine and any related questions removed?

[cadiman]

Re: need help designing a led bar

Not sure, but I like Uranium-235 post!

[ben7]

Re: need help designing a led bar

Is there any reason why the diagrams by ben and mine and any related questions removed?

Hm, Im not sure, I just realized that they were missing!

EDIT: lol, all my posts had gotten deleted too.

[budm]

Re: need help designing a led bar

I forgot that he started the new thread:
https://www.badcaps.net/forum/showth...394#post251394

[ben7]

Re: need help designing a led bar

I forgot that he started the new thread:
https://www.badcaps.net/forum/showth...394#post251394

He doesn't seem to be interested in that project now