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By: xDGx (offline) on Wednesday, April 07 2010 @ 10:53 AM PDT (Read 3706 times)  
xDGx

I've got a question:
I've build a VU meter using a 10 LED bar graph and a LM3914 on my small breadboard. It's nice and dandy, but it's too small. I'd like to make the same VU with 100, 200, 300 LEDs (or more!) instead of only 10. I want to put it on my bedroom wall :-)

I could just leave the question as is, but I've made some research and came up with - obviously - even more questions... Rolling Eyes

* Some people say the LM3914 is not suitable for the task (it *DID WORK* perfectly with 10 LEDs). TRUE or FALSE ?
* Cascading LM3914 would't make it work right (even though I've read cascading is possible on the IC datasheet; didn't test it because 1) I only have 1 IC so far 2) Didn't really want to spend more if it's gonna be useless). TRUE or FALSE ?
* I'd have to use a solid state relay to light a bunch of LEDs to keep the visual effect. TRUE or FALSE ?

I have a MAX7219 and some Peggy 2 spare parts including ICs... maybe they'll be useful for this ? I don't know. I'm pretty happy I made the VU with 10 LEDs, but extending it to 100 is tricky (the assembling part of things). Didn't find any decent tutorial online..

That's also a nice (and huge) Evil Mad Science project suggestion !


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By: Windell (offline) on Wednesday, April 07 2010 @ 08:37 PM PDT  
Windell

>I'd like to make the same VU with 100, 200, 300 LEDs (or more!) instead of only 10.

It looks like the LM3914 is designed to do that exactly, with at least up to 100.

In a quick examination, it's not clear to me what-- if anything --limits it, so you may be able to go right up to 300, with some degradation in fidelity, linearity, and noise.

>* Some people say the LM3914 is not suitable for the task
>(it *DID WORK* perfectly with 10 LEDs). TRUE or FALSE ?

I don't know. It seems perfectly plausible that some people would say that it isn't suitable; I haven't read that opinion, though.

>* Cascading LM3914 would't make it work right (even though I've read cascading
> is possible on the IC datasheet; didn't test it because 1) I only have 1 IC so far 2)
> Didn't really want to spend more if it's gonna be useless). TRUE or FALSE ?

I'm not sure what you're saying or asking here-- why wouldn't cascading work for you? My impression is that you wanted to do exactly what it says on the datasheet.

>* I'd have to use a solid state relay to light a bunch of LEDs to
>keep the visual effect. TRUE or FALSE ?

That's a false-- I'm not sure what you're trying to do, but I'm pretty sure I don't see a need for solid-state relays anywhere.


> have a MAX7219 and some Peggy 2 spare parts including ICs...

If you wanted to build this digitally instead of analog, you could use the LED drivers from the Peggy (STP16DP05B1R or equivalent) to drive up to 16 LEDs at a time each. Two of them can drive 32, and so on. Should be easy to get to 300 LEDs that way.


Windell H. Oskay
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By: xDGx (offline) on Tuesday, May 11 2010 @ 01:55 PM PDT  
xDGx

Good news I've been trying to make this work and got some positive results, both on a breadboard and with a little homemade PCB that I bought ( never made a PCB at home ). Both with 10 LEDs, no cascading yet.

Bad news using a breadboard is a little frustrating with all the wires and bad connections that comes from it, making troubleshooting a tedious process. I didn't even try cascading on the breadboard yet as I have to hold wires myself to watch it working. The PCB is better, but too small.

After a lot of searching I didn't find a board using multiple 3915 or 3914 which makes me think I'm the only one doing it (I doubt it) and there're no PCBs out there to build this as a kit (not sure).

I'm on a dead end here. I can try to make the schematics myself on Eagle and then build the board myself, which I guess is going to be a little hard to do because I don't know to use Eagle app and never produced a board at home.

This is just an update, no real questions here. Thought I should share. Any tips for this journey is appreciated Smile
Best,


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