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Need help with very basic task(atleast i hope)

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Hey ok the layout is being made, but to give you a heads up it is exactly like their table in the video. the VU meter will be in the same place and will look exactly the same as that. We will only have the vu meters. I was thinking about the wiring and how you said each channel on the IC will drive 8 LEDs. There are 20 Leds per strip and since 1 IC does 10 leds i will daisy chain two to handle the 20 channels. Here is where i am going with this. The first channel deals with the first set of LEDs. So will those 8 Leds have to be run on the same wire? Im not sure if i am explaining this right.
 
Hey ok the layout is being made, but to give you a heads up it is exactly like their table in the video. the VU meter will be in the same place and will look exactly the same as that. We will only have the vu meters. I was thinking about the wiring and how you said each channel on the IC will drive 8 LEDs. There are 20 Leds per strip and since 1 IC does 10 leds i will daisy chain two to handle the 20 channels. Here is where i am going with this. The first channel deals with the first set of LEDs. So will those 8 Leds have to be run on the same wire? Im not sure if i am explaining this right.

Hi there!

Sorry for the late response. I'm not ignoring you, I'm just busy these days. :)

Anyway, if I understand your meaning, then yes, the LEDs in each channel's chain will need to be in series--"on the same wire".

Here is a quick (OK, so not so quick--doing anything repetitive in Eagle is like kicking a dead whale down the beach) diagram showing how I'd hook it up for one LM3915. The LEDs are arranged into 4 groups of 20, essentially how they'd be laid out on the table. For 2 LM3915s you'd just do this twice.

large_vu_meter_1-png.22635


Note that there are no current limiting resistors to the bases of the PNP transistors. This is because the outputs of the LM3915 are current-controlled--it would try to compensate for the resistors anyway so as far as I know, they would be superfluous. The datasheet shows how to program the outputs' currents so I'd try to use that to set an appropriate drive current to put the PNPs into saturation. (I've never used an LM3915 so this might be wrong--I hope someone with more experience in this will correct me if I'm leading you astray here).

I'm also being just a hair conservative with the LED current-limiting resistors, but I think you should use 1/2 Watt resistors for the LEDs.

Make sense?


Torben
 

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Hey that looks awesome. I will take it to one of my professors and see what he thinks. Sorry I havn't been on the forum lately. I had a couple test this week and fraternity stuff. But i think the LEDs should come in today and i will post an update aswell.
 
Hey that looks awesome. I will take it to one of my professors and see what he thinks. Sorry I havn't been on the forum lately. I had a couple test this week and fraternity stuff. But i think the LEDs should come in today and i will post an update aswell.

Cool. Maybe start with a 1mA load on the Reference pin to program the outputs.

Make sure to provide the professor with an LM3915 datasheet. :)


Torben
 
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