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led vu meter. simple question

R

Randolf

Limp Gawd
Joined
Jun 12, 2003
Messages
149
alright. I have a LM3914 from a past led project. I forget what I used it for since what ever it was supposed to do it didnt do. any how. looking at the data sheet shows that it works between 6.5v and 18v. I'm wanting to use a bunch of surface mount blue leds that I have laying around.

is the lm3914 gonna cut it for the vu meter. or should I get something else. and if so what should I get? I've got the basic schematic scratched out and the diffrent chips would be easy to drop in. I'm just wondering about resistor or a power circuit.
 
now i remember why I have this chip. already built one for a old case tha I scraped long ago. the circuit has been sittng in my projects box for a few years now.
 
The LM3916 would actually be better for a vu meter since it uses a logarithmic scale, whereas the LM3914 uses a linear scale. The LM3914 would still work, but you won't see much activity until your source gets really loud. Or maybe you'll get a lot when it is soft but then once it is louder it doesn't change much. I can't remember which way it is. Anyway, LM3916s are better for vu meters.
 
would I need to place a resistor on each pin since the documentation shows a max of 5v coming off?
Click to expand...

Nope, just use a single resistor between the V+ rail and the LEDs.
(this also helps keep the LM3914 from sinking to much current)
 
Mister X said:
Nope, just use a single resistor between the V+ rail and the LEDs.
(this also helps keep the LM3914 from sinking to much current)
Click to expand...


cool. thanks. got something for me to do before work friday night,

jpmkm said:
The LM3916 would actually be better for a vu meter since it uses a logarithmic scale, whereas the LM3914 uses a linear scale. The LM3914 would still work, but you won't see much activity until your source gets really loud. Or maybe you'll get a lot when it is soft but then once it is louder it doesn't change much. I can't remember which way it is. Anyway, LM3916s are better for vu meters.
Click to expand...

I'll use a socket for the chip. that way I can just drop in the lm3916 if the lm3914 doesnt work as planned
 
Randolf said:
cool. thanks. got something for me to do before work friday night,



I'll use a socket for the chip. that way I can just drop in the lm3916 if the lm3914 doesnt work as planned
Click to expand...
Yes, I'm pretty sure the two chips are pin-compatible, but you'd have to check the datasheets to verify that.
 
yeah. bough a strip of 20 smt leds for a cell phone mod that never took place and I'm working on a plexi htpc. it has a bit of empty space near the back for the circuits.

I'm going to etch a grove into a peice of plexi then mount the lights on it.put it all behind frosted plexi glass you will never see it till it lights up. I'm figuring two 10 led graphs on each side of the case. the lights arent to bright so it wont be annoying. and i'll add a switch to turn them off if I dont want them.
 
Good idea with the switch, cause I don't think it's possible for them to not get annoying. :D

I would also Add a switch to select between bar and dot mode as well cause I found that was kinda cool. ;)

I got a very simplified schematic around here somwhere if you need it.....
 
The datasheet also has some simple circuits that might be useful.
 
4330vumeter.png


This is a little easier then the stuff in the datasheet cause you simply change the value of the unlabled resistor to adjust the brightness of the leds. :)

The 1uF input capacitor and the pot are optional... so is the mode switch.
 
hmmm/ I think I did something wrong. I dont think the chip is supposed to get hot :eek: only 9v input too... guess I'll take it apart tonight and check the wiring.
 
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