make this VU meter more sensitive, please

[Pharaday]

hey guys here's this VU meter that I pulled off of an inverter battery combo, I'd like it to run off of the input from a little amp so anywhere between 2 and 10 volts should excite it. I can do that by changing out some of these resistors for a lower value, right? could you show me which ones? I can't seem to find a circuit diagram for a VU meter using this chip. it's a μPA2003C.

 

[bertus]

Hello,

The μPA2003 is likely an ULN2003 darlington array.
The resistors are choosen to have enough current to light a led through the ULN2003.

Bertus

 

[Harald Kapp]

The µpA2003C is simply a driver array (datasheet). It looks like the "tresholds" are set using the intrinsic "threshold" of the transistors plus series resistors. This is a rather crude device, I guess it was meant to monitor some internal voltage for a comparatively coarse indication of voltage level.
It will probably not work down to the voltage levels you envision. Even if it does, the brightness of the LEDs will vary considerably as there is no controlled current source but only series resistors.

I recommend you put this board into your parts bin and get a decent module based on the venerable LM3914 bar graph IC.

 

[Pharaday]

somebody gave me a tool box made out of plastic but inside of it was an inverter and a battery and the little plugs for connecting a solar panel. It had a button that when pressed, that circuit would indicate battery charge level but I it didn't need that and I wanted the button for something else. I'm guessing the battery was 24v or higher cuz a 12 volt battery barely lights it up. I got a few chips out of stereos that do this better but I was hoping to make this part useful beyond the LEDs and resistors but if I can't, I can't. Preesh!

 

[bertus]

Hello,

The LM3914 that @Harald Kapp mentioned has a linear scale.
The LM3915 has a scale in 3 dB steps.
The LM3916 has a scale like a VU meter.

Bertus

 

[Pharaday]

I have not harvested any of those chips yet. I'm getting around to building one out of just zeners and transistors etc but just as the old saying goes, I haven't done it yet.

 

[bertus]

Hello,

If you are looking for some led vu meter schematic, just google:
led vu meter schematic
Many use the mentioned chips, but some use a diode array or a couple of LM324´s

Bertus

 

[Pharaday]

yea there are few designs out there that don't use any chips at all just zener diodes and transistors and resistors. I have 2 circuit diagram just like that in my documents waiting for me to find all the zener diodes out of my electronic component storage facility AKA a closet full of circuit boards.

 

[Pharaday]

I have money but I still get solder by torching the backside of the circuit board and banging it on a table and then gathering the little droplets. the older the circuit board the better. these SURFACE MOUNT circuit components are screwing me over in so many ways

 

[Audioguru]

The LM3914 is a linear voltmeter indicator IC not used for audio.
The LM3915 3dB per steps audio level indicator IC is obsolete. I guess I bought the last few that were made.
The LM3916 many levels audio IC is made by a copy-cat company and costs a fortune.

 

[bertus]

Hello,

One could mimmick the LM chips with the internal schematics, using a couple of LM324´s.



Bertus