Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

30 Leds VUmeter 1dB step.

Status
Not open for further replies.

vmsa

New Member
I have an idea about to build a bargraph vumeter with a 1dB step, with a range of 30dB, then I need 30 Leds. I think to use the LM3915, but it is 3dB/step.
Anybody know a way to build this meter?
The response time may be average. The scale I need is about -23 to +6dB.
Any ideas welcome.
Thanks.
Victor
 
A microcontroller can be programmed to perform the function of the 3915, with the advantage that you can select the step size. Elektor Electronics Magazine – 07/2005 has a 12-LED VU meter that you can use as an example (article is for sale) for $6. **broken link removed**
 
Thanks mneary, but this design is not exactly I am looking for. It has only 12 leds, it is linear, need a programmable device (Attiny15L microcontroller), use a complicated charlieplexing output and is for low current leds. I would like a more simple design. There are one?
 
If you want 30 1dB steps, then use three LM3915's - the datasheet shows how to connect them in series.

As suggested, you could easily do it with a processor - I did a stereo 16 LED's per channel one, switchable lin/log and dot/bar - like a super stereo LM3915/6, using a PIC 16F876. You could easily make it 30 LED's.

But if you don't do PIC programming, then stick to the LM3915's.
 
The steps on an LM3915 are 3dB apart, not 1dB. One LM3915 shows a range of 30dB.
Most people cannot hear a small change of level of only 1dB in music. 3dB is not much of a change.
 
The steps on an LM3915 are 3dB apart, not 1dB.

The changes are 3dB at the specified signal levels, just stick an amplifier in front to make it read 1dB steps instead - although I quite agree that 1dB steps are pretty pointless. According to the datasheet you can use a maximum of three of them to give a 90dB range at the specified levels.
 
You must use an expander circuit to reduce the 3dB steps of an LM3915 to only 1dB.
 
Thanks boys for your support !!!
Nigel, as you said, if the steps are 3dB, I could change it to 1 dB with a 20 dB amplifier (10 times) in the input. Is this correct?
Audioguru, the problem (my need) is not if you hear or not the change, is the resolution of the display. Anyway thanks for the point.
Nigel, have you a diagram about your design to see how it is implemented with a microprocessor?
I saw some designs with a LM3914 and a logaritmic amplifier in the input.
But I think, why it is needed, if I have a logaritmic LM3915 as choice?
 
Each step of an LM3915 is 1.414 times (+3dB) higher than the last one. One dB is only about 1.1 times higher than the last one.
Adding gain has nothing to do with decreasing the ratio between the steps.
 
Nigel, have you a diagram about your design to see how it is implemented with a microprocessor?

Unfortunately not, nor do I have the software - it was seven years ago I built it - hardware wise it's simple enough, I used two analogue inputs for left and right (after rectifying the audio), and multiplexed two rows of 16 LED's using 17 pins.

For the display I used two lookup tables, one linear and one log (generated using a Delphi program), and selected the correct table based on the setting of an I/O pin.
 
The project that I posted shows how to implement it with a microprocessor. If you don't like charliplexing you don't have to do it that way, it just takes a few more pins.
 
Apparently my idea about to build a simple 1dB bargraph is not easy in the analog world. May be done using discrete comparators, but not with the LM3915. I will try with some desings.
Thanks for your support.
 
Apparently my idea about to build a simple 1dB bargraph is not easy in the analog world. May be done using discrete comparators, but not with the LM3915. I will try with some desings.
Thanks for your support.

As AG has mentioned, why do you want 1dB?, it's really completely pointless.
 
Good point, as you sure know, the major Vumeters in the professional market have a 1dB step. Then I want to have a professional look device. Also the resolution given by a 3dB display is not enough to edit or control audio material. I personally prefer a needle vumeter than a leds one with a 3 dB step.
 
Last edited:
Hi!,
Finally I found a solution, simply with a matrix using three LM3915 (in bar mode) interleaved , I used a 1dB increase in each reference voltage, this gave me 1dB/step and a 30dB meter, as I wanted. Is simple, cheap and it's working perfect. YES, I did it !!!!
 
I did not notice this thread the first time around.

Although you now have a working solution, I am going to suggest that an AD8307 logarithmic detector which gives a DC output which is linear to the dB level of the input could be used with three cascaded LM3914s to achieve the desired result.

If anyone wants to follow up on this idea, be my guest.

JimB
 
Almost nobody can hear the very small 1dB change in the level of music or voice. But most people notice a small change in level with 3dB.
Then why use a 1dB resolution on a VU meter?
 
Almost nobody can hear the very small 1dB change in the level of music or voice. But most people notice a small change in level with 3dB.
Then why use a 1dB resolution on a VU meter?
I also wanted more accuracy in normalizing my MP3 files that I use to make CDs. The design I use has steps of about 1 - 1.4dB in the vicinity of the -3 to +5dB range of the meter.

As it turns out, the LED meters are terrible at giving accurate loudness levels, ie how loud it's going to sound on playback. It's because they register peaks but many audio files use compression or clipping so the peaks may be much lower with respect to average level on different files.

I went back and added the analog VU meter which is very accurate for displaying "loudness" to the ear. The LED meter is basically just pretty lights.
 

Attachments

  • AN-DIG-NUE.PDF
    32.8 KB · Views: 387
@vmsa
A neat solution. Good to hear you got it working!
 
Hi!,
Finally I found a solution, simply with a matrix using three LM3915 (in bar mode) interleaved , I used a 1dB increase in each reference voltage, this gave me 1dB/step and a 30dB meter, as I wanted. Is simple, cheap and it's working perfect. YES, I did it !!!!

VMSA Got a question.
You moved the reference by 1db each for the three LM3915s. That fixed the top end, but I think you need to move the "ground" end by 3db also. If not the three meters will be at the same level at a low end reading.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top