Help to design a Vu-Meter with this special Led Display (see the pict enclosed in the post)

Thread Starter

Clomifuge

Joined Jan 16, 2022
36
Hi all and happy new year.

I need help to design a Vu-Meter with this common Anode led display, I imagine I need to use HC595 and a MCU, but I don't have a big experience with this king of technology.

I can pay for the time and the works and expertise. I already did the Audio buferisation circuit and RMS detector I just need the LED Drive.

This led display was used in a Vu-Meter by a Chinese company (see the pics of the PCB enclosed) but I don't have schematics and I prefer do one myself.

Thanks by advance.

Capture d’écran 2022-01-20 à 13.06.33.png


IMG_0803.jpeg
 
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Thread Starter

Clomifuge

Joined Jan 16, 2022
36
What VU levels are you planning to use for each LED level?
Is it in logarithmic steps? As in deciBels?
Hi Lan0 and thanks to you for your reply, in fact I already did the Audio circuit it will be Log steps and with Vu and Peak display switch, I already use this circuit with a LM3914, bu in this case I imagine I can't use a LM3914 because I need serialization.
 

Ian0

Joined Aug 7, 2020
4,821
Hi Lan0 and thanks to you for your reply, in fact I already did the Audio circuit it will be Log steps and with Vu and Peak display switch, I already use this circuit with a LM3914, bu in this case I imagine I can't use a LM3914 because I need serialization.
But the LM3914 has linear steps. Have you already built a logarithmic amplifier to drive the input?
 

Ian0

Joined Aug 7, 2020
4,821
So the LM3914 just measures a linear voltage.
I have an idea rattling about in my mind that you should be able to do this with a single LM3914 and a 4017.
The 4017 divides by 3 and drives the display anodes, via emitter followers, and also switches in different thresholds to the RLO and RHI inputs, probably with the help of a 4052.
It depends on how quick the LM3914 is, and I don‘t think that the datasheet tells you. I suspect it might be made of the same stuff as the LM339 and an LM339 is quite speedy.
Bon chance!
 

Thread Starter

Clomifuge

Joined Jan 16, 2022
36
So the LM3914 just measures a linear voltage.
I have an idea rattling about in my mind that you should be able to do this with a single LM3914 and a 4017.
The 4017 divides by 3 and drives the display anodes, via emitter followers, and also switches in different thresholds to the RLO and RHI inputs, probably with the help of a 4052.
It depends on how quick the LM3914 is, and I don‘t think that the datasheet tells you. I suspect it might be made of the same stuff as the LM339 and an LM339 is quite speedy.
Bon chance!
Hi

Really ? it will be a very nice solution, have you got a schematic exemple ?
 

bassbindevil

Joined Jan 23, 2014
371
I've been gradually building an LED RTA that drives a matrix of 70 LEDs using a 4017 and LM3915; it's the Gold Line ASA10 from plans in Popular Electronics back in Sept 1979. Possibly a bit obsolete in an age where a cheap Android tablet can do real-time spectrograms, but with modern high-efficiency LEDs it should make a nice light show.
https://web.archive.org/web/20161120012740/http://www.gold-line.com/asa10b.htm
https://worldradiohistory.com/Archive-Poptronics/70s/1979/Poptronics-1979-09.pdf
There's a better scan of that issue at Archive.org, with a more legible schematic, though the PCB artwork is still too blurry to be used.
https://archive.org/details/197909PopularElectronics/page/n65/mode/2up
Here's the 600 dpi scans of the PC board artwork from an original magazine (scanned in 1999), on the very small chance someone else ever wants to build this.
rta_LED1.gifrta_LED2.gifrta_main.gif
 
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Marley

Joined Apr 4, 2016
468
So you already have the linear part of the circuit designed and built.
This LED array is multiplexed so will need to be constantly scanned.
The best way (least parts count) to convert the linear voltage to a scanned display is to use a small MCU that has an ADC on the chip. You could set the voltages at which each LED lights in a look-up table in software. You could do the attack and decay timing in software too.
Trouble is - for a logarithmic display you probably need a good 16-bit converter - might be difficult to get in a small MCU.
Alternatively, use a dedicated ADC chip and use the MCU for interfacing with this chip and driving the display.
 
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