PIC LED VU meter

[ruffrecords]

Hi John,
Another idea, and test ...

Cheers,
Pascal

Looks good to me.

Cheers

Ian

 

[Andy Peters]

Hi John,
Another idea, and test ...

The question is whether you can update the display fast enough ...

 

[plimousse]

Hi Andy,

"A volume unit (VU) meter or standard volume indicator (SVI) is a device displaying a representation of the signal level in audio equipment.
The original VU meter is a passive electromechanical device, namely a 200 µA DC d'Arsonval movement ammeter fed from a full wave copper-oxide rectifier mounted within the meter case. The mass of the needle causes a relatively slow response, which in effect integrates the signal, with a rise time of 300 ms. ...
The VU-meter (intentionally) "slows" measurement, averaging out peaks and troughs of short duration, and reflects more the perceived loudness of the material than the more modern and initially more expensive PPM meters."

With a PIC, we are 100 * faster (No ?) ;-). I'm working on more capacity display, with graphics.
We can display 1, 2, ... 4  bars with Peak memory, etc

Cheers

 

[JohnRoberts]

The question is whether you can update the display fast enough ...

Fast enough for what?

I used an intentional 4mSec attack time on Peak signal (same as PPM)  and 200 mSec attack on Ave/VU. With 200mSec release on both so both would decay in lockstep when music stops.

So even a slower than dirt SPI would delay the display to lag after actual audio signal. Further a too slow sample update, would make the display look jumpy if signal changed too much between display samples.

I don't even recall what spi clock frequency I used but I probably pushed all 64 bits of LED data in series (to KISS). Even updating 4x16 LED meters appears real time and continuous. Note: our eyeballs are not all that fast.

here is link to old  video file  http://www.johnhroberts.com/Candy.wmv

I don't hear the sound in my computer after it converts to a mov file but the meter is reading a song from my friends old band.  All four meters are being updated but only two have music playing , one has a steady sine wave, and the other no input so you can see lack of crosstalk  S/H settling time issues.

JR

 

[Andy Peters]

With a PIC, we are 100 * faster (No ?) ;-). I'm working on more capacity display, with graphics.
We can display 1, 2, ... 4  bars with Peak memory, etc

What I meant was: can you write to/update the display fast enough so that your eye doesn't detect artifacts.

Last time I did this sort of thing I had a frame buffer in the micro large enough to hold the entire image. It was a 128 x 64 monochrome display, so 8k pixels. Writing a byte set or cleared eight pixels, so the frame buffer was 1k bytes. All of the calculations determined which pixels to set or clear and the frame buffer was updated accordingly. Then a timer task ran which updated the display from the frame buffer. Updating the display involved 1k byte writes, so for a 30 fps update rate,  that meant writing a new byte every 32.5 μs. That's a piece of cake on an 80 MHz ARM. I have no idea whether you can do that in a 16 MHz 8-bit PIC.

So as long as your micro can do the math and update the frame buffer in a reasonable time, it's all good.

 

[JohnRoberts]

What I meant was: can you write to/update the display fast enough so that your eye doesn't detect artifacts.

Last time I did this sort of thing I had a frame buffer in the micro large enough to hold the entire image. It was a 128 x 64 monochrome display, so 8k pixels. Writing a byte set or cleared eight pixels, so the frame buffer was 1k bytes. All of the calculations determined which pixels to set or clear and the frame buffer was updated accordingly. Then a timer task ran which updated the display from the frame buffer. Updating the display involved 1k byte writes, so for a 30 fps update rate,  that meant writing a new byte every 32.5 μs. That's a piece of cake on an 80 MHz ARM. I have no idea whether you can do that in a 16 MHz 8-bit PIC.

So as long as your micro can do the math and update the frame buffer in a reasonable time, it's all good.

There is a big difference between 8k pixels and only 64 bits.  While I wouldn't use an 8-bit micro unless somebody was holding a gun to my head. 

I posted a link to a video of the APB console meter prototype playing music on my bench (above).

JR

 

[Andy Peters]

There is a big difference between 8k pixels and only 64 bits. 

True,  but the display Pascal used is a graphic LCD that's 128 x 64 pixels, and he drives it from a PIC16F.

While I wouldn't use an 8-bit micro unless somebody was holding a gun to my head. 

Especially not an 8-bit PIC! (Like the PIC16F.)

 

[metalb00b00]

Found this interesting PIC16F1847 VU meter project (it's in Czech language tho...)

http://s-o.webnode.cz/vu-metr/vu-metr-s-neopixel

at the end of the page is a link to download the assembly source code file.

Surely someone who is an expert PIC programmer can modify it to turn on/off standard LEDs instead of a daisy chained Adafruit Neopixel sticks.

oh nevermind... my bad. assembly code is some kind of a boot loader. the actual program is already compiled as a binary hex.

 

[plimousse]

Hi Guys,

I found this product Evor04 ...
Please see the attached datasheet, and give me your opinion ?
Raisonnable price :  65.40 EUR 75.00 USD

Cheers,
Pascal