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 Forum index » DIY Hardware and Software
Eurorack friendly VU Meter?
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AlanP



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PostPosted: Wed Oct 09, 2019 4:55 am    Post subject: Eurorack friendly VU Meter? Reply with quote  Mark this post and the followings unread

I'm currently brainstorming a new output mixer (strong inspiration from the Buchla 227), but one stumbling block is a VU meter for each channel.

The undoubtedly coolest ones would be a moving-needle type (with a coil, like an old analog multimeter), but they cost a lot per unit, and also take up a lot of panel space. In eurorack, the space taken is the biggest problem.

A line of LEDs might work... but they don't look as cool, you can't see small movements in signal volume level, plus they need a bargraph driver chip each, to my understanding. (LM3914 or the like.)

I'm curious as to other folk's thoughts.
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JovianPyx



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PostPosted: Wed Oct 09, 2019 7:27 am    Post subject: Reply with quote  Mark this post and the followings unread

I put far less priority on "looks cool" than most folks. D'arsonval meter movements may in fact be the more functional and accurate of VU types.

There is also the dual color LED method. My Scarlett 2i4 has such a LED arrangement around the gain knobs. At normal levels it is green. Turns yellow near clipping and red when in clipping. No it's not as cool looking as the gauges and meters in a 1950s scifi spaceship, but I find it very easy to limit clipping using just the LED. That may be the best choice for your purpose - very small, yet can stop clipping. You don't really need to know that your signal is +7.39 dB to know it's clipping. Just the red LED is all that is needed.

D'arsonval - expensive, huge and lethargic - steady-state accurate (if good ones and calibrated)
line of LEDs - less expensive - shows levels other than clipping
single dual color LED - least expensive - shows what is needed.

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Electric Druid



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PostPosted: Wed Oct 09, 2019 2:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

I had a similar problem, so I did a PIC-based VU meter. Actually, I needed something that showed me when I was about to hit clipping, so it's a peak level meter or something, not a VU strictly. The nice thing about doing it in firmware was that I was able to add an optional 'peak hold' dot above the meter, so you don't miss brief transients (which is a definite weakness with moving coil meters - they take *ages* to react!).

More details, code, schematic, etc are here:

https://electricdruid.net/led-bargraph-audio-level-display/

My version was mono (that was what I needed) but it'd be pretty easy to extend it to a stereo version on a slightly bigger chip - one 28-pin DIP, say.

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Grumble



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PostPosted: Wed Oct 09, 2019 2:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

You could use a small oled display with an Arduino.
On the display then you can draw a Vu meter when necessary, or display other things.

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diablojoy



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PostPosted: Tue Oct 22, 2019 12:32 am    Post subject: Reply with quote  Mark this post and the followings unread

Maybe this
https://www.tesseractmodular.com/eurorack-modules/blinks

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Grumble



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PostPosted: Tue Oct 22, 2019 12:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

https://youtu.be/v3d3x88pb9A

this Laughing

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AlanP



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PostPosted: Tue Oct 22, 2019 12:56 pm    Post subject: Reply with quote  Mark this post and the followings unread

The OLED and LED strip are cool, but have either too much extra circuitry for what I want to do, or take up too much space. (The eternal curse of Eurorack, no space for anything.)

I think I'll go with Scott's indicator LEDs. A red wun for overload, and a green for signal level, perhaps.
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Blue Hell
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PostPosted: Tue Oct 22, 2019 2:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

Or even more compact would be a bicolor LED, which you could make to fade from nothing trough green, then orange and finally red .. I'm sure PHOBoS would have some idea about how to control that at no cost and no volume Cool

oh .. and .. https://www.avrfreaks.net/forum/fading-bicolor-led for how to do it with a processor .. you could prolly control a bunch of 'm then.

Some more ideas about that : https://stackoverflow.com/questions/15803986/fading-arduino-rgb-led-from-one-color-to-the-other

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also .. could someone please turn down the thermostat a bit.
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Blue Hell
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PostPosted: Tue Oct 22, 2019 2:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Oooh .. nice : http://lednique.com/gpio-tricks/1-gpio-dual-led-common-cathode/

And then to avoid the processor at all .. voltage to PWM is not too hard with discrete stuff .. basically a saw generator .. or saw like .. so CMOS could do that ... and then a comparator for each PWM output ... you'd then need a rectifier circuit for each channel .. ideally RMS .. but prolly a diode a cap and a suitable resistor to load it would be nice already.

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also .. could someone please turn down the thermostat a bit.
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PHOBoS



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PostPosted: Wed Oct 23, 2019 2:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Blue Hell wrote:
Or even more compact would be a bicolor LED, which you could make to fade from nothing trough green, then orange and finally red .. I'm sure PHOBoS would have some idea about how to control that at no cost and no volume Cool

hmm,. PWM and an inverter so at 100/0 green is full on red off,. 50/50 green and red at 50%, 0/100 red full on green off, and everything in between of course.
maybe some peak detection for red. A saw + comparator should work to control the dutycycle with a signal. I guess it would need something extra to set the
brightness so it isn't on with no level, maybe some more PWM for that.

Blue Hell wrote:
Oooh .. nice : http://lednique.com/gpio-tricks/1-gpio-dual-led-common-cathode/
And then to avoid the processor at all .. voltage to PWM is not too hard with discrete stuff .. basically a saw generator .. or saw like .. so CMOS could do that ... and then a comparator for each PWM output ... you'd then need a rectifier circuit for each channel .. ideally RMS .. but prolly a diode a cap and a suitable resistor to load it would be nice already.

yeah, like that. Very Happy

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PHOBoS



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PostPosted: Wed Oct 23, 2019 2:21 pm    Post subject: Reply with quote  Mark this post and the followings unread

I think using seperate LEDs would give a better indication though, so one or two LEDs for level, and an LED for clipping.
I actually did design a 3 LED level meter using a quad opamp years ago. It might need some tweaking but I'll see if I can
dig up the schematic.

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ixtern



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PostPosted: Fri Oct 25, 2019 3:40 am    Post subject: Reply with quote  Mark this post and the followings unread

Once upon a time I've bought on Aliexpress small, cheap and cool LED stereo level-meter. The only problem is that I don't know so far how to use it in eurorack, as it is provided with (and for) microphone and I can't figure how to do the eurorack input instead of the mic.
https://www.aliexpress.com/item/32950090988.html?spm=a2g0s.9042311.0.0.27425c0ftzydML
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PHOBoS



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PostPosted: Fri Oct 25, 2019 7:29 am    Post subject: Reply with quote  Mark this post and the followings unread

cute, but 2 bars and only 1 mic ?
The chip looks to be a microprocessor (15W402AS) and I see a button so I guess it has different modes and the LEDs for both bars are just in series.

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weasel79



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PostPosted: Fri Jan 17, 2020 6:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

going back to "led stripes" you could realize tiny RGB LED chains with the 2020 smd version of ws2812 or similar. needs some kind of MCU (teensy or esp32 with ADC i guess) but no other extra circuitry.

check these LED rings i made at some point. pretty sure this would look awesome in a couple 10-20 segment meter stripes. granted RGB funcionality is a bit overkill for that application but hey there's a lot of stupid fun feature ideas to explore for your mixer..
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