8th Note blog - audio related DIY electronics

Display ideas for a "display-less" attenuator

It is possible to make diyplays for the 8th note Attenuator.
The headers area big help in this, as the LEDs of the attenuator can be mounted externally to an enclosure front plate. But there is more. It is possible to read the volume level from a digital port marked DO on the panel.

As this is a digital method, displays for the 8th note attenuator need a microcontroller or Arduino board and some programming.

Currently no out of the box display but I will help anyone who want to make one. Reading the digital value of the attenuation level (volume) means it gives back a value between 0 and 127.

You can do anything with that, display it on a LED bar, on a Character display, or any clever light feedback You like.

I never was a fan of numbered displays. I have yet to see one that turned out nice. Until that I am only interested in LED displays. 

I try to show some ideas here:

Background ring using the external LED output

Background ring using the external LED output

External LED driver showing attenuation position

External LED driver showing 128 attenuation position on 64 LEDs

External LED driver showing 64 attenuation position on 64 LEDs

I hope You like one or get an idea for your own display.
Making one is not that difficult, and if there is more interest I will develope an universal chip to make a few types of displays without programming skills.

But now, it is time to understand a little bit what is behind.
I try to make it beginner friendly.
Even if you are not familiar with programming, it is nice to understand what is behind.

But what is possible at the first place?
a) Using the LED headers without any additional circuit status LEDs can be mounted as an indicator on the faceplate or as back-light.
b) With additional circuits, it is possible to make a LED bar turn on and follow the level of attenuation (volume).
c) When doing this with a lot of LEDs, mounted around the pot itself it can even follow the pot position.
d) The last solution could be a character display with seven segment LED displays, or a more advanced text based character display.
e) Any cool idea of yours...

The a) is already covered by the documentation (check www.8thnote.eu), it needs no additional parts but the LEDs.
The d) is out of the scope of this text but the point is, you can do whatever you want when you already get some data out. Lets see how.

Getting information out of the attenuator is possible on two headers:
1. LED header
2. DO header

1. The LED header is the simplest, with a state check, a pin next to the LED can be checked against GND.
This can tell the same information as the LED status. Thus we can read which channel is selected, if mute has been pressed, or if LULO is on (pot or remote is master).
Later we can use this information as variables (true or false) in our program, and do whatever we want. Turn on lights, or send a message to a display.
To a microcontroller it is as simple as it gets:


2. The DO header is an SPI communication port that outputs a coded word on each volume change. This code can be decoded to get the attenuation level 0-127 or 0dB-64dB.
The data can be read with a microcontroller, and processed to get a single number variable. It is something like...:


If we have the attenuation level, we can easily do actions according to it:
Lets see if we have a LED bar like this (Seed Grove LED bar).


It has 10 LEDs. Let it have the bottom red LED indicating only the level 0 or MUTE. So we have 9 LEDs left for indicating 127 levels. Easy math, 127 / 9 = 14,11 so we will have one LED for every 14 setting.
Actually we will have one LED for level 1, 14, 28, 42, 56, 70, 84, 98, 112, 126
Now you only need a small code that checks the current level, and light up LEDs according to that level.
For a real circuit, you need transistors or a LED driver too, because no microcontroller outputs are designed to drive LEDs.

Using lots of LEDs in a circular arrangement is very cool. See images for a real example of the above idea #4 or idea #5.
It is an advanced version of the LED bar above if you believe it.

This one or a similar panel I will make opensource / free to copy / if it is ready.