Teensy/Arduino vs Midibox for a synth controller

MIDIbox NG
1

Hey,

frist, thank you for this wonderful project.

I’m trying to decide between teensy and midibox ng for a universal synth controller. I would like to have around 40 pots/faders, a 20x2 lcd with 4-5 encoders, 10 buttons with leds and a few rotary switches.

I did a test with teensy 3.2 and 8 pots connected via a CD74HC4051E. The cable length was around 50cm between the pots and the multiplexer to test a real world scenario in a big case. But unfortunately there was a lot of noise. Even with heavy software averaging i got jumping values +/-1 for 0-127 values.

Do you think there would be less analog noise using midibox?

Thnak you

2

Upcoming project : http://wiki.midibox.org/doku.php?id=mb-modulbox-ng
Might interest you.

bests,
JK
 

3

and about noise issue:
http://ucapps.de/mbhp_line_driver.html

Bests,
JK

4

MB-Modulbox NG looks intresting. Would you recommend it for a classic synth layout (like a Minimoog Voyager) too?

5

Regarding the noise issue. I found this article http://www.midibox.org/dokuwiki/doku.php?id=troubleshooting#how_can_i_avoid_pot_flickering_jitter

There it says

Quote

*Update:* most of these hardware countermeasures are not necessary anymore, nearly all built MIDIboxes are working from the first startup without any jitter problems, since I improved the software on a way that it can handle with jitter.

So starlike wiring and short cable lengths not needed anymore?

6

Just now, tago said:

MB-Modulbox NG looks intresting. Would you recommend it for a classic synth layout (like a Minimoog Voyager) too?

That’s a goal of the project to be compatible with old school analog synths. So totally yes.

http://ucapps.de/mbhp_ainser8.html < This module allow to have cool analog in from pots. Encoders use http://ucapps.de/mbhp_din.html .

You should keep an AINSER8 as near as possible of Pots.then link AINSER8 to core32.
The line driver module allow to have distance links without loosing signal strenght, that’s why i talked about it. but not the right thing to use here.

Best regards,
JK

7

Hi all

1 step jitter for 7 bits (128 value) is huge !!! it’s more than 40mV for 5V supply,

there is for sure and issue with your build.

Keys for low jitter:

-A perfect grounding, with same 0V reference for both servo and AD chips Vref

-Quality power supply with low ripple, good line and load regulation, optional sense is a must

-shorter wire as possible

-optional low pass RC filter can be added

 

Following all this for my build, running AIN at 11bit (2048 steps) give very low jitter, less than 1 step value change per sec, around 2mV jitter.

So the system is finally configured at 10bit … rock solid !

Best

Zam

 

 

1 Like
8

Thank you for your suggestions. Yes, for 7bit its too much jitter.

I attached a photo of my setup (sorry its a mess). Cable length between multiplexer and 8 pots array is 50-60 cm. That cable has a additional connector in between after 50cm without any purpose. Can’t remember why i did this. The wiring seems correct since its working.
The teensy is powered via usb from a tablet computer, no additional power supply.

 

 

DSC0379.jpg.9b3b0aa90a847eb38ae0902cc7152568.jpg
DSC0379.jpg.9b3b0aa90a847eb38ae0902cc7152568.jpg1958×1102 752 KB

9

multiple AINSER8 vs single AINSER64

If i understand right you would recommend multiple AINSER8 boards over a single AINSER64 in order to keep the cable lengths to pots/faders as short as possible? My front panel would be something like 80x25cm.

10

Hi tago

“simple” design only allow two chips/line for J19 SPI port, you can do more with modification.

If, as you say, you need at least 40 pot/fader you better go with the 8x8 multiplexed version (AINSER64).

If you want better jitter performance for sure you build is a mess, I suggest you to monitor your servo ref voltage first, you will see how it move…

If you respect the keys I give before, you can have 50 cm wire between pot and ADC (that’s what I have considering trace at both pcb and the wire).

If everything else is strong the only drawback with long wire is the voltage drop, but it will be constant and you can map/scale value at soft side

Also I’m not sure but I don’t see any capacitor with your build, maybe your jitter come from chips/line/clock noise going all around your build

2 minutes ago, tago said:

The wiring seems correct since its working.

No it’s not , I don’t call more than 1% jitter a working system

 

Best

Zam

11

29 minutes ago, Zam said:

Also I’m not sure but I don’t see any capacitor with your build, maybe your jitter come from chips/line/clock noise going all around your build

I tried capacitors between ADC pin and AGND beside software tuning like suggested on teensy forum, but no luck.

 

31 minutes ago, Zam said:

No it’s not , I don’t call more than 1% jitter a working system

You’re right it’s only working in principle.

12

What ready to use power supply module do you recommend?

Is a switching power supply ok?