Author Topic: Easy to build Polyphonic MIDI Interrupter  (Read 2497 times)

Offline Max

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Re: Powerful easy to build MIDI Interrupter
« Reply #20 on: May 20, 2020, 12:15:43 PM »
Good morning,


The impact of the optimizations was actually bigger than I thought (should probably have waited with my last reply...).  I can now play 8 voices with less jitter than before.

This time I tested it pretty hard, passing all 16 MIDI channels to the interrupter, which should play on all 6 outputs around 6-10 notes from 4 out of the 16 channels (the other 12 were only to see if it processes the data fast enough) Result: noisy, but no missed notes. That noise increases with the output count, so you should use a Tiva firmware with as few outputs as possible. If you don't use one of the outputs, unassign all channels; this helps reducing the noise. With only one or two outputs, which will propably the case for most people, you can barely hear any noise.

I've successfully tested release v3.0.1 on my DRSSTC (static load) for over an hour with all kinds of MIDI files and I really like the way it sounds. I'll probably edit this tomorrow but as of now I think I'm pretty much done with the code. I do have some ideas for future improvements but honestly I'm too happy with the current state to start working on something new.  ::)

This video demonstrates pretty much everything. Just to remember, this is an unmodified MIDI file I found when searching for the song. Simply pass the channels you like to the interrupter, and you get this. Many voices, fast notes, ADSR, effects. Note that I reduced the constant duty for low notes at around 01:00 to protect my poor breakers  ;D

While the video above is for sure more impressive, I wanted to share this one too, because a) I have an earworm and b) I really like the staccato ADSR sound. The slight reverb comes actually more from ADSR than from the metal / the room.


I'm really looking forward to the next possibility to run the setup as tesla coil again, instead of cooking some steel...


Kind regards,
Max
« Last Edit: May 20, 2020, 05:40:04 PM by Max »

Offline futurist

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #21 on: May 21, 2020, 12:16:04 AM »
I ordered dev. board and display and I'm eager to give some feedback :)

Offline Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #22 on: May 21, 2020, 07:46:28 PM »
Note to myself: extensive testing is not complete testing. While playing around with the interrupter today I found a couple smaller issues. Nothing critical though. As always, you'll find the current release and what's changed on GitHub: https://github.com/MMMZZZZ/Syntherrupter/releases/

An interesting observation: While my oscilloscope tells me that duty cycle limiting works, there are some note combinations that cause really high peak input currents. I already noticed a long time ago (before this project) that same duty does not mean same power. So it could simply be a particular "bad" combination within the limits... I'm interested if this will cause bigger arcs, too. However, it looks like ironically, I will not be the first one to produce any arcs with my interrupter  ::) It'll take weeks until I get access to a decent test location.

Edit: Just wanted to notify everyone that I rewrote the first post. It is an almost complete documentation of the Syntherrupter's features*. I'll add the missing bits over the next days.
*which it already was more or less for firmware v1.x, but that wasn't really helpful anymore.


Kind regards,
Max
« Last Edit: May 21, 2020, 11:46:47 PM by Max »

Offline Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #23 on: May 24, 2020, 12:12:36 PM »
While I use MIDI over USB-UART only, others would certainly like to have a direct MIDI input. Since MIDI uses an oddball baudrate of 31250, which most USB ports are not capable of, that feature requires a second UART. Yesterday I realized that this is actually pretty simple to add. Result: It can now receive MIDI data over the USB UART, or over the Rx/Tx Pins PC4/PC5 at 31250bps. Note that the data of both UARTs ends up in the same buffer. Therefore make sure only one of the ports receives data at the same time otherwise it'll be scrambled together.

Unfortunately I have no MIDI cables or optocouplers I'd need for testing. So in case anyone has the motivation and materials needed, I attached the binaries.
Edit: Attachment removed since it has been published on GitHub. Please check the release page for the current firmware.


Kind regards,
Max
« Last Edit: July 04, 2020, 12:14:40 AM by Max »

Offline futurist

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #24 on: June 13, 2020, 10:39:23 AM »
Finally received dev. board and display and I have few questions

What is the best way to power everything? USB or internal battery?
Do I need any additional switches, power switch, or safety switch for turning off outputs?

Before I do anything I have to ask my local machinist to cut out a hole in aluminium enclosure for the display

Offline Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #25 on: June 13, 2020, 01:25:41 PM »
Hi futurist,


The best way to power it is over USB. That can be your PC (500mA min!) or a powerbank. A normal battery is problematic since the Nextion display requires regulated 5V, otherwise you damage it! With this in mind I oped for the powerbank; cheap, regulated and with charge controller.

The software has a safety feature integrated which turns all outputs off if you hit the white background below the control sliders. If you don’t trust that you can of course add a safety switch which cuts the supply or the connection to your optic transmitter(s).

Although there is a standby function which turns off the display backlight, it is not a soft power off. So if you‘re using batteries, you need a power switch.

The hole for the display... yeah I wanted to do it on a CNC to get a nice chamfer around. But thanks to lockdown I ended up doing it by hand. Looks better than expected!


Kind regards,
Max


Offline futurist

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #26 on: June 13, 2020, 03:42:50 PM »
Thanks Max, I'll go with USB power and won't bother with batteries

How did you cut hole for the display? Turned out very nice

Offline Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #27 on: June 13, 2020, 04:26:50 PM »
Thank you!

I used a dremel to cut a first window, leaving around 3mm to 5mm on each side. And then filed, filed, filed. First with a rough one, to remove the material, then took it with a finer to the final dimensions.  Finished with 800 grit sand paper to break the edges.
Finally, if you have no chamfer you might want to paint that "vertical inner" surface of the hole in black. then it doesn't look as thick (I forgot to do it...). Material thickness is 3mm btw.

Kind regards,
Max
« Last Edit: June 13, 2020, 04:29:42 PM by Max »

Offline Mads Barnkob

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #28 on: June 22, 2020, 10:21:15 AM »
It seems like mouser is the best bet to get the parts from the same place, at least for me.

But I can not get the 5.0" 800x480 version of the display, only if I take the 7.0" can I get that resolution. Would that work?

The Tiva kit seems to be the same price everywhere.

I like the screw fibre optic transmitters and receivers, so thought about trying out these broadcom ones, not cheap, but not SUPER expensive either. Mouser does not sell the IF-D97 / IF-E97 anymore :(

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Offline Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #29 on: June 22, 2020, 11:02:24 AM »
Hello Mads,
 
 
Yes, Tiva is pretty much the same price everywhere. Except that in the TI store you don‘t pay taxes. Don‘t ask me why. And it passed customs with no problems either. This however only makes sense if you order >2 boards.

I like the screw fibre optic transmitters and receivers, so thought about trying out these broadcom ones, not cheap, but not SUPER expensive either. Mouser does not sell the IF-D97 / IF-E97 anymore :(
What a bummer. I haven't seen them anywhere else. Or at least not for <10$.

Oh I didn't know Mouser has Nextion displays - or at least a few of them. As long as your display is a genuine Nextion one (seems to be the case) and has a resolution of 800x480 it should work almost (!) out of the box. You have to open the Nextion file in the editor and change the device to your model. Since the resolution is the same, no other changes are necessary.
You‘re right, Mouser doesn‘t have the 5 inch version. The 7 inch version is from the "Enhanced" series (instead of the "Basic" series) which offers a few more features and costs ~20$ more. If you really want to get it as soon as possible no worries, AFAIK it will work just fine. Just know that those features (like GPIO pins or a RTC clock) are useless since the firmware is written for the "Basic" version which doesn't have them.
Otherwise I would recommend to order the display directly from the manufacturer. Saves you ~20$ for the 7inch or ~30$ for the 5inch display.
The Nextion Touch display can only be ordered from their site: https://www.itead.cc/nextion-nx8048t050.html
You can find them on ebay, however that are incompatible twins - always. They look the same but they're only meant for the chinese market and can't be easily programmed.
[...]
Edit 2: You could actually buy the 7inch model (65€) instead of the 5inch one (56€). Both have the exact same resolution, therefore no changes to the GUI are needed. Depends on whether you prefer bigger buttons and fonts or a more compact interrupter  :)


Kind regards,
Max

Offline Mads Barnkob

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #30 on: June 22, 2020, 12:33:51 PM »
I was also pretty sure I had read somewhere in the thread that you said the 7" would be usable as well. So I searched for "display" and 7", but did not find it, because you wrote 7inch :)

I will try it out with the 7" and just get it all from mouser for making it easier for myself. It is after all the opto parts that make up the biggest part of it anyway. Unless I find a cheaper alternative, not ordering right away :)
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Offline AstRii

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #31 on: July 02, 2020, 05:34:23 PM »
Looks so nice, great work!
I would love to build one, but before i go and buy the components i have a couple of questions.

I can't see a reason why not, but just to be sure, can you use a software like FL Studio to send the MIDI data to the interrupter? Or what software would you recommend?

You said the output pins from the board to the optical TX are 3.3V @2mA, so i guess i also need some transistors to switch the 100mA OPF1412T right?

Offline Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #32 on: July 02, 2020, 07:04:55 PM »
Thank you very much AstRii!


I can't see a reason either :) You can try it out before building one. Install the program "loopmidi" (Details in the first post. Maybe use CTRL-F to find it quickly) and check if FL Studio finds the virtual MIDI port.

You're right, the pins can only provide 2mA. In further revisions I might be able to increase it to 8mA, but not sure. So yes, you definetly need a driving transistor.


Kind regards,
Max

Offline AstRii

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #33 on: July 02, 2020, 11:17:48 PM »
Ok i checked, FL Studio does recognize the virtual port. So i just bought the components from the links you provided. Can't wait for them to arrive :)

Offline Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #34 on: July 04, 2020, 12:17:47 AM »
Good evening,


I released a new beta firmware. I won't be able to do any testing for a couple weeks but since there are no "safety relevant" changes, I see no risk in using it with a tesla coil. The only thing I do not know is if the new features work as expected.

The most important changes are support for MIDI "Expressions" and custom pitch bend ranges. Expressions are used for nuances, like crescendos (increase in volume). Some pieces set a custom pitch bend range f.ex. to perform larger "sweeps". Until now this sounded awful and made the file or at least parts of it completely unusable.
Of course, the additionnal MIDI UART is part of this release, too (see previous post).

As always, the details are listed on the GitHub release page.

@AstRii: Looking forward to your experiences with FL studio!  :D


Kind regards,
Max
« Last Edit: July 04, 2020, 01:25:52 AM by Max »

Offline Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #35 on: July 09, 2020, 09:09:08 PM »
Good evening,


As I said in my last post I currently do not have access to my interrupter, so I couldn't test anything. However, I found a spare Tiva LaunchPad so I can at least test with speakers.

First of all, the untested beta I released with the last post contains some dumb copy paste errors making it useless. I hope I fixed all of them by now (still can't test the MIDI input).
Just to be clear, the latest stable release is absolutely fine and contains none of those errors.

Now the interesting part. I added a new feature, stereo sound! You can place each coil with a slider between "left" and "right". If the MIDI file uses the pan command you can hear how the sound moves from left to right or vice versa. When testing it (with speakers), I liked it so much I wanted to build a second DRSSTC to get that effect  ;D Ok, admittedly it is not better than normal stereo but still. Imagine up to 6 coils in a row and a "wave" of music going through them.
You can disable it if you want. In that case the coil ignores the "position" of the sound. This is the power on default.
Picture of the new menu with the slider:


While playing around with the code I found that pitch bend is actually not that smooth at all. I never really noticed it, but with the latest changes it got worse for some reasons. I realized quite soon that the way I generate the output signals was absolutely not "pitch bend friendly". So I rewrote it in parts and pitch bend is now as smooth as it can be. I think I managed to get an overall better sound quality but especially with many voices (and I mean full 8 voices on all 6 outputs) it may sound a bit worse in some cases. Shouldn't be a big issue though.

Since I tested it as good as I could I released a new beta. It still has the beta status because the MIDI UART is untested. As I said way back, I have no possibilities to test it. Other than that I'd consider it safe to use.
All details on the GitHub release page.


Kind regards,
Max

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Re: Easy to build Polyphonic MIDI Interrupter
« Reply #35 on: July 09, 2020, 09:09:08 PM »

 


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