Author Topic: Syntherrupter - A Feature-rich, Polyphonic Interrupter  (Read 20466 times)

Offline futurist

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Re: Syntherrupter - A Feature-rich, Polyphonic Interrupter
« Reply #160 on: June 06, 2021, 11:18:46 AM »
Looks nice! I like the idea of having switches to physically turn off outputs, maybe even add one master switch for all outputs?
Is the board designed to fit in particular enclosure?

Offline Max

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Re: Syntherrupter - A Feature-rich, Polyphonic Interrupter
« Reply #161 on: June 06, 2021, 03:01:44 PM »
Thanks! Good idea with the emergency switch. I also added the missing infos on the silkscreen. This layout is btw not suited for self-manufacturing since a couple holes need to be plated. If there's interest in such a version, I can try to make one.

No, it's not made for a particular enclosure. I designed the PCB "as compact as possible" and the next biggest size was 100x160mm which is a very common size (eurocard). Thus there should be many different enclosures available.

Kind regards,
Max

Online Mads Barnkob

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Re: Syntherrupter - A Feature-rich, Polyphonic Interrupter
« Reply #162 on: June 06, 2021, 08:41:31 PM »
I like the idea of making it a PCB that the Tivo plugs into, I did not think of that!

I think some of your resistor values will need tweaking when running on 5V, I had to change some of my initial design as it was too high values for my LEDs, but yeah that differs from build to build what parts are used and how bright you want something to be that sits in a dark room.

You could add a row of pin headers for external interrupters and a DIP switch row to select which is used, might not be for everyone, but I am making that on my build. Since optical outputs are money, might as well make them useful in more ways :)

My final exam was Friday two days ago, im done with studying next work, which I have been doing for 3 years, so I can finally pick up on my DRSSTC show controller again :) https://highvoltageforum.net/index.php?topic=1417.0
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Offline Max

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Re: Syntherrupter - A Feature-rich, Polyphonic Interrupter
« Reply #163 on: June 07, 2021, 12:12:07 AM »
I can see how having the option of an external interrupter could be handy... However, I don't think it needs these changes. I'll add a high-impedance mode in software, turning the output pins into inputs, then you can connect your external interrupter directly to the pin header on the Tiva board itself.

Could you be a bit more specific about the resistors? Here are my calculations behind the values:
560R base resistor: Desired base current: 5mA. (3.3V_pin_high - 0.6V_base) / 5mA = 540R
68R IR transmitter: Desired LED current: 40mA (nominal current: 60mA). (5V - 1.7V_f - 0.6V_ce) / 40mA = 68R
270R LED resistor: Desired LED current: 10mA. (5V - 2V_f - 0.6V_ce) / 10mA = 240R
Actually, I could change the 270R for a 220R; getting rid of one resistor value since 220R resistors are required for the MIDI In/Out circuit anyways.

I added a pin header for a MIDI Out port which might be used in future. I also added the footprint for one of these generic SD card breakout boards.

Congrats for your exams!


Kind regards,
Max
« Last Edit: June 07, 2021, 12:17:08 AM by Max »

Offline Max

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Re: Syntherrupter - A Feature-rich, Polyphonic Interrupter
« Reply #164 on: June 18, 2021, 01:22:10 AM »
Hello everyone,


I took a little break from the PCB design and worked on an issue Syntherrupter basically has since the day it learned playing more than one note at the same time. So far the generation of the output signal happens in real time: if (time > notePeriod): generateOntime(); (overly simplified, but enough to get the idea). The big issue is that any sort of processing elsewhere in the code always has a direct impact on the output. You can test it in the current beta; every sysex command you send to Syntherrupter will cause a short pause in the output. On a smaller timescale, the regular processing which only takes 30-70us is already too much jitter in the output. This is especially noticeable in simple mode. If you play around for a bit you'll for sure find frequencies that sound "not-so-clean" or straight out awful. There's also a limit in how high you can go in the frequency before that blocking limits you.
Oh, and a third issue: if 30us are already too much time, I can't really write "heavy" code (one of the reasons why I haven't touched SD cards and file systems; there may be blocking operations...).

So far for the status quo. I've had a lot of thoughts for how to solve this, including Netzpfuschers suggestion to switch to FreeRTOS. However, FreeRTOS can't solve the blocking and is by far not fast/efficient enough to handle the signal generation via tasks. From all I could find it operates with >=1 millisecond of resolution which is not suitable at all if 30us jitter/delay are already too much. It may make some things easier but it won't solve this issue.
Another idea was to somehow limit the processing to the time after an ontime where it would be the least likely to delay another ontime. However, that doesn't work anymore as soon as you have more than one note.
I also tried to enforce the output generation via fast, periodic interrupts, and that failed greatly. Either the frequency is so low that it sounds like crap, or it is so high that I'm running out of CPU time.

For a while now I've been thinking that buffering is pretty much the only reasonable option. Over the last few weeks I've been working on a buffered solution and now I can say with some confidence that it looks very good. At first I tried to implement ping pong buffers but that didn't quite work. Therefore I switched to one FIFO buffer which works very well so far. When previously the jitter was in the order of tens of microseconds (and well audible), it is now in the tens of nanoseconds range - or in other words: it couldn't be any better. Not only is the jitter gone, sysex processing doesn't cause stuttering anymore either. Currently I'm buffering for 5ms which should be short enough to not be audible. The buffer time will be adjustable through sysex.
Btw: someone mentioned that buffering will take more CPU time than the previous real time solution. And he's absolutely right. The signal generation part is easily twice as complex now. However, I'm nowhere near stressing out the CPU - or in other words, buffering frees up more CPU time than it eats away.

While this is great (and long overdue), there are still issues and glitches I need to track down. I can't tell you when I can release it but the current progress shows that it's feasible so it will be released one day...


Kind regards,
Max

Offline Georgios

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Re: Syntherrupter - A Feature-rich, Polyphonic Interrupter
« Reply #165 on: July 13, 2021, 07:38:44 PM »
3 Coils

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Re: Syntherrupter - A Feature-rich, Polyphonic Interrupter
« Reply #165 on: July 13, 2021, 07:38:44 PM »

 


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