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Author Topic: PiDSP - 24bit/196KHz DSP board for Raspberry Pi  (Read 3032 times)

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Offline Pitrsek

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PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« on: April 09, 2017, 06:29:14 AM »
Hi guys and gals,
I've been reading this forum(and watching Dave's vidos)for some time, today I've decided to join.
Coincidentally, today I've also migrated my hobby project to a github. So I tough I'll share it with you:
https://github.com/freeDSP/PiDSP
So if you feel like it, take a look, tell me what you think.

Thx for your feedback,
Pitrsek

 
 
The following users thanked this post: diyaudio, bobaruni

Offline Pitrsek

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Re: PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« Reply #1 on: April 09, 2017, 07:47:22 PM »
Some pictures:
 

Offline Pitrsek

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5V buck fix
« Reply #2 on: April 15, 2017, 12:52:13 AM »
Fixing the stuff I missed on last revisions(there is a buglist on github)
One of the more shameful mistakes was thermal design of main 5V buck. It could not deliver 3A with temperatures I would consider reasonable.
I kinda did not pay enough attention to small print in the datasheet  |O. Go and take look at PCB that is used for specifying package thermal resistance, that PCB is bigger than you would expect... 
I sandwiched buck between edge of pcb and RPI connector. I missed my goal of 3A output by about half an amp. Also I did not verified used inductor beforehand, AC losses were way to high. So for next revision I've improved thermal design for buck and diode. Since I have a little more board estate I can go for a bigger inductor. Samples are on the way(WE 74437358047). And I'll test the inductor before  sending boards to production.

I've also discovered that I did not performed "remove unused pad shapes", so there was not really much copper in the ground plane in between RPI connector. That compromised heat transfer into the rest of the board. That is fixed now, so hopefully we'll get better cooling. I'll probably go for 35um copper thickness on next PCB as well - to see the effect of changes. As you can see the difference in web width is quite big - actually now its more than twice the original width.
 

Offline Pitrsek

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Re: PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« Reply #3 on: April 18, 2017, 12:09:02 AM »
?Still some stuff to clean-up, but PCB is starting to look quite all-right  :)
 

Offline Pitrsek

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rotary encoder recommendation wanted
« Reply #4 on: April 20, 2017, 05:06:09 AM »
Hi,
I'm looking for a quality rotary encoder with switch, any recommendation? It's going to be used as front panel controls, so it will get decent amount of (ab)use.
Optical encoders seems to be a bit too expensive for my taste.
Also new inductors arrived today, I should have impedance measurements tomorrow.
 
EDIT:Found rotary encoder thread :) http://www.eevblog.com/forum/projects/decent-rotary-encoders/msg949756/#msg949756 
« Last Edit: April 20, 2017, 05:12:52 AM by Pitrsek »
 

Offline bobaruni

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Re: PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« Reply #5 on: April 23, 2017, 02:42:49 AM »
Well I think your part of it looks really nice, very nice board design too.
I'm using the same cheap ES9018 DAC board from Ebay and some parts of it are implemented badly and my board (not saying all sellers sell the same) had a lot of bugs with it that made it sound terrible.
Silly mistakes like regulator transistor PNP instead of NPN and inserted backwards and ES9018 running on 5V instead of 3.3V
The I/V leaves a lot to be desired as well but I have modified it to use a similar I/V to that on the ES9018 datasheet and it now sounds fantastic (no more clipping and clean transients).
« Last Edit: April 23, 2017, 02:50:02 AM by bobaruni »
 

Offline diyaudio

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Re: PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« Reply #6 on: April 24, 2017, 08:45:17 PM »
Hi guys and gals,
I've been reading this forum(and watching Dave's vidos)for some time, today I've decided to join.
Coincidentally, today I've also migrated my hobby project to a github. So I tough I'll share it with you:
https://github.com/freeDSP/PiDSP
So if you feel like it, take a look, tell me what you think.

Thx for your feedback,
Pitrsek


 
Very nice project. keep us posted please! 
 

Offline pieman103021

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Re: PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« Reply #7 on: April 24, 2017, 10:47:16 PM »
Really interesting project, looking forward to seeing it progress.
Exclamation Point!
 

Offline Pitrsek

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Re: PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« Reply #8 on: April 25, 2017, 08:40:14 AM »
Thx for kind words. I've measured samples of new inductors.
?It turned out that new inductors are not really better than old one(SRP6540-3R3). At least comparing real part of impedance (the part that is responsible for losses). One of the WE part is 4.7uH instead of 3.3uH. WE design tool was quite certain that I can get away with it. We'll see :)
They may be cooler than the original part, due to having bigger size/better cooling ability. Measuring C/W is next on the list + in circuit testing.

I'm leaving for OMICRON Lab Power Analysis & Design Symposium tomorrow. Last year was rather nice, hopefully this year will be even better. Then I'll be off for some traveling on weekend. So no more updates from me for rest of the week.

Mjjg from DiyAudio has received his PiDSP, so he can continue with linux driver development. Also one of my friend is joining in on driver development. So driver team is twice the size of HW team :)

Oh, and I've ordered enclosure and started working on the front panel design.

And that would be all for today.

P.S.: I'm still looking for quality mechanical rotary encoder with smooth action. I've tested just few, but so far it seems that optical ones are in different league. The feel of optical encoder is really nice...
 

Offline Pitrsek

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Re: PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« Reply #9 on: May 19, 2017, 02:52:58 AM »
Hi,
thx to my friend(thank you Honza) and his LabView skills I was able to do some crude C/W testing of the inductors. Test were rather rough - no climatic chamber/box, just a programmable power supply and constant power script in LabView. The winner is 7443340330?(not on pictures), with  cca 7.25C/W. The original part has C/W roughly twice as big.  I have the new part soldered on one of blue boards and ready for some more testing :)
Layout is almost done, I'm going trough DRC checks and pondering about some footprint updates. Also two variants of rotary encoders are on the way - one from bourns, one from Alps.
Question for you guys (and gals.) ), do you like dents for volume control?

Take care,
Pitrsek
 

Offline Pitrsek

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Re: PiDSP - 24bit/196KHz DSP board for Raspberry Pi
« Reply #10 on: June 13, 2017, 06:51:33 AM »
Hi,
With B2 revision, there was no provision for powering down the expansion boards(ADC/DAC etc.), which is pity. For B3 revision I've designed simple high side switch. Before I close the pcb design, I just wanted to test the switch, so I lets have some test-boards. Second board is new and better power sequencing - resetting diodes and some minor tweaks. Again, just testing before using it in the the new revision.

Also we will have a AMA on 13.06. So if you feel like, please stop by!
https://www.reddit.com/r/diysound/wiki/ama
 
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