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Open Hardware DSP Platform
Open Hardware DSP Platform
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Old 15th February 2016, 11:37 AM   #1
ohdsp is offline ohdsp
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Default Open Hardware DSP Platform

Hi everyone,

A while back I had started playing with some digital signal processing stuff, had been looking at FreeDSP and a similar project in Elektor, neither offered what I wanted and the MiniDSP seemed the simpler option to get working with initially.

I did start playing around with designs for a more powerful/complex DSP board about a year ago (raspberry pi hat type board: https://github.com/pwzj/ohdsp), never finished it in that form though. And then I also picked up on the FreeDSP V2 thread. Again what was being designed (at the time) wasn't quite what I was after and I shifted my focus to designing a set of modular boards I could play with (but not bothering to link in a Pi or any other small board computer).

Anyway I have real boards I am building up and stuck some design files and a website up: Open Hardware DSP Platform

This is not designed to be a rip off or clone of any other work but as I have completed PCB designs and actually have real hardware I am building up now it would seem a waste not to make it available for others.

All hardware designs are under the TAPR open hardware license. PCBs/Schematics are in KiCad. I don't sell PCBs or hardware or anything for this, the website is information only at the moment.


Cheers.
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Old 15th February 2016, 09:28 PM   #2
doctormord is offline doctormord  Germany
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Congrats to the project and for using KiCAD.

You may want to overlook the pcb images on your website, which are quite "huge" pngs. (600kb)

I'll attach the shrunken down files.
Attached Images
File Type: png 2453515_orig.png (80.6 KB, 739 views)
File Type: png 5832289_orig.png (97.9 KB, 737 views)
File Type: png 758901_orig.png (64.7 KB, 721 views)
File Type: png 8978959_orig.png (68.0 KB, 717 views)
File Type: png 4654162_orig.png (59.9 KB, 713 views)

Last edited by doctormord; 15th February 2016 at 09:39 PM.
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Old 15th February 2016, 10:00 PM   #3
ohdsp is offline ohdsp
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Thanks doctormord,

Think I just grabbed the images off DirtyPCB when I placed an order, didn't really pay attention to the image size!

Wanted to upload some real photos instead when I finish populating boards, if I can get some decent photos.
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Old 16th February 2016, 07:55 PM   #4
golfgtig60 is offline golfgtig60  Italy
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it's a very good project..
It's work?
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Old 16th February 2016, 09:14 PM   #5
ohdsp is offline ohdsp
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I'm am building up a number of these boards by hand at the moment. I have worked with some of the parts in the past without any problems. Assuming I haven't made any silly mistakes there is no reason for any major issues (famous last words though...)
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Old 23rd February 2016, 04:21 PM   #6
lindamar is offline lindamar  Spain
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Super project and congratulations !!

I am also following the freedsp V2 thread which is also very interesting. I love the idea of you sharing and opening all your designs for us to learn and discuss. Sincerely, thank you.

On a more operational note, I have done some smd soldering in the past with different results, to the point that I am considering building a diy oven to make things easier. My eye are not what they use to be, even with a magnifier. How is your experience with the ADAU1452 and your boards ? Any recommendation for manufacturing ? (site...)

cheers
Pepe
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Old 23rd February 2016, 10:30 PM   #7
ohdsp is offline ohdsp
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An SMD toaster oven may be a good investment if you fancy doing a lot of boards. I have been building up 8 of these boards (3 DAC, 3 DSP, 1 ADC, 1 PSU) and there are a lot of SMD parts...

Soldering the ADAU1452 was ok, I put a large (3mm) via in the centre pad, fixed the chip around the sides and soldered up through the centre, 2 boards are fine although the 3rd looks like it may not have flowed as well as it should have, but that was just me being unsure having not used this method before.

I have boards up and running now. Feeding the ADAU1452 from a SPDIF output and into the ADAU1966. I have connected a headphone amplifier to the positive outputs of channel 1 and 2 on the DAC (only passive filters). The ADAU1966 sounds very good. Very very good in fact, given its a 16 channel dac chip for less than 8. It is also seems happy driving long spindly unbalanced phono cables with no buffering.

I have not tested everything yet but this is a good start! And a good sounding start at that as well.

Here is a (bad) video of my test setup running on a bench supply, on some stupidly small table.... I do now have it running off of the real supply as well:

https://goo.gl/photos/qqrevPUD3Sfw4fRK8

All I need now is a decent workshop area I could setup in...
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Old 24th February 2016, 07:13 AM   #8
ojg is online now ojg
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Hi ohdsp,

I really like your boards and I really like the "competition" between you and freeDSP, finally there is some momentum on the DIY DSP front.

I am curious about your soldering of the ADAU1452, are you saying that you were able to solder this using just a soldering iron? And not stencil, paste and toaster-oven? If so, you should consider making a video on how you did that, that would be very interesting.

Br,
OJG
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Old 24th February 2016, 09:40 AM   #9
ohdsp is offline ohdsp
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Yes I did solder it by hand with a fairly large soldering iron bit, although on a cheap temperature controlled station. I can have a look at making a video on how I soldered the chip, but this may not happen for a couple of weeks as the parts I have would need baking. That is where a toaster oven would come in handy! Ideally the parts and boards should go through a preheat stage. I figured parts have been soldered by hand for many years without issue. If it works using my crude method then any form of reflow (air gun) or oven methods should work well if you stick within the temperature and time specified in the datasheet. If you can get free samples of the parts from Analog then the risk isn't so high.


Also on Pepe's question about manufacturers I used DirtyPCB for all my boards in 1 batch.

The 4 layer board is designed for a 0.2mm prepreg, 1.2mm core, 0.2mm prepreg stackup (core could be any thickness though). Boards are not impedance controlled but traces to IDC connectors are designed to have a ballpark figure to match with 26AWG ribbon cable driven in signal-ground-signal-ground config (but not 28AWG as I could not match that). The traces are quite thin (0.135mm/5.3mil) but a lot of manufacturers now support down to 0.127mm/5mil as standard. I would recommend DirtyPCB for the 4 layer board.

The 2 layer boards can be from anywhere, really does not matter. Traces are 0.3mm/11.8mil or thicker and the PCB thickness is 1.6mm as normal.

The boards I have are generally very good. Some silkscreen and a couple of holes not quite lined up 100%, also they sent 12 4-layer boards but 2 of them have the via's not seated in the board properly (copper sitting proud) which ruins the ADAU1452 footprint, but I did get what I ordered in usable boards.

There are mistakes on Release 1.0 boards but they do work, I will work on 1.1 boards with all the mistakes fixed and some minor tweaks to things like connector hole sizes.

Cheers.
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Old 27th February 2016, 02:02 PM   #10
ohdsp is offline ohdsp
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I put a little update on my blog that has some pictures of the boards I have up and running:

Open Hardware DSP Platform - Blog

But just so you can see my test setup:
Whole_setup_midsize.jpg
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