Let's Design and Build a (mostly) Digital Theremin!

Posted: 6/22/2021 11:01:46 AM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

DAC Chip

A little bird tells me that the DAC IC on that board I just bought is MS8416T.  At Mouser I see CS8416-CSZ for the human solderable package.  A $10 chip! 

Datasheet: https://statics.cirrus.com/pubs/proDatasheet/CS8416_F3.pdf

As I had guessed, the SPDIF input pins can take full digital levels (through a 0.01uF cap).  I don't see anything in the way of troublesome muting scenarios, and there doesn't appear to be any auto switching of input sources (there are 4) hence the front panel slide switch.  There is clock auto switching if the PLL goes out of lock that requires a power cycle, though this can be disabled by grounding the external clock input.

I ordered 6 more of the boxes: https://www.amazon.com/gp/product/B088R259SW.  Guess I snagged the last ones for a while.

Interesting what shows up on eBay when searching for "MS8416": https://www.ebay.com/itm/233928455517

Searching for CS8416 is more fruitful:
https://www.ebay.com/itm/393398253078
https://www.ebay.com/itm/373156849424

Posted: 6/22/2021 12:31:40 PM
Mr_Dham

From: Occitanie

Joined: 3/4/2012

Delicate question that this DAC...

Make or buy, independent box or integrated PCB, ship or advise user to source one, ...

No strong preconceived ideas but i think that Out-Of-Box-Experience is the right focus. 

*   "DAC integrated PCB" option means that you want that D-Lev apear as a classical "analogue" sound device with phoneJack output. It is quite straight forward but you loose the advantages of numeric connection.

*   "DAC box" option means that you totally assume that D-Lev is a digital Theremin and as such its output is digital. Then you might provide (or just suggest) a DAC box just to avoid frustration for user who don't have it.

Two different approach for the same question: how to bring the sound to users' ears ? 

Posted: 6/23/2021 2:29:01 AM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

"... i think that Out-Of-Box-Experience is the right focus." Mr_Dham

I think so too, which is why I think it's important to make the kit as turn-key as possible.  Though for some international folks the $10 box could cost them so much in shipping that it perhaps isn't worth the convenience?  (It's weird that the world is still so divided.)

Posted: 6/23/2021 10:08:47 AM
Buggins

From: Porto, Portugal

Joined: 3/16/2017


*  "DAC integrated PCB" option means that you want that D-Lev apear as a classical "analogue" sound device with phoneJack output. It is quite straight forward but you loose the advantages of numeric connection.

*  "DAC box" option means that you totally assume that D-Lev is a digital Theremin and as such its output is digital. Then you might provide (or just suggest) a DAC box just to avoid frustration for user who don't have it.

Why not combine?
Integrated DAC (or DAC/ADC/HP/Mic codec) for analog I/O.
S/PDIF for digital I/O.

Posted: 6/23/2021 5:44:25 PM
Mr_Dham

From: Occitanie

Joined: 3/4/2012


I think so too, which is why I think it's important to make the kit as turn-key as possible.  Though for some international folks the $10 box could cost them so much in shipping that it perhaps isn't worth the convenience?  (It's weird that the world is still so divided.)


Yes, shipping the DAC's 10 cm cubic package around the world is not so much cost effective.
Also, Europeans (like me) may prefer sourcing one with a proper power outlet.

So, you might want to make it optional. But then you need to know how much you want to have different selectable options (DAC, box, etc...) and how much you want to handle different Bills Of Material.  I know by experience that it is not so easy...


Why not combine?

Of course it is the king's choice, but I imagine it requires some more devlopment and creates some additionnal cost compared to a 10$ box...

(Creating a small PCB prod, it would be hard to compete with a 10$ price).

Posted: 6/23/2021 10:43:31 PM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

Look Ma, No Vias!

Spent all day (12 hours minus chow times meal prep) on the tuner driver board (ass is sore from sitting so long, eyes dry from staring into the abyss):

A schematic mistake cost me 4 hours at least.  But this is actually kinda fun in an extremely tedious sort of way!  Like playing in OpenSCAD...

PWB layout is a fiddlers dream - you have to draw the line at some point and say it's done.  The trick for this board was to orient the tops of the ICs towards the regulated 3.3V, which created the copper fill island you see above.  The other trick was to rotate J2 180 degrees.  J3 is there in case I want to light up the decimal point on the 7 segment display.

For the life of me I don't know why I didn't do this years ago, it's pretty painless.  At long last, I'm finally an EE, got the PWB merit badge and everything.

Posted: 6/24/2021 12:01:12 AM
pitts8rh

From: Minnesota USA

Joined: 11/27/2015

For the life of me I don't know why I didn't do this years ago, it's pretty painless. - Dewster

No kidding.  I avoided it for years because my company had dedicated people to do layout for us, and from what I saw it was not trivial to learn. But then this hobby stuff doesn't exactly push the limits for complexity and density.

Alas, if you had only taken this on a little earlier I could have avoided the Diptrace commercial license upgrade...

Posted: 6/24/2021 2:45:50 AM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

"I avoided it for years because my company had dedicated people to do layout for us, and from what I saw it was not trivial to learn."  - pitts8rh

Same here.  The formality of it all is what kept me away from picking it up.  Having those folks around actually burned me pretty bad on my first board, I didn't know what I (and they!) didn't know, and I found it weird to be asking / ordering others to do stuff.  We had a couple of engineers in our department who took the bull by the horns, I should have too.  Though both in college and at work everyone did layout on X terminals, which was an entire clunky ecosystem that I never entirely adapted to (editing config files to get the backspace key to work...).

"Alas, if you had only taken this on a little earlier I could have avoided the Diptrace commercial license upgrade.."

I feel pretty bad about that, though your layouts, dimensions, and interconnect assignments (not to mention actual boards!) have given this project a real leg up, which I really, really appreciate!  Both you and Vadim have inspired this old man to learn a few new tricks.  It's tough getting it up for new software / whole new fields.  You guys are so adventurous!

Having done three fairly trivial boards now, it seems the way to approach layout in KiCad is to get everything arranged and throw down some crap connect, rinse & repeat.  KiCad doesn't let you easily rip up a trace one segment at a time (why not?) but it does have a fairly powerful interactive editing mode (Route | Interactive Router Settings... | Mouse drag behavior | Interactive drag) that should be the default because it lets you nudge things to the point where you're actually doing layout from whatever wire bits and pieces you have there.  If I hadn't stumbled across that I'd probably still be laying out my first board.  KiCad's schematic editor is pretty garbage though, at least 2 steps down from LTSpice if you can imagine that.  And since you need a schematic to get into layout, everyone's initial experience is that.  If it weren't for on-line tutorials I don't think I'd have had it in me to tackle either KiCad nor OpenSCAD.

I must say too that just laying out an oscillator on pad per hole vector board takes me much of a day to plan out, and several more hours to realize with solder and bus wire, so this isn't all that much extra time, and then it's done for good and it can be trivially replicated.  And I guess I'd always rather be pushing a mouse than doing real work.

Posted: 6/25/2021 7:27:26 PM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

AFE (Analog Front End)

I wanted to understand KiCad a little better before tackling the AFE.  The tuner display boards were pretty easy, the tuner driver board more involved, and yesterday I did the 4x encoder board and began the AFE.  Today I think the AFE is finished:

Studied a capacitance paper to do as Roger cleverly did on his AFE, which was to use the FR4 PC board material as a dielectric, with pads on the front and back as capacitor plates.  This gets you around the need for high voltage 1pF capacitors, which can be hard to source as the value is so tiny.  Turns out 4mm square at 1.5mm separation gives you ~1pF, which is TP4 above.  It also turns out that 3mm diameter gives you ~0.5pF, which are TP5 and TP6 above, which one would connect with a solder blob bridge if so desired.  This gives some tuning elbow room / future proofing.  The ground and power plane copper fill are trimmed back from the high impedance area so as not to add even more fringing / padding.  The coil connects across single pins on the right - J3 (drive) and J2 (sense) - tack soldering the coil wires here seems to work OK.

I'm learning to plop everything down anywhere, roughly locate the board mounting holes, create large copper fill planes, and then see what is really left over in terms of connectivity.  Then shove stuff around until the connectivity gets simple / makes the most sense.  Then move everything to the origin, add the board outline, do final placement, and start wiring.  The 3D view is super useful for checking the copper fill, which can be quite critical on a 2 layer board (oh to have dedicated power and ground planes, and two perpendicular layers: wiring would be a snap).

Now on to the Main board that connects everything together.

Posted: 6/27/2021 8:41:36 PM
dewster

From: Northern NJ, USA

Joined: 2/17/2012

User Manual

Just posted a preliminary user's manual for the D-Lev:

https://d-lev.com/support/D-Lev_Manual_2021-06-27.pdf

The quick reference has been updated too:

https://d-lev.com/support/D-Lev_UI_Quick_Reference_2021-06-27.pdf

Roger helped me a ton with the editing of the manual!  (Though I am definitely to blame for any mistakes!)

I don't know why, but the existence of a manual makes the D-Lev feel like more of a real "thing".

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