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PreenFM2 SMD version

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zelea2:
I'm in the process of redesigning a SMD version of PreenFM2.
The original goal of this design was probably to make it as easy as possible for people to solder their own kit.
Unfortunately  the Cerb40 module cannot be bought anymore so someone else has to solder the LQFP64.

I plan to build 5 pieces of this new design and make it as cheap as possible. The majority of components
will be bought from Aliexpress and the rest from Farnell.
- there will be just one PCB (15x10cm), no sockets.
- the 2 shift registers replaced with MCP23S17 (port expander)
- the 2 DACs replaced with PCM5102A
- OpAmp replaced with OPA2337
- extra MiniUSB socket placed on the main board
- all resistors and caps as SMD 0603
- cheap LCD 40x4 (no OLED)
I believe the total BOM will be well below 100$ (without the case)
The changes to the firmware to accomodate the new DAC and SPI-expander will be trivial and made with #ifdefs

Since I'm not comfortable with this KiCAD tool I have switched to OrCAD+Specctra and I'll make all design files available.
So far I've been able to export the PCB as GenCAD and after a lot of massaging I've now got an OrCAD PCB of the current
design with SMD passives. This way all the sizes and encoders/switches position will be preserved and I'll be able to use
the same cases.

Xavier:

--- Quote from: zelea2 on October 31, 2017, 07:23:02 PM ---I'm in the process of redesigning a SMD version of PreenFM2.
The original goal of this design was probably to make it as easy as possible for people to solder their own kit.
Unfortunately  the Cerb40 module cannot be bought anymore so someone else has to solder the LQFP64.

--- End quote ---

Yes, the goal is to have a fun DIY synth project.
The preenF405 (CERB40 design adapted for the preenfm2) is and will remain available. So nobody has to solder the LQFP64 STM32 if they don't want to.

I don't get what you plan to sell ? the components ? Presoldered SMD preenfm2 ?

The move to OrCAD will move this project away from hobbyist.

Xavier

solipsvs:
exciting!  can fit easier into euro rack maybe?   :)

zelea2:

--- Quote from: Xavier on November 01, 2017, 09:52:47 AM ---
I don't get what you plan to sell ? the components ? Presoldered SMD preenfm2 ?

The move to OrCAD will move this project away from hobbyist.


--- End quote ---

I completely agree with you about OrCAD. I'm also in favor of open source and I've been using Linux and free software for the past 20 years.
Unfortunately KiCAD is completely new for me while in OrCAD I've built over 100 boards. Initially I've planed to use KiCAD+Specctra but since
I need to migrate your design to KiCADv4 to maintain the schematic/PCB relation it's almost as much work as doing it from scratch.
Anyways I'll export the final PCB as GenCAD and MIN formats to make it as accessible as possible. Mentor PCAD can also load OrCAD files.

I am an electronics engineer by trade and I design ICs for a living; I also do some board design occasionally. I just want to experiment with
FM synthesis and since I already own too many keyboard synthesizers I was looking for a modular one. I've tried to get a Yamaha DX200 but
they are so rare and expensive. The PreenFM2 seems a very capable choice and I like this idea more than a VolcaFM. Music for me is just a
hobby and I'm in my 4th year of taking piano lessons ;-)

I couldn't get a PreenFM2 kit since they are out of stock so the next best thing is to build my own. Yesterday I've bough all the components
from Aliexpress, including the STM32 (5$) and the LCDs (5$), rotary encoders and switches and I've paid only 150$ for five kits. The prototype
PCBs will be some 40$ for 5pcs 2 layer 15x10cm size. So in the end the whole BOM for this project excluding the case will be less than 50$/unit.
That's how insanely cheap you can spend to build your own PreenFM2. The drawback is that now I have to wait 3-4 weeks for all the
component to arrive from China and probably as much time for the PCBs because I won't send it out before having all the components in
my hand to validate the footprints. For the cases I haven't decided yet - either I'll use a laser cut service and translucent green acrylic or I'll just
buy 1mm anodized aluminum sheets and machine it on my KosyA5 CNC router. I only plan to build these 5 units and maybe sell 3 or keep them all.

Attached are some pictures of my synth's room ...

solipsvs:
id love one if youre taking pre orders!

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