Topics

1

preenfm2 and preenfm3 / LCD display connector

« on: February 02, 2018, 04:10:54 AM »

I was looking into building some cases for my PreenFM2s and I don't know how to solve the problem of the LCD display height. Now I have a normal ".1 header male and female and that's quite high. Even if I replace it with the Augat type (see picture) I'll only be able to lower it about 1mm and it needs to be flush with the buttons and that's 8-9mm lower. The only option I see is to solder the LCD header permanently to the main board.

I could raise the buttons (by using a different cap or by gluing 2 caps above each other but I can't raise them too much because they are limited by the encoder knobs.

How did you solved this problem. Are your LCDs much thinner than mine?

2

preenfm2 and preenfm3 / priority bits

« on: February 01, 2018, 01:39:26 AM »

In the git code I've noticed that __NVIC_PRIO_BITS is not defined so it stays at its default value of 4
This means 4 bits for the PreemptionPriority and none for the SubPriority

Then in various places in the code both ChannelPreemptionPriority and ChannelSubPriority are
initialized with non zero values. Obviously the ChannelSubPriority has no effect and stays at zero.

One only needs sub-priority when several interrupts with the same preemption are pending then the
sub-priority decides which one is served first.

3

preenfm2 and preenfm3 / PreenFM2 encoders

« on: January 23, 2018, 08:22:56 AM »

Since I don't have a PreenFM2, I don't know what to expect as behaviour for the rotary encoders. Can someone please let me know how responsive they are?

The best I've obtained on my PreenFM2 version is about 4 steps per second with reliable detection and no back-skips. I've improved my detection as much as I could and the software is supposed to catch up to 25 steps per second but I don't think these encoders can handle that kind of speed (at least the ones that I have).

Is 4 steps per second acceptable or are your encoders better?

4

preenfm2 and preenfm3 / VolcaFM as development platform for PreenFM

« on: January 16, 2018, 08:48:33 AM »

I am in the process of adding note velocity on my VolcaFM and while I was reversing the schematics I couldn't stop noticing similarities with a PreenFM2.
MIDI Keys Velocity for Korg VolcaFM

Both devices use an ARM Cortex-M4 so the PreenFM2 firmware could be ported (in theory) to a VolcaFM. Of course the original code will be lost
forever. The Volca uses a companion processor to read the touch keys and the protocol could be quickly reversed by hooking a logic analyzer on the SPI connector. The Volca doesn't have a nice screen, only a 9x7-segment display and neither it has the USB connectivity or pen drive interface. Instead is has a stereo 24-bit DAC.

What do you think; is it worth the effort to port this firmware to a Volca?
The Volca's firmware can be updated via an audio file played from the computer. I'll have a look in the future to see if that can be reversed so we could save the original firmware. Or maybe they've forgotten to fuse protect their Spansion FM4 processor.

5

preenfm2 and preenfm3 / PreenFM2 SMD version

« 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.

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.

6

preenfm2 and preenfm3 / Schematics library

« on: October 28, 2017, 01:34:51 AM »

Hi Xavier,

Would you mind checking the missing "special" Kicad library in git? The schematics looks broken and with missing symbols when I try to load it in Kicad.

Thanks.