PreenFM > preenfm2 and preenfm3
PreenFM2 SMD version
SirPrimalform:
While I have no need of another PreenFM2, I definitely want to see how the build comes out.
zelea2:
I've got the majority of the components from China so today I've started the new schematic and PCB.
I still need to simulate the analog chain and probably remove/change some of the passive to make it comply with
the DAC's requirements and get a 0dBu (0.775V) signal output.
I'm documenting the progress here https://uglyduck.ath.cx/ep/archive/2017/11/PreenFM2_SMD_Version.html
I've listed there what I think are improvements from the current schematic.
The STM32 still has a lot of free pins. I could even get rid of the MCP23S17 and connect all the switches and encoders directly to the ARM uP.
I've added a second serial interface to connect maybe with another PreenFM2 or sync to other devices.
Before routing the PCB I'd like to ask the owners of this synth what do you miss in your PreenFM2?
What else can be added to make it better?
Some silly ideas:
- RGB LEDs or NeoPixels
- MIDI Through
- I2C OLED displays
- capacitive switches or sliders
- a stereo amplifier and socket for headphones
lokki:
a stereo out jack and a dedicated headphone out would sure be great. other than that i am pretty happy. i would wish there were 4 outputs instead of only stereo so that you could route each instrument to another channel. but that is not gonna happen without adjusting quite a lot of the firmware and i am also not sure if the stm32 would support another stereo dac for the additional outs.
zelea2:
--- Quote from: lokki on November 15, 2017, 10:02:25 AM ---i would wish there were 4 outputs instead of only stereo so that you could route each instrument to another channel. but that is not gonna happen without adjusting quite a lot of the firmware and i am also not sure if the stm32 would support another stereo dac for the additional outs.
--- End quote ---
The STM32F4 has two I2S interfaces and the PCM5102 are cheap and in small packages. One problem is the size of the 6.3mm sockets; there is not enough room for 4 of them so I'll have to switch to two 6.3mm stereo sockets instead. But as you said the main problem is the firmware support.
Xavier, do you think the design I'm doing will be of any interest? I will publish a diff file with the changes of the git firmware (mainly using #ifdef's for the differences). Should I bother to ground one currently unused STM32 pin so the future firmwares could distinguish between my hardware design and yours?
This will be just to report on the LCD that you are not using the correct firmware for the board and stop the code from running.
lokki:
two stereo jacks would be awesome...
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