Multichannel Audio DSP Field Mixer Recorder

excited about my new smaller thinner preamp cards using 1.27mm headers.
so far they seam to work as before. I kept some space by the optical relay as I expect there to be more front end circuitry. I hope to find a smaller 1 form c opto relay to use. found a toshiba that looks promising that's 1/4 of the size. The 60v 1Amp clamping protection diodes have started to loo very large so working on finding some smaller diodes to.  the gold caps to the right are DC blocking caps before the ADC. The PGA2500's output some DC which needs filtering out.

The dual rail cards are quite long at 80mm but output +/- 1 amp at incredible low noise using lm43602's and TI ultra low noise regulators.
I have 1 card for +/-5v and one for +/-15v ( or I might use +/- 9v )  depending
on how much power I want on the master outputs of the line drivers.
I should change the conductors for +/- 15v setup from 6.8uH to 15uH.
The negative rails needs a lower in series resistance inductor 150megOhms. the + rail works with 75megOhms.
both cards are set to  run at 1mhz switch frequency but are not running in sync yet.
I'm interested in knowing how you can use an ADC on say the ARM micro to monitor the DCV of each power channel and then even using a digipot fine tune the accuracy of each rail. fine tuning the Voltage is perhaps overkill but monitoring the rails could be good way to self test the power is healthy before potentially frying amp chips in case a power card went down. maybe i'd need to use a higher voltage capable adc to feed the results to the micro ? and how about the negative voltages? would I need an ADC capable of neg voltage ? or use a voltage buffer for each channel and invert the neg rail?

Although I was fairly happy with the shrinking down of the 1st cards ( still more to do ) the 3.3v 2amp power card was a complete fail!!!

1st I messed up the voltage divider traces. I tried adding the correct resistor to ground to set the TI tpsm84209 output voltage to 3.3v

Without the regulator IC in circuit the output fluctuates all over the place.

I'm thinking so far using the through hole resistor made the voltage divider loop to large. ( the datasheet warns against making that loop large ! )

Although the caps are within voltage spec I'm not sure about the in series resistance. This is were to be honest I'm entering a new area. I don't have a LCR meter and I don't even know if there is LCR mode on my keysight 34461A bench meter. ( better check the manual but dont think so ) 

maybe if I generate 100khz square wave with the mixer recorder I could get the in series resistance of the capacitors I used that way ( the old mixer recorder prototype is still working ) . never used an LCR , no idea yet how it works. looks like I'll need one eventually.

Even the picture I took of this little 1 x 1 cm board failed. it came out upside down and blurred. it cost 1$ , so I think the best thing is to make a better effort with the pcb design and start from there!

These 4 cards will slot into a backplane to make

+/-15v(+/-1A) line drivers and headphone

+/-5v(+/-1A) preamps and adc + dacs

48v(135mA) phantom power

3.3v(2A) digital power

I just finished soldering up a smaller modular phantom power board.

I did look into making the 12v -> 48v boost converter side without IC's ( discrete components ) but it would have been to large for what I need. I tested on a dummy load and can produce 134mA 47.5V without the board warming up over long periods.

I've started to use thinner circuit boards now to to reduce weight. I should have used 1.27mm headers for this board. I went against it thinking its a power board but at maximum 134mA a smaller header would have been fine.

This is just the start of shrinking all my proto boards down !

Next is the dual +/-5v and +/-15v boards and new smaller preamp boards with end cutouts for the DC blocking caps :)

DMA is working from SAI interfaces -> memory & memory -> uSD cards for recording and playback.

I have UART / bluetooth RX TX working over DMA to.

I'm not using DMA for SPI or both I2C1 and I2C2 buses.

I might need to for the I2C readback from DSP if I start reading a lot of meters and LTC timecode etc.

I'm thinking I will make one large packet from all meter data. its 1 byte per meter with a few bytes for header info for each meter type. I think I can get all the useful data back to the android app in approx 45bytes per packet streaming at about 1kbps. 

The main problem seams to be the app inventor app can't keep up with the speed of the packets being sent from the field recorder. I did slow down the TX rate so it could also be the way the individual screens are cleared.

I have to say a massive thanks to ABG on the MIT app inventor forum for helping me figure out a fast way to receive the 10 byte packets. My caveman code in app inventor was just not working quick enough :)

https://groups.google.com/forum/?utm_medium=email&utm_source=footer#!msg/mitappinventortest/C2KYLiD1k0g/w_nyJ6OLAgAJ

I thought my adaption of ABG 's example code was working at the end of the thread but I was wrong. I had to slow down the packet stream from the ARM since it was just way to fast.

I'll hopefully be able to clean up the glitches and move on from android app designer. Not my thing !!! If the gain peek metering works I will add metering to main faders and mix faders. There will also be a screen with all faders working at once!! if its fast enough !

I think I need to switch my BT dongle to BTLE 4. I read its better at streaming data.

need to start on the realtime audio meters soon...

24bit and 16bit switching playing and recording / different channel counts.

I think I need to freeze the DSP while changing these rates but working well without !! 

no clicking noise on change over either :)

Maybe a bit pointless but it helps a little bit with knowing if i'm record or playback mode and I can report what bit depth / FS audio

mode i'm in when I get that working :) but this is a BT only field recorder !!! :)

OK starting properly now.

The CS4385 has to get going within 10ms so I start this 1st after reset high , rather than having it wait around for the ADC

to initialize. I'd set rest high on ADC DAC then DSP and left the DAC waiting or the ADC to startup.

THINGS TO DO LIST...

check over SAI configs and DMA for playback / record slots and make sure recording / playback works on both hardware slots

dual recording to cards , have set up DMA but how to write to both card at same time.

recording armed tracks from TDM8 from BT app  ( not changing TDM mode , just recording slots from it ! ? )

recording both ADC DAC cards at the same time ? up to 16 channels wav poly or separate mono !!

playback of different track count from wav poly? just assign to playback slots in order recorder ? 

LTC timecode intergration into file recording. LTC timecode at start into wav header ?

NEW analouge board with OVR lines for analogue limiter on front end needed. ( old 4 channel analouge board needs updating ) 

power cards , dual +-5v , dual +-12v, phantom pwr to slot into new analouge board.

some kind of master 12v reg isolation eventually.

So the new board is working great and is stable ONCE IT STARTS !!!

But sometimes I need to make 3 or 4 resets to make the DAC lock onto the

DSP TDM output. At least I think thats the issue.

I have set the DAC clock to devide/2 , its running a 24.576mhz clock , but

I still need to /2 on in the DSP sigma studio settings to make the outputs work.

I made one obvious mistake on this latest board that was no issue since all the stm32f7 pins are broken out anyway. the spi sclk pin was still hooked up to spi2 where i switch everything to spi1. It could have still worked anyway perhaps if I'd just fired up spi2 sck gpio but I just plugged in a jumper wire into PA5 instead :)

the SPI port is using DMA so you need to use the DMA enabled pins for corresponding Alternate Function mapping.

My next error was the lack of TP's (test points) on the main TDM IO lines between either the ARM or the ADC DAC module boards. I can easily sneak in wires into the module board connectors but it will be harder to find TP's between the DSP and the ARM SAI ports. I deliberately didn't break out these lines to connectors since they will be relatively high speed. TDM8. I'll probebly find some via's if I really need to test these lines, but they are very short traces so they should just work.

There is no micro NOISE and nearly no bluetooth noise detectable even though i'm running the analogue off the digi power supply for now. all good ! This will go away 100% with a bit of shield and separate Power from analogue.

My next analouge board will have the dual rail power board slotted in like the preamps. I will also separate Phantom power , digi power and dualrail power as I seam to becoming a fan of modular plugin board design ! 

I've changed all the GPIO pins for uSD cards SAI ports etc in the firmware and this begins to work. I want to dual record to the uSD cards for redundancy in recording.

Now I need work on the recorder app file manager and bluetooth app for the recorder player. I have the wav file names of recorded files coming back to the BT app but its very clunky !

and find out whats going on with the DAC /2 not working and check through the ADAU1467 startup procedure to make sure I got that correct.