I completed the first Speaker that uses two Amp2 and a DAC+ADC for the I/O. All audio processing is done with the Teensy4.0
Everything fits into the back of the speaker.
Sounds great. Startup time is about 3 seconds. But only because the software is only a prototype. Could be faster. About a second would be good.
Sound pretty cool. Do you share the source code of your software?
At the moment I would not show the code as it is somewhat weird/unordered/mashup of different sources besides some of my own ideas. But I can give a short description. And whoever may interested in more information can ask here.
The startup code is taken from the Teensy example program that runs as "smoketest" in the teensy.
I stripped many parts, about 80%, of this example as it contains many functionality that I do not need.
I removed almost any code that comes from the Arduino environment. There are only some definitions left that are needed for the startup code.
For the hardware configuration I used the NXP MCUXpresso IDE. That makes it very easy to create the initialization code for the hardware.
As I expected a high CPU load only the low-level drivers are used, no CMSIS.
The audio processing can be done within the interrupt handler. About 3microseconds are needed for all audio calculation.
The audio calculations contain a correction filter for frequency response of the speaker chassis and behind that some cutoff filters to split the signal into three. That code is some simple biquad implementation that works well.
The two low frequency chassis run the same data. So the low frequency part of the signal has some sort of boost by using to amplifiers for the same signal.
The frequency response has been measured the room equalization wizard REW. With the equalizer function of the tool a text file can be generated that contains the filter parameter for the correction. An awk-script than produces a header file with the C code for filter intialization.
To reduce the overall delay between input and output a 96khz sample rate is used. This makes up about a 10microsecond cycle time. The audio processing only needs 3microseconds. So there are a lot of time for some functional safety things. Like checking the program code.
As the Teensy copies the code from flash to RAM it is needed to check the code in RAM regularly.
The ADC is used to make the power line monitoring. This way the mute line gets drawn if the power supply shut off. That monitoring is done in the interrupt handler as well and it works. Silence on power off ;)
I2C bus handling is something new to me and so I build a small statemachine. At the moment I only need to send out the configuration data to the HifiBerry boards. As the DAC+ADC and the Amp2 share all the same I2C address I inserted a I2C multiplexer.
For some of the maintenance functions that are needed later on I use some sort of simple task scheduler. I have several task containers that will be run on 20ms and 500ms schedule. I can add any schedule time as needed. These task containers are run outside of an interrupt handler.
Debugging has been done with simple text output through the serial line and intensive use of my brain. Sometimes scullcracking.
At the moment temperature monitoring, a command interpreter through the serial line and CRC runs on the copied code are missing. Maybe a bluetooth module and an Android App for controlling the software would be great. Parameter memory is needed as well and some boot loader that does the flashing of new software while running.
A 150W-Meanwell SPS is used for the power supply. Even on normal music levels the SPS runs the whole thing for about 3 seconds.
As I expect that I may switch on my whole AV equipment with a powerstrip I added a rush in current limiter. A simple one. But it looks like it works.
On question comes to my mind:
Is it possible to connect to the mute line for the power stage of the Amp60 board? Even a wire would do. But it would be good to know where to connect that wire.
As the power monitoring works for the simple version with the DAC+ADC and Amp60as well and suppresses the power off spike on the output. It does not work for power on as it does for the Amp2.