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  1. Replies
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    Well maybe not, but the only step that needs a...

    Well maybe not, but the only step that needs a lot of coefficients is the first oversampling, as the anti-aliasing requirement is
    demanding - thereafter filter requirements are modest. Polyphase...
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    I don't know, I never mentioned transformations....

    I don't know, I never mentioned transformations.

    Transitions is what I was talking about. Logic signals transition between HIGH and LOW and back again. These
    are also known informally as edges...
  3. I've had a play with the class and realized it...

    I've had a play with the class and realized it would make sense for its max buffer to be a settable
    parameter, so that it can play nicely with other classes when being used like this.

    If you...
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    By common representation I meant something like...

    By common representation I meant something like 192kSPS/32bit, ie over-sampled and good bit depth. Computer audio
    sub-systems are pretty complex these days and aren't short of hardware DSP grunt.
  5. I think the whole class needs a good looking at -...

    I think the whole class needs a good looking at - there are two methods not implemented and the semantics seem
    hazy - I presume it should be blocking when the queue is full, and I would like the max...
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    Ive not looked the the USB audio code, its not a...

    Ive not looked the the USB audio code, its not a secret, but its probably quite complex low level DMA stuff.

    I suspect the computer internally is converting to a common representation (perhaps at...
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    Draw a square wave and count the transitions per...

    Draw a square wave and count the transitions per complete cycle. You'll see there are two transitions for each complete
    cycle. Hz is just cycles per second. So 8MHz has 16000000 transistions per...
  8. Judging from my digital camera over the years,...

    Judging from my digital camera over the years, yes data integrity is an issue - sometimes you get bad sectors appearing and
    damaging a file. I don't know if my camera verifies writes though. This...
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    The processor is clocked at 16MHz so can only...

    The processor is clocked at 16MHz so can only sense one transition every 62.5ns, 8MHz has one transition every 62.5ns.

    Use a faster processor. A Teensy springs to mind given which forum this is...
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    The spectrum suggests the host computer's audio...

    The spectrum suggests the host computer's audio system did some rate-conversion or similar that added a bit of extra quantization noise. That FIR
    filter is the null filter. If you save the result...
  11. You overflowed the queue. I think what you need...

    You overflowed the queue. I think what you need to do is ensure AudioMemory is 32 or less, so that getBuffer() will block before
    the queue can overflow, that will give you flow control. I note the...
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    voltage_ratio = 10^(dB/20) dB = 20 *...

    voltage_ratio = 10^(dB/20)
    dB = 20 * log10(voltage_ratio)

    power_ratio = 10^(dB/10)
    dB = 10 * log10(power_ratio)

    power_ratio = voltage_ratio^2, therefore log(power_ratio) = 2 *...
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    This is a job for a state machine. Any...

    This is a job for a state machine. Any multistage interaction with input or output would usually require
    a state machine to track state without locking out other features.
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    You need a style-checking tool like lint for...

    You need a style-checking tool like lint for catching this sort of mistake - there's nothing wrong with the C code as it stands,
    you are allowed to use empty statements and redundant block...
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    I think the anticipated use case is that you call...

    I think the anticipated use case is that you call inputSelect() and then either micGain() or lnputLevel() in setup().

    If you were to dynamically switch between mic and line inputs you'd have to...
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    Erm, that's how the chip is wired - both paths...

    Erm, that's how the chip is wired - both paths use the same switched attenuator. You cannot have both mic and line-in at once
    since there's only one ADC, the attenuator is for the ADC. Mic input...
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    micGain() and lineInLevel() both control it via...

    micGain() and lineInLevel() both control it via the CHIP_ANA_ADC_CTRL register. The micGain() method also sets the coarse mic gain.

    Source in...
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    Anything that waits for (lower priority)...

    Anything that waits for (lower priority) interrupts can be an issue, but more generally avoid anything
    that takes a lot of time or may block (ie does busy-waiting for anything that's not guaranteed...
  19. I presume the serial pin has pullups enabled as...

    I presume the serial pin has pullups enabled as high is the idle state for TTL serial lines. Try turning off the pull up
    for hibernation. The powered down sensor will pull the pin low while its...
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    integer variables in C are modular, so you need...

    integer variables in C are modular, so you need to do the subtraction modulo the relevant power of two. For instance with uint32_t:


    millis start millis-start
    0xFFFFFFF0 0xFFFFFFF0 ...
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    Complete aside: your MyDelay isn't safe from...

    Complete aside:
    your MyDelay isn't safe from wraparound, code it like this:


    void MyDelay(unsigned long WaitTime){
    unsigned long StartTime = millis();
    while (millis() - StartTime <...
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    Indeed, and if you use this you'd implement the...

    Indeed, and if you use this you'd implement the various filter sections using the AudioFilterBiquad class,
    but first you have to generate the filter coefficients - the original code just uses...
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    IPA is not the alcohol it is designed for, it is...

    IPA is not the alcohol it is designed for, it is for ethanol, not isopropanol - the clue really is in the name!!

    Reading a bit more it seems these sensors actually measure permittivity so its...
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    I was thinking save the output to the SDcard...

    I was thinking save the output to the SDcard too... If that works
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    Apparently there are counterfeits of this sensor...

    Apparently there are counterfeits of this sensor around. Do you have an indepedent means to check the output frequency
    such as a 'scope (some multimeters can do frequency too)?

    I believe its 5V...
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    The typical current draw of the screen is stated...

    The typical current draw of the screen is stated as 9mA. So the 2k2 resistor can't really be powering the display, its probably
    being phantom-powered via the I2C pins which is not a good idea at...
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    You mentioned Matlab before - surely it can...

    You mentioned Matlab before - surely it can generate whatever you want?
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    No, the latency is a fixed number of blocks, this...

    No, the latency is a fixed number of blocks, this is just like a pipeline.
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    I've had a quick scan of the code, and I think...

    I've had a quick scan of the code, and I think you need to use two blocks per FFT, so that the overlap
    is 50% of the FFT period - the current code seems to have no overlap.

    BTW a Hann window...
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    A wide-range bandpass filter is easiest to...

    A wide-range bandpass filter is easiest to realize as a high-pass filter and a low-pass filter chained together.
    Can you generate Butterworth low-pass and high-pass filters? There are many on-line...
  31. Sounds travels much faster in solids than air, so...

    Sounds travels much faster in solids than air, so you may have multiple paths for acoustic energy to travel to your sensors unless
    you go for the shortest path inside the solid target itself? In...
  32. That's what I mean - in software you can...

    That's what I mean - in software you can crossfade instantly as well as gradually.
  33. Thread: Measure mV

    by MarkT
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    You need to shift the signal to mid-way between...

    You need to shift the signal to mid-way between the voltage rails. The negative voltages cannot be measured by the ADC,
    and if more than 0.3V or so could damage the chip permanently.

    Normally a...
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    I'd advise always disabling file-hiding in any OS...

    I'd advise always disabling file-hiding in any OS you use, otherwise it will bite you one day.
  35. IC2 is used as a 4-bit address comparator I think...

    IC2 is used as a 4-bit address comparator I think - and is set by the (jumpers?) you've labelled CON. 2
    Until that matches the 245 won't drive anything - is that what writeBoardAddress(3) is...
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    Well as the MOSFET is logic level I'd expect it...

    Well as the MOSFET is logic level I'd expect it to work at any of those voltages no problem.
    I'd suggest careful checking of your circuit, especially the OUTL connection.

    Note the 100nF cap on...
  37. Like all CMOS chips a pair of Schottky diodes to...

    Like all CMOS chips a pair of Schottky diodes to the rails and a series resistor will do the job of protecting inputs.
    To my knowledge exceeding the rails in the inputs by more than a diode drop...
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    You haven't indicated any Vcc in the diagram so...

    You haven't indicated any Vcc in the diagram so its not at all clear what you mean.
  39. You seem to be turning wav file volume on at the...

    You seem to be turning wav file volume on at the same time as microphone volome on, rather than cross-fading -
    I thought you wanted to cross-fade between them?
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    That chip is limited to 10MHz SPI, you need to...

    That chip is limited to 10MHz SPI, you need to ensure the Teensy version sets the SPI clock speed to <= 10MHz.
    The Uno is physically imcapable of clocking faster than 8MHz so it won't see this...
  41. Which module? Is it I2S master or slave?

    Which module? Is it I2S master or slave?
  42. But only in the abbreviated form... Hz stands...

    But only in the abbreviated form... Hz stands for hertz, N for newton, A for ampere. This distinquishes the unit from
    the person (as in "the newton (N) is named after Newton").

    There is one...
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    Grounding the input means connecting it to ground...

    Grounding the input means connecting it to ground (0V normally). Gnd is short for ground
  44. Add an AudioInputI2S and connect it to channels 2...

    Add an AudioInputI2S and connect it to channels 2 on both mixer1 and mixer2.

    Initialize the sgtl5000 to use microphone input and configure the mic gain as necessary. By turning the channel 2...
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    The outputs are not designed to be continuously...

    The outputs are not designed to be continuously shorted even in current limited modes, so always use a resistor with an LED.
    The configuration of output currents is about reducing EMI, not driving...
  46. Forum rule is there for a reason... Post your...

    Forum rule is there for a reason... Post your current code and explain what's not working?
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    Well I think its various lines of code, the setup...

    Well I think its various lines of code, the setup for I2S hardware could be copied from the I2S classes and the BCLK changed to
    16 per sample from the 32 per sample used by the audio library. What...
  48. Uses half as much memory and nearly twice as fast...

    Uses half as much memory and nearly twice as fast I suspect. An N-point FFT with real inputs can be done using an N/2-point complex FFT
    using some clever pre- and post-processing.

    An N-point...
  49. It has various logic to set the mode variable,...

    It has various logic to set the mode variable, and then updates various mixer gains dependent on the mode.
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    An audio device with nothing plugged in is going...

    An audio device with nothing plugged in is going to see the thermal noise from its internal load resistance, which can be considerable if this is
    the standard value (50k). With a low-impedance...
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