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  1. I think I did measure the performance of the...

    I think I did measure the performance of the various FFT types a while back on the T4, though I guess it matters more
    on slower chips - I only have T4.0 and T3.2 at the moment to play with.

    The...
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    Well I guess you just have to assume they are the...

    Well I guess you just have to assume they are the same, or close enough, and apply the equations anyway - the
    test circuit is ratiometric so the absolute resistance isn't important.
  3. You can implement a waterfall without scrolling...

    You can implement a waterfall without scrolling...
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    Because chips like this are synthesized from...

    Because chips like this are synthesized from hardware description libraries shared between many other chips, the
    silicon foundaries don't start afresh for each design, they have libraries of...
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    Resistive touchscreens are an overlay, typically...

    Resistive touchscreens are an overlay, typically having a 4 wire flat-flex cable going the PCB in a different place to the
    main CoG flatflex.
  6. Hard to guess if you don't follow the forum rule...

    Hard to guess if you don't follow the forum rule and post your code... What kind of noise? Do you have any
    data/graph/spectra to show?
  7. A and #A form a pair, B and #B form a pair -...

    A and #A form a pair, B and #B form a pair - those can be routed as twisted pairs, but twisting A with B will risk
    crosstalk between the quadrature channels.

    Each RS422 pair needs termination...
  8. Comparisons of the generic fft v. the existing...

    Comparisons of the generic fft v. the existing FFT1024, for several windows, with
    input being 5 test tones at -1dB, -20dB, -40dB, -60dB and -80dB compared to full scale sine.

    23877

    Notable is...
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    Unplug it, stick a multimeter on X-/X+, and...

    Unplug it, stick a multimeter on X-/X+, and Y-/Y+...
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    Had another look at the XPT2046 library code and...

    Had another look at the XPT2046 library code and it doesn't calculate Z values as per the datasheet, so its
    sentitivity is inherently poor in one corner. The raw readings of x, y, z1, z2 have to be...
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    The T4 is a dual issue processor so you can get...

    The T4 is a dual issue processor so you can get upto 1200 million instruction cycles per second with luck,
    but yes the clock period is 1.67ns = 1/600000000s, so 9 clocks is 15ns
  12. Timer1.initialize(10000000); // 1 Hertz ...

    Timer1.initialize(10000000); // 1 Hertz

    That's 10 million, not 1 million.
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    96kSPS is the highest supported data rate...

    96kSPS is the highest supported data rate according to the datasheet, which uses MCLK = 24.576MHz (x256)
  14. You are probably not allowing dead-time between...

    You are probably not allowing dead-time between switching off one set of LEDs and switching on
    the next set - the LED junction capacitance and stored charges may be holding enough charge
    for...
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    Well I'd call them completely different. I2S...

    Well I'd call them completely different. I2S requires a stable set of clocks, all phase-locked to each other and low jitter,
    running continuously and communicates a pair of digital audio channels...
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    No current limiting?

    No current limiting?
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    The library has no hysteresis for Z_THRESHOLD so...

    The library has no hysteresis for Z_THRESHOLD so will inherently generate noisy z-values. This
    probably is an oversight. The Z-threshold(s) probably ought to be tweakable in the API too.

    Your...
  18. With white LEDs the high forward voltage allows...

    With white LEDs the high forward voltage allows the resistors to be smaller, but 75 ohms sounds risky - for instance
    no pin on the T4 can handle more than 4mA at max drive level, and 4mA through 75...
  19. Let me say it again: Nothing to do with pull-up...

    Let me say it again: Nothing to do with pull-up resistors. Nothing.

    And do you have current-limiting resistors? You need them to protect the output pins from overload.


    [ Here's one way to...
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    PWM hardware can't run parallel Bresenhams for...

    PWM hardware can't run parallel Bresenhams for concerted stepper motor movement, so it has to be bit banged I believe.
    (For instance for circular motion you can't set a fixed frequency...)

    T4 is...
  21. Nothing to do with pullups. With N pins you...

    Nothing to do with pullups.

    With N pins you can charlieplex N(N-1) LEDs and light at most N-1 up at once, and only then if they all share
    the same pin as the same sense (anode or cathode). ...
  22. Not sure they are documented, I read the audio...

    Not sure they are documented, I read the audio lib source in depth a while back. There may be some
    issues if you randomly play with connections, I recall somewhere there's a thread or two about...
  23. The MAX98306 is a CMOS chip, so will be fragile...

    The MAX98306 is a CMOS chip, so will be fragile w.r.t. static.
    The Adafruit breakout for it has no schottky protection diodes on the chip inputs so its vulnerable to this (same
    issue with the...
  24. You need a more useful meter I'm afraid, with...

    You need a more useful meter I'm afraid, with millivolts AC (!)

    Where's the call to lineOutLevel(13)?:


    // Comment these out if not using the audio adaptor board.
    // This may wait forever...
  25. AudioConnection has these public methods that...

    AudioConnection has these public methods that deal with attaching and detaching from the signal graph:


    void disconnect(void);
    void connect(void);

    The constructor calls connect(), the...
  26. Good question - I've not heard of such, but these...

    Good question - I've not heard of such, but these chips have big datasheets!

    Any differential receiver ought to be high impedance, and at 1Mbps / 100ohms pin capacitance is unlikely to be an...
  27. I have a fairly stable implementation now for an...

    I have a fairly stable implementation now for an improved FFT along these lines, although it
    turns out only the T4.x have a decent implementation of arm_rfft_q31 with a wide range of
    points from...
  28. You've not shown your code. Have you called...

    You've not shown your code.

    Have you called "sgtl5000_1.lineOutLevel();" or similar to configure the line outs? Have you checked
    there's a signal on the line outs using AC volts setting of...
  29. Thread: Pot Jumpin'

    by MarkT
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    The main issue with high impedance inputs is...

    The main issue with high impedance inputs is noise coupling to it from nearby signals - logic signals switch so fast that
    even tiny amounts of stray capacitance will induce significant currents.
    ...
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    That's a dangerous circuit - press both buttons...

    That's a dangerous circuit - press both buttons and the supply is shorted out, possibly welding the switches shut too.

    Also when neither button is pressed the pin is left floating, so that its...
  31. Thread: Pot Jumpin'

    by MarkT
    Replies
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    Could this just be a scratchy pot? This can be...

    Could this just be a scratchy pot? This can be cured with a small capacitor from the wiper to ground, 100nF or similar.

    100k is a bit high for a pot, more likely to pick up noise than ones of 5k...
  32. https://www.pjrc.com/teensy/gui/?info=AudioInputI2...

    https://www.pjrc.com/teensy/gui/?info=AudioInputI2S
    look for "compatible microphones" and some of the examples mentioned are probably useful.
  33. Depending on the drive level set, pins are rated...

    Depending on the drive level set, pins are rated from 1mA upto 4mA at full drive, sourcing or sinking.

    BTW csv: you did call "pinMode (..., OUTPUT);" didn't you?
  34. My point was that the ADS1115 is inherently...

    My point was that the ADS1115 is inherently integrating over its long sample period, so will have relatively little issue
    with wideband noise at the input.

    If you want a fast >=16 bit ADC, the...
  35. The recommendation from TI seems to be direct...

    The recommendation from TI seems to be direct grounding at host end, ferrite beads to groundplane at client end. https://www.ti.com/sc/docs/apps/msp/intrface/usb/emitest.pdf
  36. The LTC1867 only claims 89dB SNR, which is about...

    The LTC1867 only claims 89dB SNR, which is about 14.5 bits equivalent.
    The ADS1115 claims full 16 bit noise-free at lower rates and not far off 16 bits at the full 860 SPS.

    Couple this with the...
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    Sorry for the delay in replying. Recently been...

    Sorry for the delay in replying. Recently been tidying up some old branches and spotted this.

    Its a bug in the folder, whenever the folder saw a sample value ending in 0x8000 it was glitching.
    ...
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    Ah, those are my PDM changes, I noticed them...

    Ah, those are my PDM changes, I noticed them eventually - I'll have a look at fixing this.

    [ pull request https://github.com/PaulStoffregen/Audio/pull/390 ]
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    As aside about switches - its been briefly...

    As aside about switches - its been briefly mentioned above I think, but hard switching of audio is going to
    produce potentially loud and annoying clicks, since truncating a waveform is equivalent to...
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    8MB? SDcard? No, that's going to take a while I...

    8MB? SDcard? No, that's going to take a while I think.

    You don't want to let that amount of data go without backup anyway, so why not flush it to backing store
    regularly so there's never that...
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    My other thought was a busy-waiting loop would be...

    My other thought was a busy-waiting loop would be entirely in cache and avoid hitting RAM for instruction fetch or any load/stores.
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    Switch-mode power supplies don't need such large...

    Switch-mode power supplies don't need such large capacitors as they can pull power from the waveform
    when its well below peak voltage, and thus don't have to store as much energy as a...
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    The drop in current suggests the processor is...

    The drop in current suggests the processor is halting and waiting for interrupt. Bulk SPI
    operations are probably being DMA'd.
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    Little tip about PCB prototypes - ensure every...

    Little tip about PCB prototypes - ensure every important signal has at least one via not covered by a component -
    these make convenient points to stick a thin wire in for either 'scope/LA probing...
  45. Fig 37.2 in the processor manual shows that the...

    Fig 37.2 in the processor manual shows that the way I2S data inputs and outputs are multiplexed in SAI1
    is:


    function T4 name T4 pin no
    RX0 IN1 8
    TX3 / RX1 OUT1D 6...
  46. Surely you can have a setup with one ADC or DAC...

    Surely you can have a setup with one ADC or DAC as master, and everything else as slave, including Teensy? The clocks are
    routed from the master to everything, which should mean the Teensy can run...
  47. Its probably doing the bass boost by attenuating...

    Its probably doing the bass boost by attenuating the other frequencies - simply up the overall gain with the volume()
    and/or lineOutLevel() methods?
  48. The way I'd do this is populate a lookup table...

    The way I'd do this is populate a lookup table with RGB values indexed by decibel. Then run through the
    FFT bins converting the value to decibels, lookup the pixel colour and write that to the...
  49. Thread: Bat detector

    by MarkT
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    78,907

    Actually LP2950Z took me to a Micrel datasheet...

    Actually LP2950Z took me to a Micrel datasheet which is a 5V only part.

    There is indeed an LP2950-33 from TI. The '50' in the part number strongly suggests 5V too.
  50. Thread: Bat detector

    by MarkT
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    78,907

    The LP2950 is 5V and is the wrong part number on...

    The LP2950 is 5V and is the wrong part number on the schematic as far as I can see - you need a 3.3V output regulator
    in that position or bad things happen. Its not uncommon to see the wrong part...
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