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Thread: Teensy 3.6 noise

  1. #26
    Senior Member PaulStoffregen's Avatar
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    Yup, looks like that chip should work fine, as long as you configure it to run in slave mode.

    But the datasheet says the pin pitch is 0.5 mm. That's going to be very difficult to solder. Hand soldering 0.5 mm pitch almost always results in solder bridges between the pins.

    Sadly, it seems parts like WM8783 in relatively easy to solder SOIC-8 packages have gone obsolete. WM8783 probably would have been the perfect chip for you. Looks like CS5381 is one of the last of this dying breed, but it's a relatively large 24 pin part.

    Also a possibility might be PCM1801U, which is still in stock but not recommended for new designs. It'll almost certainly go obsolete in the next couple years. It's also 5V output, but appears to accept TTL level inputs (so 3.3V signals in should work). If you use it with Teensy 3.2 or 3.5 which are 5V tolerant, or put a 5V to 3.3V buffer between its output signal and Teensy's data input, it probably can work. It comes in a SOIC-14 package with fairly easy to solder 1.27 mm pin pitch.
    Last edited by PaulStoffregen; 10-30-2019 at 10:14 PM.

  2. #27
    Senior Member oddson's Avatar
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    If it's only a problem when the output from the guitar is "quiet" and the noise source is from the ADC then one could use an envelop follower from the input level and gate the signal when quiet.

    If you have high gain effects in your planned DSP the will be plenty of noise you're not hearing on a clean channel that will suddenly sound terrible if not gated - even if your ADC is better than the built in.

    Also, has someone suggested the Teensy Audio Board? It's bigger than it needs to be but it's small enough to stuff in a pedal enclosure with a Teensy.
    Last edited by oddson; 10-31-2019 at 12:02 AM. Reason: spelling

  3. #28
    Quote Originally Posted by PaulStoffregen View Post
    Yup, looks like that chip should work fine, as long as you configure it to run in slave mode.

    But the datasheet says the pin pitch is 0.5 mm. That's going to be very difficult to solder. Hand soldering 0.5 mm pitch almost always results in solder bridges between the pins.

    Sadly, it seems parts like WM8783 in relatively easy to solder SOIC-8 packages have gone obsolete. WM8783 probably would have been the perfect chip for you. Looks like CS5381 is one of the last of this dying breed, but it's a relatively large 24 pin part.

    Also a possibility might be PCM1801U, which is still in stock but not recommended for new designs. It'll almost certainly go obsolete in the next couple years. It's also 5V output, but appears to accept TTL level inputs (so 3.3V signals in should work). If you use it with Teensy 3.2 or 3.5 which are 5V tolerant, or put a 5V to 3.3V buffer between its output signal and Teensy's data input, it probably can work. It comes in a SOIC-14 package with fairly easy to solder 1.27 mm pin pitch.
    thanks Paul, I'll have a look at these...dont care if they go obsolete in a couple of years

    I already soldered msop (0.3mm leads) packages, but it is hard to do without damaging the chip

    I dont even know what is the max temperature to use , guess it depends on the chip

    AFAIK, for 3.3->5v, it works without the need of conversion, and 5V->3.3V, a simple 1k/2k divider does the trick :-)
    Last edited by bob1984; 10-30-2019 at 11:20 PM.

  4. #29
    I use 9V batteries, I was hoping such power supply would be quite enough

    the cavity (I already digged and shielded) is not large enough to accomodate the teensy audio board (although I could maybe trim it to a certain extend)

    Click image for larger version. 

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    Last edited by bob1984; 10-30-2019 at 11:07 PM.

  5. #30
    Quote Originally Posted by Theremingenieur View Post
    A quick look into the source code of the I2S objects of the audio lib will tell you that one frame contains two 32bit words (one per channel). The audio lib does use 16bit audio which means that the least significant bits will be ignored. Thus, your 24bit ADC will use 24 of the 32 available bits, leaving the remaining 8 least significant bits equal zero. The audio lib will then use the 16 most significant of these 24 bits and truncate the 8 LSBs. So, everything should work for you, if you set the CS5343 up in slave mode (10k resistor from SDOUT to GND) and configure everything for single speed mode with 256x MCLK/LRCK and 64x SCLK/LRCK.

    And, for heaven's sake, please respect to avoid another disappointing situation:

    "As with any high-resolution converter, designing with the CS5343/4 requires careful attention to power sup- ply and grounding arrangements if its potential performance is to be realized. Figure 3 shows the recommended power arrangements, with VA connected to a clean supply. Decoupling capacitors should be as near to the ADC as possible, with the low value ceramic capacitor being the nearest. All signals, especially clocks, should be kept away from the FILT+ and VQ pins in order to avoid unwanted coupling into the modulators. The FILT+ and VQ decoupling capacitors, particularly the 0.1 μF, must be positioned to minimize the electrical path from FILT+ to GND. The CDB5343 evaluation board demonstrates the optimum layout and power supply arrangements. To minimize digital noise, connect the ADC digital outputs only to CMOS inputs."
    I'll check the datasheet indeed, thanks mate
    Last edited by bob1984; 10-30-2019 at 11:07 PM.

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