Forum Rule: Always post complete source code & details to reproduce any issue!
Results 1 to 7 of 7

Thread: Teensy 4.0 not recognised as comport ?

  1. #1
    Senior Member
    Join Date
    Apr 2019
    Posts
    141

    Teensy 4.0 not recognised as comport ?

    I have got my hands on a T4

    trying to program it and it will not recognise as a device

    Arduino V 1.8.9
    TeensyDuino V1.47
    Windows 7

    i have tried pressing the reset button on T4 and can not get it to work

    T3.2 and T3.6 all work fine

    any suggestions ?

    (I often find a new T3.x takes a while to get recognised when it is time to first program them)

  2. #2
    Senior Member
    Join Date
    Apr 2019
    Posts
    141
    Device was running off a usb extension cable - plugging directly into the usb port has worked

    is the T4 drawing more current than the usb cable can supply ?

  3. #3
    I ran a Teensy 4 the other day with two 16' USB 2.0 active extension cables in series, along with a vacuum feedthru and a 5' micro-USB cable. No problem whatsoever. That said, using any device with multiple active USB extenders can be tricky since they act like a bunch of hubs in series. The total distance and number of hubs is limited at some point.

    The T4 does draw more current than earlier models, but it's around 100mA if I recall correctly. Should not be a problem for any decent cable, even one that doesn't officially meet USB specs. How long was your extension cable? Was it an active cable or just a short passive cable?

  4. #4
    Senior Member PaulStoffregen's Avatar
    Join Date
    Nov 2012
    Posts
    20,580
    The power delivery is pretty easy to check with a voltmeter. Just measure VIN and 3.3V. VIN is the voltage arriving over USB, and the 3.3V pin is the power the regulator is able to make given the USB power. The regulator on Teensy 4.0 has a very low dropout, and the reverse polarity protection is a mosfet (drops very little voltage). So it can probably work with as little as 3.6 or maybe even down to about 3.4 volts.

    Of course, what matters is the 3.3V power. It needs to be 3.0V or higher for Teensy 4.0 to run.

    The other possibility that's almost impossible to check, is the USB signal quality. Teensy 3.x has only 12 Mbit/sec USB, so it can work even with a pretty low quality cable. Teensy 4.0 uses 480 Mbit/sec USB. Low quality extension cables can cause signal reflections or other problems at 480 Mbit/sec speed.

  5. #5
    Senior Member
    Join Date
    Apr 2019
    Posts
    141
    Quote Originally Posted by PaulStoffregen View Post
    The power delivery is pretty easy to check with a voltmeter. Just measure VIN and 3.3V. VIN is the voltage arriving over USB, and the 3.3V pin is the power the regulator is able to make given the USB power. The regulator on Teensy 4.0 has a very low dropout, and the reverse polarity protection is a mosfet (drops very little voltage). So it can probably work with as little as 3.6 or maybe even down to about 3.4 volts.

    Of course, what matters is the 3.3V power. It needs to be 3.0V or higher for Teensy 4.0 to run.

    The other possibility that's almost impossible to check, is the USB signal quality. Teensy 3.x has only 12 Mbit/sec USB, so it can work even with a pretty low quality cable. Teensy 4.0 uses 480 Mbit/sec USB. Low quality extension cables can cause signal reflections or other problems at 480 Mbit/sec speed.
    Thanks for the advice

    the usb extension cable is approx 1m long and is passive - i will try another one tomorrow and report back with the voltages

  6. #6
    Senior Member
    Join Date
    Apr 2019
    Posts
    141
    Quote Originally Posted by Gadget999 View Post
    Thanks for the advice

    the usb extension cable is approx 1m long and is passive - i will try another one tomorrow and report back with the voltages
    there was a voltage drop on the extension lead

    4.17 V on extension
    4.79 v with no extension

    there was 3.3 v with and without the extension lead on the 3V pin

  7. #7
    Senior Member
    Join Date
    Oct 2012
    Location
    Portland OR
    Posts
    676
    Even though in theory the Teensy can still work with it, 4.17 V is not at all within the USB spec, so I would say that is a poor quality cable. 4.79 V with no cable is also a bit lower than I expect direct from any normal USB port, they are usually above 4.9 V, unless it is something like a Raspberry Pi which is itself powered from another USB port.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •