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Thread: Killed my First Teensy 4.0

  1. #1
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    Killed my First Teensy 4.0

    Don't know WHAT I did, I was setting up 5 buttons to run on a single analog pin and a 20x4 display. All was A-Okay. buttons didn't work right.. then... the display shut off. Now there is no 3.3v And its not recognized by the PC any more. Anyone have any luck resurecting one of these from an incident like this?

  2. #2
    Senior Member+ defragster's Avatar
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    Quote Originally Posted by Hotwire View Post
    Don't know WHAT I did, I was setting up 5 buttons to run on a single analog pin and a 20x4 display. All was A-Okay. buttons didn't work right.. then... the display shut off. Now there is no 3.3v And its not recognized by the PC any more. Anyone have any luck resurecting one of these from an incident like this?
    If everything is disconnected and rested some time and then USB powering doesn't show 3.3V that's a bad sign.

    No idea what pins and what was connected - any chance 5V was involved or touched? Is the 20x4 display a 5V device?

  3. #3
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    The display is a 5v i2c device. It was attached to 5v, Gnd, SDA0 and SCL0.

    The switches were attached to GND, 3.3v and Pin 14 (A0).

  4. #4
    Senior Member+ defragster's Avatar
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    Quote Originally Posted by Hotwire View Post
    The display is a 5v i2c device. It was attached to 5v, Gnd, SDA0 and SCL0.

    The switches were attached to GND, 3.3v and Pin 14 (A0).
    5V i2c device possibly/likely pulling those pins up to 5V - at least when doing output if not hosting pullups to 5V - not acceptable to the T_4.0.

  5. #5
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    So its toast.. Iv got a spare... because I KNEW the first one was going to be sacrificial.

    Thank you!

  6. #6
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    Yeah - 5V bad news for a T_4's 1062 ... just like the T_3.6 ... High speed and great features mean the silicon underpinnings are cramped and design limited to 3.3V.

    Glad you have a spare on hand ... if you put 5V on the display without T_4.0 connected a DVM will probably see 5V on the SDA and SCL lines.

  7. #7
    ok, so what is the best way to interface with one of those 128x64 5v OLED displays on a teensy 4? level shifter? voltage divider?

  8. #8
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    There are a lot of ways to accomplish that. If you don't need to read from the display, I would consider using simple TTL logic rather than a specialized level shifter. A $0.50 part works great. If you need 4 pins, use a 74AHCT125 or 74HCT125. If you need up to 8 pins, use a 74AHCT541 or 74HCT541. These are buffer chips - "non-inverting". They will take anything over 2V as a high (or logic 1) and output a 5V signal so work great for interfacing 3.3V logic to 5V chips. Adafruit has a write up on that here.

  9. #9
    Are you sure it wasn't the switches?

    Didn't you say you may have miswired them?

    You wrote, "The switches were attached to GND, 3.3v and Pin 14 (A0)."

    Any chance that when you pressed a button it shorted 3.3 VDC to ground?

    If you no longer have 3.3 VDC on the board, then either something is shorted or the voltage regulator is bad. Is there +5 VDC at the regulator input?

    You may also want to finger test the MPU. Place your finger on the chip and then apply power. If it gets hot to the touch you can pretty well assume the processor is bad. If not, I would start with the power supply circuit, trace from the USB power pin #1, and see where you lose power.

    The voltage regulator (TLV757P) also has a 100 mA maximum current before it automatically shuts down. So, if there is no 3.3 volts, then it may be there is a short on the board. Try measuring the impedance to ground at 3.3 VDC (with power disconnected).

  10. #10
    Good question, I need to research!

  11. #11
    Senior Member PaulStoffregen's Avatar
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    While not good, normal I2C pullup resistors to 5V should not kill Teensy 4.0 or 4.1. The chip has ESD protection diodes. NXP doesn't rate them for handling any level of continuous current, but in reality they can pretty easily handle a couple mA.

    As a quick test, I put two 1K pullups to 5V on this Teensy 4.1.

    Click image for larger version. 

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    I ran the Wire library Scanner example, and also the LED blink example (to test what happens if the pins aren't in I2C mode). My voltmeter says both pins are at 3.9V. I can confirm this Teensy 4.1 is still working.

    I can't say what happened to your Teensy, but hopefully this helps to rule out the I2C pullup resistors.

  12. #12
    Quote Originally Posted by PaulStoffregen View Post
    While not good, normal I2C pullup resistors to 5V should not kill Teensy 4.0 or 4.1. The chip has ESD protection diodes. NXP doesn't rate them for handling any level of continuous current, but in reality they can pretty easily handle a couple mA.

    As a quick test, I put two 1K pullups to 5V on this Teensy 4.1.

    Click image for larger version. 

Name:	1k.jpg 
Views:	5 
Size:	84.6 KB 
ID:	20404

    I ran the Wire library Scanner example, and also the LED blink example (to test what happens if the pins aren't in I2C mode). My voltmeter says both pins are at 3.9V. I can confirm this Teensy 4.1 is still working.

    I can't say what happened to your Teensy, but hopefully this helps to rule out the I2C pullup resistors.
    Thank you!

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