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Thread: Triage a possible short

  1. #1
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    Triage a possible short

    I have two Teensy 3.2. They both are (intended to be) soldered the same way with connections on the back side GND and VUSB pads, on the back side below the micro-USB plug. The third wire connection is soldered into pin hole 2. They both have the same code on them and I am testing with the exact same USB wire and WS2811 strip. When plugged into my Mac's usb port and not under load they both register 5V across the pads. One of them is able to run the installed program to control and illuminate a WS2811 strip, while the other is not. Interestingly the Teensy that does not light the LEDs properly only registers 0.58V when the the lights are plugged in. Does this mean there is likely a short somewhere in the Teensy? Is there anything I can do?

  2. #2
    Senior Member+ Frank B's Avatar
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    Has the not working Teensy 5V when the LEDs are NOT plugged in?

  3. #3
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    Yes. Let me be more precise by giving you voltage values.
    The circuit is MacBook Pro usb-C port connected to USB-C/USB adaptor connected to USB-A to USB-microB cable plugged into Teensy 3.2 soldered to JST 3 pin connected to WS2811.

    With the good Teensy:
    I disconnect the WS2811but leave the rest of the circuit connected. Voltage across VUSB to Ground is 5.20V, Reconnect the WS2811 LED strip and the voltage is now 4.78V. The LEDs are illuminated.

    Repeating with the problem Teensy and only swapping the Teensy and the soldered on JST wire:
    I disconnect the WS2811but leave the rest of the circuit connected. Voltage across VUSB to Ground is 5.17V, Reconnect the WS2811 LED strip and the voltage is now 0.58V. The LEDs are NOT illuminated.
    Note that after this test the Teensey does not seem particularly hot, nor does the computer complain that the USB device is drawing too much current and has been automatically disconnected, which it has done in cases of an unintentional short.

    Since I am using all the same wires and components, I wonder if it is either the Teensy, the JST wire or my soldering.

  4. #4
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    As an additional test I wired up the Tutorial 2 example on a breadboard using the following code and was able to get it to light all 3 LEDs correctly (holding the red LED wire in contact with the soldered redPin = 2). So therefore pin 2 is able to send turn on and off.

    int redPin = 2;
    int greenPin = 15;
    int bluePin = 22;

    // The setup() method runs once, when the sketch starts

    void setup() {
    // initialize the digitals pin as an outputs
    pinMode(redPin, OUTPUT);
    pinMode(greenPin, OUTPUT);
    pinMode(bluePin, OUTPUT);
    }

    // the loop() method runs over and over again,

    void loop()
    {
    digitalWrite(redPin, HIGH);
    delay(500);
    digitalWrite(greenPin, HIGH);
    delay(500);
    digitalWrite(bluePin, HIGH);
    delay(500);
    digitalWrite(redPin, LOW);
    delay(500);
    digitalWrite(greenPin, LOW);
    delay(500);
    digitalWrite(bluePin, LOW);
    delay(500);
    }

  5. #5
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    Yes, for the problematic Teensy:
    Without the LEDs, voltage across is 5.17V. With the LED strip, the voltage is now 0.58V. The LEDs are NOT illuminated.

  6. #6
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by BurnerBoard View Post
    I wonder if it is either the Teensy, the JST wire or my soldering.
    We could offer a better opinion if we could actually see this stuff... like with photos.

    Or maybe you could be more specific about what a "JST wire" really is? Maybe a link?

    Just a blind guess (literally blind - can't see), maybe it's one those little wires commonly sold for use on solderless breadboards, where the ends of little metal pins? Those wires have almost no copper inside. Some of them measure almost 1 ohm of resistance, if you have a good quality 4-wire resistance measurement on your multimeter. Definitely do not use that sort of wire for the power or ground connection to LEDs!

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