Teensy 3.5 -- program running, 3V3 voltage pins have zero voltage

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zoldak

Member
Hello,

I supply Teensy 3.5 from 5V voltage regulator (78L05) connected to Vin.
Wanted to test ISR routine by connecting 3.3V/GND to INPUT.

I expected LED to light off after touching 3.3pin but i realized that 3.3V voltage is not there(measured zero).

How is that possible? It seems I use original board (compared to photos of counterfeits) and schematic shows 3.3V supplies everything onboard.

I tried to hook 5V/GND to few INPUT pins, but program does not call ISR. I was using external interrupts on Arduino Unu without any problem. This is my second question.

I can provide any other info if needed.

Thank you very much for any attempt to help.


source:

Code:
const byte pin_lcd_rs = 10;
const byte pin_lcd_en = 9;
const byte pin_lcd_d4 = 5;
const byte pin_lcd_d5 = 8;
const byte pin_lcd_d6 = 6;
const byte pin_lcd_d7 = 7;

const byte pin_led = 2;
const byte pin_hall = 25;

void isr_hall()
{
    digitalWrite(pin_led, LOW);
}

void setup()
{   
    pinMode(25, INPUT);
    pinMode(pin_led, OUTPUT);

    digitalWrite(pin_led, HIGH);
    
    pinMode(pin_lcd_rs, OUTPUT);
    pinMode(pin_lcd_en, OUTPUT);
    pinMode(pin_lcd_d4, OUTPUT);
    pinMode(pin_lcd_d5, OUTPUT);
    pinMode(pin_lcd_d6, OUTPUT);
    pinMode(pin_lcd_d7, OUTPUT);  
    attachInterrupt(digitalPinToInterrupt(25), isr_hall, RISING);
    
}


void loop()
{
}
 
Is pin 25 connected to anything? If not it is probably just floating and as such you might not see any changes to get the rising.
You might either connect it with some external pull down resistor.

Or maybe change the pinmode above to something like: pinMode(25, INPUT_PULLDOWN);
 
Is pin 25 connected to anything? If not it is probably just floating and as such you might not see any changes to get the rising.
You might either connect it with some external pull down resistor.

Or maybe change the pinmode above to something like: pinMode(25, INPUT_PULLDOWN);

Hi KurtE!
Tried internal pulldown approach and used previously unused pin (33). Same problem, LED does not turn off, ISR is not called.

I ordered 2 new Teensies 3.5 to verify mine is not broken.

Strange thing is program works (LCD displays text), i can upload blinking program etc. But interrupts are not working and i cannot measure any voltage on 3.3V pins ...

Code:
const byte pin_lcd_rs = 10;
const byte pin_lcd_en = 9;
const byte pin_lcd_d4 = 5;
const byte pin_lcd_d5 = 8;
const byte pin_lcd_d6 = 6;
const byte pin_lcd_d7 = 7;

const byte pin_led = 2;
const byte pin_hall = 33;

void isr_hall()
{
    digitalWrite(pin_led, LOW);
}



void setup()
{   
    pinMode(33, INPUT_PULLDOWN);
    
    pinMode(pin_led, OUTPUT);

    digitalWrite(pin_led, HIGH);
    
    pinMode(pin_lcd_rs, OUTPUT);
    pinMode(pin_lcd_en, OUTPUT);
    pinMode(pin_lcd_d4, OUTPUT);
    pinMode(pin_lcd_d5, OUTPUT);
    pinMode(pin_lcd_d6, OUTPUT);
    pinMode(pin_lcd_d7, OUTPUT);  
    attachInterrupt(digitalPinToInterrupt(33), isr_hall, RISING);
    
}


void loop()
{
}
 
Maybe show picture? like maybe cold solder joint?

Or if for example you are trying to use a breadboard, and have not soldered the pins, will typically not work. Also Teensy has 3.3v on a few different pins, have you tried measuring with volt meter to the different ones?
 
I can exclude cold joint because i tried 4 different pins. I measured Vin, which is 5V, but voltmeter shows nothing on both 3.3V pins (pin below 12 and pin below Analog GND).
Sorry, but photo is impossible due to broken camera. I will draw it in QCAD but it takes some time.

I used similar setup with Arduino Uno and worked well....had to migrate program due to lack of RAM on Arduino Uno (2KB vs 192KB).

I am stuck.
 
On T3.5, I changed pin_led to 13, and your sketch worked if (as Kurt suggested) i used pinMode(25, INPUT_PULLDOWN);. LED goes off when i jumper 3v3 to pin 25.
 
I also suspected installation as culprit. Deleted old installation, installed Arduino 1.8.5 and Teensyduino. Same problem. I am on Linux, but everything compiles fine.
I know there is some interrupt controller inside chip but i don't know why or how it might become damaged.
 
Hello manitou,
that's exactly what i expected. Seems like i somehow fried something in Teensy. Programs not using ISRs seem to work. Does anyone ever noticed same behaviour? I am really convinced that i applied voltage to pins (5V), measured it.

Many thanks to everyone who tries to help.
 
0v on 3.3v pins? eeek! do you have both USB power and your external 5v connected at the same time?
what happens if you get rid of your external power connection and just power with USB?
 
No voltage on pins labeled 3.3V (below pin 12), no voltage on pin 3.3 (250mA max) below Analog GND.

Board looks original as I stated above (compared to "Welcome to Teensy(R) 3.5 card i got when i purchased it) and against pictures of common counterfeits that i saw on https://pjrc.com site.

I tried uploading blinking program and then program displaying message on LCD. It works. But ISR is not triggered and no 3.3V voltage is present on both pins. I measure ~ 5V on Vin. Did several times, same result.
 
do you have a friend with a smart phone that can take a picture of your T3.5 and wiring?

Well...not here...but i found (shame) some unsoldered pins on T3.5 bottom, it's soldered into perfboard, single-pin islands....testing for shortcuts.
Hope everything will work now. Sorry for wasting your time because of my silly mistake :(

I will post message when i upload program...
 
3.3V is there now...interrupts seem to work....Problem is Hall sensor now.
Many thanks to manitou and KurtE for their time and care.
 
BTW - the T_3.5 now has access to full 256KB like the T_3.6 ( except -8 bytes ) of RAM - not the 192KB first thought ( when using TD 1.42 and above )

...
I used similar setup with Arduino Uno and worked well....had to migrate program due to lack of RAM on Arduino Uno (2KB vs 192KB).
...
 
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