Can't detect i2c devices on Teensy 4.0

Projects Networking, Protocols, and Devices
1

Hi,

I want to connect to a giro/mag MEMS device form Teensy 4.0 but it does not seem to work.

I have two examples of chinese alleged GY6500/9250 9 axis mems giro boards.

My Teensy code does not seem to find them so I ran the standard i2c_scanner sketch from a Uno and it was fine. One device replies to 0x68 the other on 0x69. Both work when fed from either 5V or 3.3V rails.

No I editted the scanner to use the Teensy pinout, first on primary i2c (18,19) then on secondary (17,16). Both sketches reported not finding anything on i2c.

I get that old feeling I'm just being dumb and over looking the obvious.
Can anyone help?

TIA


#include <Wire.h>

void setup() {
// teensy 4.0 pinout
//  Wire.setSDA(17);  //18: sda0, 17: sda1
//  Wire.setSCL(16);  //19: scl0, 16: scl1
  Wire.setSDA(18);  //18: sda0, 17: sda1
  Wire.setSCL(19);  //19: scl0, 16: scl1
  Wire.begin(); // 
  Serial.begin(9600);
  while (!Serial); // Leonardo: wait for serial monitor
  Serial.println("\nI2C Scanner (Teensy 4.0)");
}
2

Well looking at your schematic that you did not post I do not see any pull up resistors connected to SCA and SDL. Of course I could be wrong as what I see is very fuzzy.

3

I did post the sketch in as much as I said it was the standard example scanner sketch. I posted the minimal changes I made , so the info was there.

Also Teensy has built-in pullups, just you lack knowledge of h/w this is running on.

Thanks for taking the time to reply.

4

You are correct I have no experience with this processor but I found this in the data sheet before I answered and I do not see the pinMode in you code.
All digital pins have optional pullup, pulldown, or keeper resistors. These are used to keep the pin at logic HIGH or logic LOW or the same logic level when it is not being actively driven by external circuity. Normally these resistors are used with pushbuttons & switches. The pinMode function with INPUT_PULLUP or INPUT_PULLDOWN must be used to configure these pins to input mode with the built-in resistor.

5

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