Teensy 4.0 I2C comms with Adafruit MCP4725 DAC board

[Frank_and_Beans]

Hi All,

I'm having an issue with the Teensy 4.0 connecting to an Adafruit MCP4725 DAC breakout board.

Warning - I'm dumb.

Facts:
1) Using Arduino IDE 1.8.10 (latest version at time of writing)
2) Using Teensyduino 1.48 (latest version at time of writing)
3) Using MCP4725 DAC breakout board from Adafruit with 3.3V power and connecting SDA to pin 18 and SCL to pin 19 on Teensy 4.0
4) Datasheet from Adafruit shows 10kohm pullup resistors on both SDA and SCL https://learn.adafruit.com/assets/36265
5) Using Adafruit library here: https://github.com/adafruit/Adafruit_MCP4725
6) Using standard sketch from the libarary to generate a triangle wave https://github.com/adafruit/Adafruit_MCP4725/tree/master/examples/trianglewave
7) I verified that the sketch and hardware works fine on a Teensy 3.2


Here is scope data on the SDA and SCL lines with SDA disconnected from the MCP4725


And, here is what happens when I connect the SDA line:


So, what am I missing between the Teensy 4.0 and 3.2? Why would it work with one, but not the other?

 

[Frank_and_Beans]

Well, I have proven myself right. I am dumb.

I forgot that full size proto breadboards don't have continuous power rails. Oops. Wiring problem solved. Teensy 4.0 works fine.

 

[PaulStoffregen]

Glad you got it working, and thanks for the followup. I was just about to wire one up here and test it.