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Eagle CAD Drawing v1.5

Eagle CAD PCB Layout v1.5

Results of Running SDInfo.ino

Eagle CAD: v1.5 Bill of Materials

Description:

This voltage level shifter allows you to use modern 3.3v peripherals with older 5v microcontrollers. Actually, the voltage choices are up to you and are only limited by the TI TXS0104 (I2C) and TXB0104 (SPI) chips.

Details:

The top half of the PCB contains the TXS0104 (4 pins) that is used for I2C and its open collectors.

The bottom half of the PCB contains the TXB0104 (4 pins) that is used for SPI.

Plug the level-shifter board into the center of your breadboard (BB).

Wire the 3v3 pin to one BB rail, the 5v pin to another rail and the GND pin to a common ground.

Example Usage:

I2C example: A-HI on the HIGH side connects to SDA from the 5v Uno or Nano, and A-LO on the LOW side connects to SDA on the 3v3 peripheral like an SSD1306 1.3" OLED display

SPI example: a microSD device containing pins SS, MOSI, MISO and SCK. This is a general voltage level shifter and can be used with most digital signals,

Note:

If you don't want to use the TXS0104 (I2C) chip but would prefer to have all 8 input/output pairs for SPI, etc. (not I2C), install two TXB0104 chips instead.

References:

Phillips app note AN97055: bi-directional level shifter for I2C-bus and other systems.

Texas Instruments also has a guide on level shifters.

Pix:

In the left panel you can see pix of the PCB that was sent out for manufacture.

The PCBs returned, one was populated, defluxed and tested with I2C-Scanner.ino and SPI_SD_ListFiles.ino. The results of the I2C Scanner program show the I2C addresses of the BME280 sensor.

Below  are 2 enlargeable screenshots from my Rigol oscilloscope. The signals from the I2C device look pretty good without much signal ringing or overshoot. No pullup resistors were added to the BME280 or OLED devices.