- Support for 4x20 LCD Display and large number display
- Brightness and contrast adjustment with remote
- (OPUS/Wolfson WM8741) DAC volume control: remote and rotary encoder
- (OPUS/Wolfson WM8741) DAC random filter selection 1 to 5 with remote
- (OPUS/Wolfson WM8741) DAC upsampling selection (L, M, H -this is the OSR setting)
- I2C level shifting (5V to 3.3V)
- Optimized power-up sequence

Saturday, April 25, 2009

Implemented 5V to 3.3V I2C level Shifting

Implemented the circuit with the two MOSFETs (page 10 of this application note). The opto isolator has to be ordered from Digikey and that will take a while. I couldn't find MOSfets at the local electronic shop so I cut a piece out of a junk board, removed all the components around the transistors and rewired it (so ignore the white drawing in the board). The MOSfets threshold voltage are nominal 2V which is on the high side of the specified components, but it works. The 5V side measures at 5V and the 3.3V side measures 3.3V.

The 5V i2c connects to the LCD and the 3.3v connects to the DAC. Now I have piece of mind.
The pull-up resistors for the 5V side are back to 5V. Thanks to PJotr who alerted me.

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