6bit Digital-Analog-Converter

Expending six Pico GPs (or more) may be rather impractical in some projects. 

The I2C bus would need only two connections, so one can go with an additional I2C IC, such as the MCP23016 or MCP23017 I/O expansion.

Having all circuits work smoothly together was for me a hassle though. Issues probably stem from the Pico's internal pull-up resistors which are generally not so well-suited for the I2C bus (values range from 50k to 80k, according to the data sheet). 

Small-value resistors provide improved noise immunity as well as increased speed, so I soldered two external 3.9 kOhm and de-activated the internal ones via SW.