To fix this, I manually installed matplotlib (apparently only the older version works - 0.99.1.1). Boom. That did it. Now I can load both visual and pylab modules at the same time.

The Arduino library is available on Github, and you can order a SI5351 breakout board from OSHPark. Posted in Arduino Hacks, Radio Hacks Tagged arduino, clock, PLL, radio, SI5351.