The Scanalog 2 is a great inexpensive tool for hobbyists looking to debug digital issues, especially if they can't afford an oscilloscope.  Debug SPI, I2C, Serial UART, 1-Wire, Maple Bus (more to come with software updates). You can even inspect that PWM or RC servo signal to make sure your arduino is outputting what you think it should.

Features:

  • 20Msps on 4 channels
  • 1.8V - 5V level detection
  • 256k samples of storage on each line
  • Playback on all 4 lines, or just 2 while reading from other 2

Wishlist:

  • Better Triggering
  • More flexible output--static pwm to control RC servos, for instance, or just for a clock generator.