A mini Logic Analyzer wich has 4 inputs, it’s portable (55×65 mm), battery powered and at the moment can capture data upto 100kHz. Vassilis Serasidis writes:
This mini Logic analyzer is a tool for you to watch on LCD the logic transitions 0 or 1 of a digital data signal. A digital data signal can be found on the output pin of TSOP-1730 Infrared Receiver, on the Transmit and reveive pins of MAX-232 chip (RS-232), on Clock and Data pins of I2C data bus and many more electronic components. This circuit is so far limited upto 100 kHz digital signals but this will be changed with a future firmware update.
4-input mini Logic Analyzer - [Link]