A logic analyzer is a useful tool when working with micro-controllers, but when compared to the price of Arduino compatible boards, they are expensive. While the ability to decode different protocols is a nice convenience, the key functionality of a logic analyzer is the ability to record a signal over a period of time. For low-speed signals in the tens of kbps, a PC audio codec can perform this function.
The audio codecs in most modern PCs are capable of at least 96kbps stereo sampling at 16 bits per sample, with 192kbps/24-bit “HD audio” being relatively common. This is enough to analyze a 38.4kbps UART signal in modest detail (5 samples per bit). With some hardware to connect to the audio input and software to record and view the signal data it is possible to have the functionality of a basic storage oscilloscope and logic analyzer.
Via the comments.