USB Logic Analyzer debug tool is a very cheap and useful debugging tool for digital signal analyzing.
If you don’t want to start with an expensive oscilloscope, this will be another good choice. A total of eight digital channels, the voltage range is 0V ~ 5.5V, the voltage threshold is considered to be low below 1.5V, 1.5V above is considered high. 24 m sampling rate, can automatically analyze UART, IIC, SPI, and much other standard protocol.
If you do single-chip development, ARM system development or FPGA development then we strongly recommend you buy this product.  Especially do UART, SPI, IIC communication debugging, 
Specifications and Features:
Logical light indication: a small light indicate CHO electrical level.
Input feature: 5PF,100K Ohm.
USB power supply; USB logic analyzer for monitoring, analyzing and debugging digital circuits
8-Channels USB logic analyzer with a 24Mhz sampling frequency
Can analyze UART, IIC, and SPI, etc automatically
Great for MCU, ARM system and FPGA development
Voltage: 0-5.5V
Threshold Voltage: 1.5V
The sampling rate can be set as below:
24MHz, 16MHz, 12MHz, 8MHz, 4MHz, 2MHz, 1MHz, 500KHz, 250KHz, 200KHz, 100KHz, 50KHz, 25KHz;
Data upload real-time, the max of the depth of the collection is 10T, far from the practical need.