This circuit uses LEDs to display logic states for high, low, rising pulse, and falling pulse, it is generally useful for debugging logic circuitry.This circuit can monitor TTL logic levels. TTL compatible CMOS logic families can also be monitored.This circuit can be built on perforated circuit board and wired by hand. The completed circuit can be assembled into a clear plastic box with the wires protruding out one end. The LEDs should be visible through the box. IC sockets should be used for easy chip replacement. source

The purpose of this project was to create a useful yet easy to build Logic Analyzer that would provide much of the functionality of a real Logic Analyzer. The biggest drawback that the computer has is its sampling rate. The program was written on a 75 MHz Pentium computer which provided accurate sampling rates up to 10 kHz. Although this doesn’t match the speed of real Logic Analyzers, this should be sufficient speed to be useful for many projects. source

This circuit is a simple TTL Logic Probe. It used to indicate the logic state of the node of any TTL logic circuit.The circuit use small components count.It just need 1×74LS00 , 1×74LS47 , 1×7-Segment,2xLEDs and some of passive components.source