Reaction Time Tester Engineering Kit with Circuit Diagram (No Soldering Required) DIY Electronic Kit Metal Sensing Detector MINI Handheld DIY Soldering 10 Best Circuit Design Learning Kits to Spark Your Creativity and Make: Electronics Book Experiment 18 Reaction Tester YouTube. The Reaction Tester is based around the 555 timer IC. The kit is designed to test and expand one's sense of timing. The students need to synchronize their reaction time to press the button in time to keep the LED lit or else it goes out. Note: Step by step instructions are not included use the included parts list to identify the components and assemble according to the included circuit diagram. Jumper wire not included (breadboard accepts 21 to 26 AWG wire).