This kit creates an interesting visual effect of a "lighted" ball (LED) swinging between left & right continuously. The "ball" emits green light as it goes from left to right and changes to red on its way back. The LED used in this kit has 3 terminals and it can produce red & green light. Transistors (Q1 & Q2) form a transistor-transistor astable circuit that generates square wave which we use to increment the decade counter IC ( IC1). The 10 outputs of IC1 switches to logic high sequentially & continuously (from 0-- 9) as the counter is running. The running speed of the LEDs can be varied by adjusting the trim pot (preset) VR1.