Reaction Timer

This is another school project, a simple circuit used for practising troubleshooting.

I cannot release the schematics as they are not mine to give.

How it works: this circuit simply measure the time it takes to release the first button and press the second one. When the first push button is pressed, the timer is reset (and the buzzer sounds). As soon it's released, the timer starts counting and it will stop when the second push button is pressed. On the displays we can see the time.

Here's a short demo:

The main components are 4 chips : a 74LS76 (Dual JK Flip-Flop), a 74LS10 (triple 3 input NAND gate) and two 74LS90 (Counter).

That big trainer you see, where the breadboard is attached is once again a school project. In our very first semester we had to build one of these babies here, from bending the metal to soldering all the components.
It's then used throughout the whole course for several other units.