Digital transistor-to-transistor logic (TTL) signals use voltage levels between 0 and 0.4 V to represent binary 0 and voltage levels between 2.4 and 5 V to represent binary 1. Develop a simple circuit that uses a BJT to switch on and off an LED using a TTL trigger at these digital voltage levels. Assume that the LED resistance is 10 Ω and the current required by the LED to generate the required brightness is close to (but not more than) 40 mA. Also assume that an npn BJT and a 10 V dc power supply are available. Also, a current limiting resistor of 20 kΩ is available for the base of the BJT and a resistor of 200 Ω is available in series with the power supply and the LED. Indicate a practical application of this device.