Question

We have a microcontroller (MCU) that operates at 3.3V. We want to connect a pushbutton switch to a digital input and a LED on a digital output. The pushbutton is normally open until pressed. The LED has a forward voltage of 2.3V at the operating current of 10mA. We want the input at the microcontroller to go high when the button is pressed. We want the LED to light up when the digital output is low Q5 Explain what two additional components are required for correct operation of the pushbutton on the digital input and the LED on the output. Choose appropriate values for both components, and explain your reasoning (a) Show on a circuit diagram how all these components should be connected to our MCU (b) (c) If the button is a doorbel, should we use software polling or an interrupt driven program on our MCU? Explain vour choice.

Answer 1

a. Components required: 10K Ohms Res. for pull up and down

330 Ohms resistance for LED current limiting

Power supply = 3.3V

Push button Switch

Microcontroller

b.

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c.

The digital IO connected to switch can be either polled or interrupt driven depending upon the application requirement.

In case of a door bell switch, the digital input/switch should be interrupt driven. As and when the door bell is pressed upon, the microcontroller is interrupted and respond to the door bell and return ack to its normal task.