Reaction Testing Game using Interrupts and Arduino

The interrupts provided by the AVR microcontroller can be used for various purposes. Many applications can be made by using the ISR.

Fig. 1: Prototype of Arduino based Reaction Time Game

This feature of the AVR microcontroller will be used to make an LED following game which will test a user’s reaction time. There will be 4 LEDs and 4 corresponding buttons for each. After the game begins, a timer will start and a random LED will glow. The user will then have to press the button corresponding to that LED to turn it off. If the correct button is pressed, another LED will glow-up but if the wrong button is pressed, a penalty will be added and the same LED will continue to glow till the correct button is pressed. This will be repeated for a total of 5 turns. Player one will complete his turn and his time will be displayed and the second player will play.. At the end of the game, player with minimum time will be declared as the winner.

Description:

16X2 LCD is used in 4 bit mode to provide the user interface. The upper 4 bits are first sent to the LCD followed by the lower 4 bits and the final result will be printed There will be 5 buttons – one for starting the game, and the other four for connecting LEDs.

The basic idea is that whenever the TCNT of the AVR microcontroller reaches a certain number, an interrupt will be generated. The max TCNT value can be modified to change the time after which the ISR runs and checks for the interrupt condition.

Now that the microcontroller is set for external interrupts, pressing any button will generate one. That interrupt will then be looked for in the vector table of the microcontroller.

Time of the players will be counted using CTC mode setting WGM12 in TCCR. F_CPU = 16000000 so set OCR1A = 16000 and prescaler = 1. Every time the TCNT reaches 16000, 1ms has passed and TCNT is reset. So, interrupt takes place every 1ms and player time increases every millisecond.

To tackle button debouncing, give a delay using _delay_ms() function. Button debouncing is the hardware issue in the state of switching from one state to the other. This may cause interrupts to be executed even when they are not programmed to. Debouncing can be tackled by giving a 10ms delay.

Pin Connections:

Port B and D of the Arduino are used to connect the LCD. Port B is used for connecting the EN and RS and Port D for connecting the 4 data bits.

LCD Pin Connections will be as follows:

(LCD Pin – Arduino Pin)

1) RS – PB2

2) EN – PB3

3) Vcc – 5v

4) Vee – Gnd

5) Vss – Gnd

6) DB4 – PD4

7) DB5 – PD5

8) DB6 – PD6

9) DB7 – PD7

Button Connections:

All the five external interrupts – PCINT0, PCINT1, PCINT2, INT0, INT1 will be used since there are 5 buttons and an independent interrupt needs to be generated for all the five buttons. The 5 buttons (push/switch) will then be connected to the following 5 pins of the Arduino as per following diagram.

> PD0 or PCINT16

> PB0 or PCINT0

> PD2 or INT0

> PD3 or INT1

> PC4 or PCINT12 (for start)

Fig. 2: Pin Diagram of Arduino Uno

Code:

The code does all the following:

1) GiveCommand() function is used to send command to the LCD and GiveData() for sending data to the LCD. For example to send a clear LCD command 0x01 is sent using the GiveCommand() function.

2) The Init function is used to set all the pre-requisites such as :

– Setting the prescaler equal to 1 by enabling WGM (wave generation mode) and CS10 by writing (1<< WGM12)|(1 << CS10)

– Initializing the LCD in 4 bit mode

– Enabling all bits required to enable the interrupt service.

3) The SendString() function simply tells what message needs to be printed.

4) The Instruction() and Data() functions tell whether the LCD is working in instruction mode or data mode.

5) Itoa() function will be used to convert an integer to a string.

6) clk() function provides the clock required using enable (EN) high or low.

7) The ISR() function is to specify what needs to be done when an interrupt condition is true.

– PCINT0_vect, PCINT1_vect, PCINT2_vect, INT0_vect are arguments corresponding to the buttons chosen above. These tell the microcontroller where to find a certain interrupt in the vector table.