The CircularBuffer class should implement a buffer of 32 elements with the following methods:

• write: add an element to the end of the buffer. Check if the buffer is full before writing and set the overrun flag if this is the case
• available: check if new data have arrived in the buffer
• read: read data from the buffer if it is not empty
• is_full: tells if the buffer is full
• overrun: tells if an overrun error has occurred in the past
• clr_overrun: clear the overrun flag
• flush: clears the buffer

Exercise 4:

Read the keypad in an interrupt driven routine. Keep the pressed keys in the circular buffer written in exercise 3.

Write a test program that starts the interrupt driven keypad driver and reads data from the circular buffer in rather large intervals (e.g. every 5s or 10s)

Exercise 1:

Scan the keyboard in intervals of 100 ms and print the key that is pressed. This will result in printing the key as long as it is pressed.

Exercise 2:

Wait until the key is released and only the print the key. This will result of a single key value for each button press.

Exercise3:

Read the keypad in an interrupt driven routine. Keep the pressed keys in a circular buffer. Add the following methods:

• available: returns true if at least 1 character is in the buffer
• read: read a character and remove it from the circular buffer
• status: return an overrun error if the circular buffer is full and a pressed key has been missed
• flush: clear the circular buffer

• create a table with the led setting of the seven segments for all hex digits and a clear digit (all segments off). dp means decimal point, which is only used on the second digit, where it controls the following colon.

• start_transfer: implements the start sequence (dio going low when clk is high)
• stop transfer: implements the "end of transfer" sequence (dio going high when clk is high)
• write_bit: write a single bit: with clk low, set dio to the bit value, then send a pulse (high followed by low) on the clk pin
• write byte: send 8 bits. After the eights bit, check the acknowledge signal. Switch dio to input, check acq, switch dio back to output after the falling edge of the nineth clock pulse
• display on: switch the display on: start_transfer, send display_on command, stop transfer
• create a table with the led setting of the seven segments. dp means decimal point, which is only used on the second digit, where it controls the following colon.

      A
     ---
  F |   | B      dp,g,f,e, d,c,b,a: the data byte
     -G-
  E |   | C
     ---
      D

• write_digit(digit_num,digit,colon=False): sets digit number digit_num to the value digit. If colon is true and the digit number is 1 (start counting from zero) the switch the colon on.
• clear_digits(colon=False): clear all digits. Only the colon stays on if colon == True
• write_hex(number,colon=False): write a hex number to the display
• write_dec(number,colon=False): write a decimal number to the display.

Seven Segment Display and Keypad

The Seven Segment Display and its TM1637 controller

There is a nice and simple seven segment display controlled by a TM1637 controller, which can be used e.g. as a clock display. It provides 4 digits and a colon dividing digits 1 and 2 from digits 3 and 4, such that the first two digits can be used to display hours, the last two digits to display minutes and the colon can be set blinking at a 1 Hz rate. Of course you can also use it for other purposes like displaying the voltage values of a voltmeter.

As can be seen from the back view of the module, interfacing to the ESP32 is pretty simple. Here are the connections I use:

https://www.mcielectronics.cl/website_MCI/static/documents/Datasheet_TM1637.pdf

The TM1637 uses a proprietary 2-wire serial protocol with a data line (dio) and a clock line.

Exercise 1:

Carefully read the data sheet.

Write a driver implementing the serial protocol. Check the acknowledge signal from the controller to make sure the data have been correctly transmitted. The signals on the dio and the clk lines must be programmed setting the corresponding GPIO pins. Serialization is also done in software.
Write a test routine that displays 1234 on the seven segment digits.

Exercise 2:

Modify exercise 1 to implement a blinking colon

Exercise 3:

Read the current time from the ntp and implement a clock displaying hours and minutes. Make the colon blink at a 1 Hz rate.

The Keypad

The keypad has a total of 16 switches. These are connected to 8 pins organized as 4 rows and 4 columns.

Set the first row pin to low and check on each column pin if you read a zero. If you do, you have found the switch closed. If not, continue the same procedure on the other row pins.

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