These TM1638 modules are available very cheaply from sites such as eBay, AliExpress, and Banggood, and are ideal for displaying a value from a sensor or calculation:
They use an SPI protocol, and you write to the displays by sending a sequence of bytes to the displays. However, they are slightly cumbersome to drive because each byte in the stream sets the state of a single segment in all the displays.
Connect the display using the appropriate SPI pins as follows:
|Pin||Connection||Arduino Mega 2560|
The third column shows the pins I used when testing the program on an Arduino Mega 2560. You can use any suitable pin as the Enable pin; specify it with this defvar:
(defvar en 10)
The following routine on turns on the display and sets the brightness; the parameter can be from 0 (dimmest) to 7 (brightest):
(defun on (bri) (with-spi (str en 1000 0 2) (write-byte (+ #x88 bri) str)))
The following list gives the segment definitions for the digits 0 to 9 and the hexadecimal digits A to F:
(defvar seg '(#x7e #x30 #x6d #x79 #x33 #x5b #x5f #x70 #x7f #x7b #x77 #x1f #x4e #x3d #x4f #x47))
This routine clr clears the display:
(defun clr () (with-spi (str en 1000 0 2) (write-byte #x40 str)) (with-spi (str en 1000 0 2) (write-byte #xC0 str) (dotimes (n 16) (write-byte 0 str))))
Finally this routine put writes eight digits to the display:
(defun put (dp &rest dig) (with-spi (str en 1000 0 2) (write-byte #x40 str)) (with-spi (str en 1000 0 2) (write-byte #xc0 str) (dotimes (n 7) (let ((byt 0)) (dotimes (c 8) (setq byt (logior (ash (logand (ash (nth (nth c dig) seg) (- n 6)) 1) (- 7 c)) byt))) (write-byte byt str) (write-byte 0 str))) (write-byte (ash 1 (- 7 dp)) str)))
The first parameter specifies the decimal point position, from 0 to 7, or 8 for no decimal point.
The remaining eight parameters specify the number to show on each display. For example, to display “0123.4567” give the command:
(put 3 0 1 2 3 4 5 6 7)
Reading the keypad is left as an exercise for the reader.