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My last forum code example contribution was about a year ago, and provided sample code for the TM1637 7-Segment LED driver/controller. The TM1637 is used on 4-digit 7-Segment display modules available from a variety of Asian sources online. Two module varieties are available -- 7-Segment with decimal point and 7-Segment with semicolon. The semicolon version is commonly found as the display on digital clocks and microwave ovens. My interest in this display module was its ideal suitability for displaying the revolutions per minute (RPM) for a small engine tachometer device I designed. Having completed this device, I began experimenting with other segment type displays and with the keyboard scan function available on the TM1637. Thereafter, I posted a code sample for the TM1637 4 digit display module and 16 button keypad that provided the primitive task of displaying the key number 01 through 16 on the 4-digit display.
Curiosity led me to acquire some keyboard/display modules, including the 'LED&KEY' and the 'HCW-132', both easily found and acquired from several online sources. Both of these modules use the TM1638 LED driver/controller instead of the TM1637. While similar, the TM1638 differs in several respects:
- the TM1638 uses a 3-wire interface (similar to SPI) featuring clock, data and strobe signal (the TM1637 uses a 2-wire interface for clock and data)
- the TM1638 accommodates up to 8 digits, while the TM1637 is limited to 6 digits
- the TM1638 is compatible with either common anode or common cathode 7-segment displays, while the TM1637 is common anode only
- the TM1638 accommodates up to 10 segments/digit while the TM1637 accommodates up to 8 segments/digit
- the TM1638 accommodates up to 24 input keys, while the TM1637 accommodates up to 16 input keys.
The first of the two keyboard/display modules, the 'LED&KEY' is relatively straight forward inasmuch as its 7-Segment displays are common anode wired. The module (as shown is the picture) has 8 push-button keys, 8 7-segment digits (plus decimal point), and 8 discrete LEDs. This array of features makes it potentially useful in practicable applications, and not just as an experimenter's learning or interface device.
The code sample provided here is fairly primitive in exercising each of the discrete LEDs, displaying the hex digits 0-9 and A-F, and then waiting for a key press. In response to a key closure, the corresponding 7-segment display shows the key number 1-8, and the discrete LED flashes the corresponding number of times. Pressing the 5th key, for example, displays '5' on the fifth digit location and causes the discrete LED to flash 5 times. If the key is held closed, the display action loops continuously.
The code is copiously commented and hopefully is clear in describing how characters are written to the 7-segment digits, and how the keypad is scanned. Further explanation of the sample code structure is included in the introductory header comments. A thorough review of the TM1638 data sheet is essential.
I've interfaced the LED&KEY module with the Microchip Curiosity Board equipped with a PIC16F18346 uC. Your development platform is probably different, so change the configuration 'INCLUDE' file at the beginning of the code, and re-specify the port pin assignments as necessary.
The other module, the 'HCW-132' is an entirely different creature in that its 7-segment displays are wired in common cathode mode. This variation transposes the digit positions 1-8 with the segment addresses 1-7 (not including the decimal point). I've written a sample code for this module also and will post it in a future contribution to this forum.
As always, comments, corrections and criticisms are welcome!