7.9 KiB
TM1637
Library for TM1637 driven displays and keyscans.
Description
The TM1637 drives 7 segment displays and can also scan a 16 key keyboard.
Library is tested with Arduino UNO and a 6 digits display.
ESP32 is supported since 0.2.0 see https://github.com/RobTillaart/TM1637_RT/pull/5
Interface
- TM1637() constructor
- void init(uint8_t clockPin, uint8_t dataPin, uint8_t digits = 6) set up the connection of the pins to the display. As the display is only tested with a 6 digit display, this is used as the default of the digits parameter.
- void displayRaw(uint8_t * data, uint8_t pointPos) low level write function.
- void displayInt(long value) idem
- void displayFloat(float value) idem
- void displayHex(uint32_t value) idem
- void displayClear() writes spaces to all positions, effectively clearing the display.
- void setBrightness(uint8_t b) brightness = 0 .. 7 default = 3.
- uint8_t getBrightness() returns value set.
- uint8_t keyscan(void) scans the keyboard once and return result. The keyscan() function cannot detect multiple keys.
displayRaw() can display multiple decimal points, by setting the high bit (0x80) in each character for which you wish to have a decimal lit. Or you can use the pointPos argument to light just one decimal at that position.
displayRaw() can display some of the alphabet as follows:
- space (blank) is 0x10
- '-' (minus) is 0x11
- a-f are coded as 0x0a-0x0f
- g-z are coded as 0x12-0x25. Characters that cannot be represented in 7 segments render as blank.
So "hello " is coded as 0x13, 0x0e, 0x17, 0x17, 0x1a, 0x10
See routine ascii_to_7segment() in the example TM1637_keyscan_cooked.ino. It presents a more convenient interface for displaying text messages on the display.
Routine button_poll() in the same example shows one way of polling and de-bouncing button presses.
Display support
The library is tested with a 6 (=2x3) digit - decimal point - display and a 4 (=1x4) digit - clock - display. At low level these displays differ in the order the digits have to be clocked in. To adjust the order for a not supported display, the following function can be used with care:
- void setDigitOrder(uint8_t a, uint8_t b,... uint8_t h) sets the order in which up to 8 digits should be clocked in.
If you have a (7 segment) display that is not supported by the library, please open an issue on Github so it can be build in.
Tuning function
To tune the timing of writing bytes.
- void setBitDelay(uint8_t bitDelay = 10)
- uint8_t getBitDelay()
Tuning minimum pulse length
The class has a conditional code part in writeSync to guarantee the length of pulses when the library is used with an ESP32. The function called there nanoDelay(n) needs manual adjustment depending upon processor frequency and time needed for a digitalWrite. Feel free to file an issue to get your processor supported.
Keyboard Scanner usage and notes
Calling keyscan() returns a uint8_t, whose value is 0xff if no keys are being pressed at the time. The TM1637 can only see one key press at a time, and there is no "rollover". If a key is pressed, then the values are as follows:
| keyscan results are reversed left for right from the data sheet. | |||||||||
| pin | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | |
|---|---|---|---|---|---|---|---|---|---|
| name | sg1 | sg2 | sg3 | sg4 | sg5 | sg6 | sg7 | sg8 | |
| 19 | k1 | 0xf7 | 0xf6 | 0xf5 | 0xf4 | 0xf3 | 0xf2 | 0xf1 | 0xf0 |
| 20 | k2 | 0xef | 0xee | 0xed | 0xec | 0xeb | 0xea | 0xe9 | 0xe8 |
To modify a "generic" TM1637 board for use with a keyboard, you must add connections to either or both of pins 19 and 20 (these are the "row" selects) and then to as many of pins 2 through 9 (the "columns") as needed. It is easiest to connect to the "column pins" (2-9) by picking them up where they connect to the LED displays (see second photo). Generic keyboards that are a 4x4 matrix won't work; the TM1637 can only scan a 2x8 matrix. Of course, fewer keys are acceptable; I use a 1x4 keyboard in my projects.
Further, the TM1637 chip needs a fairly hefty pull-up on the DIO pin for the keyscan() routine to work. There is no pull-up in the TM1637 itself, and the clone boards don't seem to have one either, despite the data sheet calling for 10K ohms pull-ups on DIO and CLOCK. 10K is too weak anyway. The slow rise-time of the DIO signal means that the "true/high" value isn't reached fast enough and reliably enough for the processor to read it correctly. The new pull-up reduces the rise time of the signal, so that true/high values are achieved in a few microseconds. I find that a 1K (1000) ohm resistor from DIO to 3.3 v works well. This is perfect with a 3.3 volt processor like the ESP8266 or ESP32, and a 5V Atmega 328 ("Arduino UNO") family processor is happy with that as well.
The TM1637 boards want to be run off of 5 volts, regardless of what the processor voltage is. Their logic levels are compatible with 3.3 volt processors, and they need 5 volts to make sure the LEDs light up.
The unmodified generic TM1637 board (front and back).
The modified generic TM1637 board with connector for 1x4 keyboard. The blue wire is bringing out pin 19 (k1). Four segments/columns are picked up from the LEDs.
The 4 button keyboard plugged into the TM1637 board.
Scope photo showing slow rise time of DIO pin (upper trace) on the unmodified TM1637. The lower trace is the CLK. The 8 fast CLK pulses on the left represent the 0x42 command to read keyboard being sent to the TM1637.
Scope photo showing faster rise time of DIO pin (upper trace) with 1000 ohm pull-up on DIO. In both scope photos, the F5 key is pressed; the bits are least significant bit (LSB) first, so read as 10101111 left to right.
The scope photos were taken using the TM1637_keyscan_raw example, with the scope trigger hooked to the TRIGGER pin, and the two channel probes hooked to DIO and CLK. Vertical sensitivity is 2v/division, horizontal timebase is 20usec/division.
Keyscan
Implemented in version 0.3.0 Please read the datasheet to understand the limitations.
// NOTE:
// on the TM1637 boards tested by @wfdudley, keyscan() works well
// if you add a 910 ohm or 1 Kohm pull-up resistor from DIO to 3.3v
// This reduces the rise time of the DIO signal when reading the key info.
// If one only uses the pull-up inside the microcontroller,
// the rise time is too long for the data to be read reliably.
Operation
See examples
Future
- elaborate documentation
- testing
- rename init() to begin() ?
- keyScan() camelCase ?
- separate CHANGELOG.md