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TM1637 display/What is in your box/05. The first number
What is in your box · 05 of 13

The first number

Four wires, one library from the Library Manager, and a dozen lines of sketch that put 1234 on the display and then count. On an Uno feed it 5V; on an ESP32 feed it 3V3, because the board's pull-ups put VCC on the two signal wires.

Updated 2026-09-256 min readTM1637 display

Install the library

In the Arduino IDE, open Tools → Manage Libraries, search for TM1637 and install the one by Avishay Orpaz. The header it gives you is TM1637Display.h.

There are at least six libraries called some variation of TM1637, and they do not share function names. Sketches from elsewhere that call display.show() or tm.displayStr() belong to different ones and will not compile against this.

Four wires

Four wires
Arduino Uno
Your board
The two signal wires
CLOCK (CLK)
D2
DATA (DIO)
D3
VCC
5V
GND, VCC, CLOCK, DATA — and the pin order is the same at both ends of the board. Any two digital pins will do for CLOCK and DATA; these are the ones the sketches use, and they avoid every pin your board needs for itself. The library is told them in that order: TM1637Display display(2, 3); — CLOCK first. VCC is the one worth a thought: it is 5V here, and it decides what voltage the two signal wires sit at, because the board’s 10 kΩ resistors pull them up to it.
DisplayArduino UnoESP32ESP32-S3
GNDGNDGNDGND
VCC5V3V33V3
CLOCKD2GPIO 18GPIO 4
DATAD3GPIO 19GPIO 5

Any two digital pins work for CLOCK and DATA; these avoid the pins each board needs for itself. VCC is the one that is not free choice: the board's pull-ups tie both signal wires to it, so on a 3.3 V board it goes to 3V3.

Run it

Set Tools > Board to your board and Tools > Port to the one that appears when you plug it in; on an ESP32-S3 also set Tools > USB CDC On Boot to Enabled. The sketch's opening comment lists the same rows, so a copy that travels without this page still carries them.

Upload it. You should get 1234 for two seconds, then a count.

Three lines are worth pointing at.

TM1637Display display(CLOCK_PIN, DATA_PIN) takes clock first. Both are plain digital pins, so the wrong way round is not an error anybody's compiler can catch — it is a dark display.

setBrightness(4) does not send anything on its own. The brightness rides along with the next lot of digits, which is why it is called before showNumberDec and not after. Called on its own in a sketch that never shows anything again, it appears to do nothing at all.

showNumberDec(i) writes all four digits and blanks the ones it does not need, so 7 appears as three blanks and a 7 rather than 0007. Passing true as the second argument gives you the leading zeros instead — and for a clock you will want them, for a reason that only shows up at midnight.

Then unplug the board

With the count running, pull the USB cable and plug it back in. The display comes up blank and stays blank until setup() runs again — nothing is stored in the display across a power cut.

Now try it the other way: while the count is running, press the reset button and watch. The number on the display at the moment of the reset stays there until the sketch writes a new one. The chip does not know or care that the board driving it has restarted, which is the whole point of the previous two articles and something to remember when a display looks perfectly alive and the sketch behind it is not.

The code

Shows 1234, waits, then counts 0 to 60 twice a second. Change the two pin numbers for your board; nothing else in it is board-specific, and the display behaves the same on all three.

first_number.ino
/*
  TM1637 4-Digit Display - the first number        TK51 / /p/tk51

  Wiring. No pad on this board is square, so go by the names
  printed on the back: GND, VCC, clock, data. Seen from the
  display side with the header on the left, GND is the top pin.

    GND   -> GND
    VCC   -> your board's logic supply: 5V on an Uno, 3V3 on an
             ESP32 or ESP32-S3. Never 5V beside a 3.3 V board:
             the pull-ups would put 5 V on your pins.
    CLOCK -> D2 on an Uno, GPIO 18 on an ESP32, GPIO 4 on an
             ESP32-S3
    DATA  -> D3 on an Uno, GPIO 19 on an ESP32, GPIO 5 on an
             ESP32-S3

  Arduino IDE
    Tools > Board            your board, e.g. Arduino Uno
    Tools > Port             the one that appears when you plug in
    Tools > USB CDC On Boot  Enabled   (ESP32-S3 only)
    Library: "TM1637" by Avishay Orpaz, from Tools > Manage
    Libraries. It installs TM1637Display.h.
*/

#include <TM1637Display.h>

#define CLOCK_PIN 2    // Uno D2.  ESP32: 18.  ESP32-S3: 4.
#define DATA_PIN  3    // Uno D3.  ESP32: 19.  ESP32-S3: 5.

// CLOCK first, then DATA. The wrong way round is a dark display.
TM1637Display display(CLOCK_PIN, DATA_PIN);

void setup() {
  display.setBrightness(4);     // 0 to 7, sent with the next write
  display.showNumberDec(1234);  // stays there with no further help
  delay(2000);
}

void loop() {
  for (int i = 0; i <= 60; i++) {
    display.showNumberDec(i);   // leading zeros off: 7 is "   7"
    delay(500);
  }
}

If it stays dark, swap CLOCK and DATA: crossed over, they look exactly like a dead board and damage nothing. If the count runs but the first digit stays blank on 0 to 9, that is showNumberDec blanking the digits it does not need, which is what it is meant to do.

View on GitHub · blocks/tk51-tm1637-display/arduino/first_number/first_number.ino @ v1.13

When it does not work

The display stays completely dark

In order: is GND connected, is VCC connected, and are CLOCK and DATA the right way round? Crossed signal wires are the usual answer and are harmless — the chip never sees a start condition, so it ignores everything. Then check the two pin numbers in the sketch match the two wires.

It compiles but nothing happens on an ESP32

Check VCC is on 3V3 and not 5V. It will often appear to work from 5V, which is the problem: the board's pull-ups then hold CLOCK and DATA at 5 V against pins Espressif rates for 3.3 V. Nothing may fail at once, which is why it goes unnoticed.

The serial port does not appear on my ESP32-S3

Set Tools > USB CDC On Boot to Enabled and upload again. This sketch prints nothing, but the next ones do, and without that setting the S3's USB port brings up no serial port at boot.

TM1637Display.h: No such file or directory

The library is not installed, or a different TM1637 library is. Search the Library Manager for TM1637 and install the one by Avishay Orpaz — several others exist with different function names, and code written for one will not compile against another.

The count is visible but very dim

Either the brightness is low — try setBrightness(7) — or the panel is a blue or white one on 3.3 V, which is a supply problem rather than a code one. Red, orange and yellow panels are the bright ones at 3.3 V.

Alongside this page
Installing the Arduino IDE and ESP32 board supportWhy 5 V on a 3.3 V pin is the mistake to avoid
Where this goes next

How a digit is stored, and how to write the things that are not digits.

Seven segments, one byte →

Edit this page — content/books/tm1637-display/the-first-number.mdx

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