ESP32-C3 + OLED with U8g2

From an empty folder to text and graphics on a small I²C OLED, with the display driver and the fonts chosen before the build. Written for an ESP32-C3 with 4 MB flash; every other ESP32 works the same way (change the target in step 2 and the pins in step 5).

U8g2 is optional and not in the release firmware, so this is your own ESP-IDF build. If you have never built MicroCS for an ESP32, skim ESP32 from zero first.

1. What you need

• ESP-IDF 5.x (Espressif's installer or the VS Code ESP-IDF extension), Python 3, git.
• Your OLED's controller and size, and the two GPIOs it is wired to:

OLED	U8g2 display name
0.96" 128×64 (the most common one)	ssd1306_i2c_128x64_noname
1.3" 128×64	sh1106_i2c_128x64_noname
0.91" 128×32	ssd1306_i2c_128x32_univision
ESP32-C3 "SuperMini" / "0.42 inch OLED" boards (72×40, built in)	ssd1306_i2c_72x40_er — usually SDA = GPIO5, SCL = GPIO6

Wiring: OLED VCC → 3V3, GND → GND, SDA / SCL → two free GPIOs. On the C3, GPIO 4/5 or 5/6 are good choices; avoid GPIO 2, 8 and 9 (strapping pins) and 11–17 (flash).

2. Create the project

git clone https://github.com/amir1387aht/MicroCS
cp -r MicroCS/ports/esp32/example my_oled && cd my_oled
git clone https://github.com/amir1387aht/MicroCS components/MicroCS
idf.py set-target esp32c3

The example already fits a 4 MB flash: 2 MB for the program (Wi-Fi and TLS included) and ~1.9 MB for your scripts and font files.

3. Get the u8g2 sources (pick one)

• Easiest: let the build download u8g2 2.37.1 once — CONFIG_MICROCS_U8G2_DOWNLOAD=y in step 4.
• Offline: python3 components/MicroCS/tools/u8g2.py fetch (found automatically afterwards).
• Your own copy: CONFIG_MICROCS_U8G2_DIR="/full/path/to/u8g2" in step 4.

If none of them is there, the build stops and prints these three options.

4. Turn U8g2 on, choose the display and the fonts

Append to sdkconfig.defaults:

CONFIG_MICROCS_U8G2=y
CONFIG_MICROCS_U8G2_DOWNLOAD=y
CONFIG_MICROCS_U8G2_DISPLAYS="ssd1306_i2c_128x64_noname sh1106_i2c_128x64_noname"
CONFIG_MICROCS_U8G2_FONTS="6x10_tf helvB10_tr logisoso24_tn open_iconic_embedded_1x_t"
CONFIG_MICROCS_U8X8_FONTS="chroma48medium8_r"

• Displays: only the listed ones are compiled in (1–3 KB of flash each). Without the line you get SSD1306 128×64 / 128×32 and SH1106 128×64.
• Fonts: built into the flash; the first one is the default. Without the line you get six small fonts (~7 KB).
• Names and sizes: python3 components/MicroCS/tools/u8g2.py displays ssd1306, python3 components/MicroCS/tools/u8g2.py fonts helv.
• Delete an existing sdkconfig — sdkconfig.defaults is read only when there is none. (The same settings are in idf.py menuconfig → Component config → MicroCS → U8g2 displays.)

5. Give I²C its pins

In main/main.c, one line after MCS_ESP32_CFG_DEFAULT:

mcs_esp32_cfg_t pins = MCS_ESP32_CFG_DEFAULT;
pins.i2c[0] = (mcs_esp32_i2c_pins_t){ 5, 6 };   // SDA, SCL - your GPIOs
mcs_esp32_hal_init(&hal, &pins);

Since MicroCS 1.12 you can also skip this step and choose the pins from C#, before the first I²C call: I2C.Open(0, new I2cConfig(400_000, 5, 6)); (SDA, SCL — see peripheral settings).

6. Build and flash

idf.py build flash monitor

Press Enter for the > prompt and check that the display driver is there:

> Console.WriteLine(string.Join(",", U8g2.Displays));
ssd1306_i2c_128x64_noname,sh1106_i2c_128x64_noname
> Console.WriteLine(string.Join(",", I2C.Scan(0)));
60

60 = 0x3C, the OLED. (Ctrl-] leaves the monitor.)

7. The first program

main.cs:

var oled = new U8g2("ssd1306_i2c_128x64_noname");   // I2C bus 0, address 0x3C
oled.Begin();
int n = 0;
while (true) {
    oled.ClearBuffer();
    oled.SetFont("helvB10_tr");
    oled.DrawStr(0, 14, "Hello ESP32-C3");
    oled.SetFont("logisoso24_tn");
    oled.DrawStr(0, 56, n.ToString());
    oled.DrawFrame(0, 0, 128, 64);
    oled.SendBuffer();
    n++;
    Thread.Sleep(500);
}

Upload it as /main.cs (runs at every boot):

python3 components/MicroCS/tools/mcs_remote.py --port /dev/ttyACM0 put main.cs /main.cs + run /main.cs

(--port COM5 on Windows.) Or MicroCS Studio in Chrome/Edge: Connect → paste → Save & Run.

8. More fonts without rebuilding

All 2000+ u8g2 fonts work from files. Extract the ones you want on the PC:

python3 components/MicroCS/tools/u8g2.py extract profont12_tr unifont_t_symbols -o fonts

copy them into /fonts on the board:

python3 components/MicroCS/tools/mcs_remote.py --port /dev/ttyACM0 mkdir /fonts + \
    put fonts/u8g2_font_profont12_tr.bin /fonts/u8g2_font_profont12_tr.bin

and use them like a built-in font: oled.SetFont("profont12_tr"); — the built-in copy if there is one, otherwise the file is loaded.

9. Next steps

• Text only, almost no RAM: var t = new U8x8("ssd1306_i2c_128x64_noname"); t.Begin(); t.DrawString(0, 0, "Hi");
• Less RAM for U8g2: add _1 to the name ("ssd1306_i2c_128x64_noname_1") and draw in oled.Draw(() => { ... }); (page mode).
• Buttons and menus: oled.Begin(selectPin, nextPin, prevPin) + UserInterfaceSelectionList(...) (examples/u8g2/menu.cs).
• Sensor values on the screen: examples/u8g2/sensor_log.cs.
• Ready-made scripts: MicroCS Studio → Templates → U8g2 displays (20 examples: shapes, fonts, bitmaps, menus, dashboard, clock, U8x8 ...).
• Try it on the PC first: make fetch-u8g2 mcs-u8g2 && ./build/mcs_u8g2 --oled main.cs.
• The whole API: U8G2.md.

Troubleshooting

Symptom	Fix
black screen, no error	address 0x3D: U8g2.I2C("ssd1306_i2c_128x64_noname", 0, 0x3D); SDA/SCL swapped; no 3V3
picture shifted by 2 pixels / noise on the right	it is an SH1106: use sh1106_i2c_128x64_noname
I2C.Scan(0) is empty	wiring, or the wrong GPIOs in step 5
I2C.Scan: not supported (or I2C.Write: …)	step 5 missing — the bus has no pins (or open it with new I2cConfig(400_000, sda, scl))
U8g2 does not exist	U8g2 is not in the firmware: step 4 (and delete sdkconfig), rebuild
build stops: "u8g2 sources not found"	step 3
display '…' is not compiled in	add it to CONFIG_MICROCS_U8G2_DISPLAYS, rebuild