node32-gps-clock

A GPS-disciplined clock for a round 1.28" display. It shows local time, date, weekday and UTC. The time comes from a CN-06 (u-blox NEO-6M) GPS receiver, and a NodeMCU (ESP8266) drives the display.

        SATURDAY
       27/09/2026
     ·            ·
   ·   18:42:10     ·     <- local time, centered
     ·  UTC 21:42   ·
       FIX  SAT 7         <- fix status / satellites

A ring of 60 dots along the edge fills up as the seconds go by.

Features

• Local time HH:MM:SS, date DD/MM/YYYY, weekday and UTC HH:MM.
• Fixed UTC offset (default UTC-3, Brasília). Day, month and year rollover is handled.
• Smooth U8g2 fonts (Logisoso, Helvetica) without flicker. Each field is rendered into a small RAM canvas and pushed only when it changes, because the ESP8266 has no RAM for a 115 KB full-screen framebuffer.
• Clear on-screen states: waiting for GPS, no GPS data (wiring), no fix, fix.
• One-line GPS status per second on the serial monitor for troubleshooting.
• Wi-Fi turned off: it frees heap and keeps RF noise away from the GPS antenna.

Hardware

Part	Notes
NodeMCU v2/v3 (ESP8266, ESP-12E)
CN-06 GPS receiver (u-blox NEO-6M)	e.g. Crius CN-06. Any NMEA GPS should work.
GC9A01 round IPS display, 1.28", 240x240, SPI	Its SPI pins are often labeled SDA/SCL. It is not I2C.

Wiring

CN-06 GPS	NodeMCU
VCC	VIN (5V)	The module has its own regulator. 3V3 also works, with less margin.
GND	GND
TX	D6 (GPIO12)	SoftwareSerial RX
RX	not connected	Only needed to configure the GPS

GC9A01	NodeMCU
VCC	3V3
GND	GND
SCL	D5 (GPIO14)	SPI clock (fixed)
SDA	D7 (GPIO13)	SPI MOSI (fixed)
CS	D1 (GPIO5)
DC	D2 (GPIO4)
RST	D0 (GPIO16)
BLK	3V3	Or leave it open if the module has a pull-up

D3, D4 and D8 are ESP8266 boot strapping pins and are deliberately not used.

Build and upload

This is a PlatformIO project. The libraries are installed automatically:

• GFX Library for Arduino 1.4.9: GC9A01 driver and canvas
• TinyGPSPlus: NMEA parser
• U8g2: fonts only

pio run -t upload     # build and flash
pio device monitor    # serial monitor (74880 baud)

Set upload_port / monitor_port in platformio.ini to your port, or remove them for auto-detection.

Configuration

All settings are at the top of src/main.cpp:

Constant	Default	Meaning
UTC_OFFSET_MIN	-180	Local offset from UTC in minutes
GPS_BAUD	115200	GPS serial baud rate (the NEO-6M factory default is 9600)
GPS_ECHO_NMEA	false	Forward raw NMEA sentences to the serial monitor
STATUS_EVERY_MS	1000	Serial status interval

The screen layout (position, size and font of each field) is the fields[] table:

// top, width, height, font, layout reference
{ 97, 190, 46, u8g2_font_logisoso42_tn, "88:88:88", "", 0},   // HH:MM:SS

Fields are centered horizontally. Keep each field inside the seconds ring and within the 190x46 canvas (FIELD_MAX_W / FIELD_MAX_H).

Serial diagnostics

[GPS] chars=13194 ok=486 err=0 | sat=7 hdop=1.1 | FIX -23.03,-46.97 alt=690m | UTC 2026-09-27 21:42:10 (age 68ms)

Symptom	Likely cause
chars stays at 0	Nothing reaches D6: check the wiring (GPS TX -> D6), GND and power
chars goes up, ok=0, err goes up	Wrong baud rate, or the GPS is set to UBX binary only
ok goes up, sat=0, no fix	The GPS works; it needs open sky (a cold start can take minutes)

Notes and lessons learned

• SPI takes over D6. On the ESP8266, SPI.begin() switches GPIO12 to its MISO function. SoftwareSerial must be started after the display, or it never receives anything.
• The CN-06 may come preconfigured. Modules taken from drones are often set to 38400/57600/115200 baud and may not keep new settings (no flash on the NEO-6M, a dead backup battery, or an onboard EEPROM that won't write). This clock simply uses the baud rate the module already has.
• The time before a fix may be off by a few seconds. After a cold start, the NEO-6M can use a default leap-second value until it receives the UTC parameters, which can take up to ~12.5 minutes. The status line shows NO FIX in orange until then.
• The GFX library is pinned to 1.4.9. Newer releases target ESP32 Arduino core 3.x.