Clockulator

Two clocks, side by side: local time and UTC. Turn a dial and both move together, so you can read a moment in both zones at once.

It answers four questions:

1. What time is it right now?
2. What time is it UTC right now?
3. When it is timeX here, what time is it UTC?
4. When it is timeX UTC, what time is it here?

Two builds, for different hardware. They share the idea, not the code.

ClockSpin — ESP8266

The original. Two TM1637 4-digit displays, a rotary encoder, and a button.

• Local time on one display, UTC on the other
• The knob offsets both, ten minutes per detent
• Press the knob, or leave it ten seconds, to return to the present
• Hold the knob while powering on to re-run the WiFi config portal

Libraries: WiFiManager, NTPClient, Time, Timezone, ESPRotary, Button2, Grove 4-Digit Display.

Clockulator — ESP32-S3

A port to a Waveshare ESP32-S3-LCD-1.3: one 240x240 ST7789 panel viewed through a prism, and a QMI8658 6-axis IMU. No knob, no buttons, so every control is a gesture.

• UTC on the top half of the panel, local time below
• Tilt and hold to scroll time, aeroplane-style: tilt angle sets the rate, and time keeps moving until you level it off. The curve is quadratic, so small tilts give fine control and full deflection covers hours
• Tap it flat on the desk to return to the present
• Tap its left or right edge on the desk to change timezone (see zones.h)
• Hold it face-down for three seconds to open the WiFi config portal
• Ten seconds untouched also returns to the present
• The digits carry a slow colour shimmer keyed to the time of day

Timezone selection persists across reboots. Credentials come from WiFiManager's captive portal and live in NVS, so there is no secrets file.

Libraries: WiFiManager, TFT_eSPI, SensorLib. NTP and DST come from the ESP32 core's own configTzTime() and POSIX timezone strings, which replaces the NTPClient/Time/Timezone stack the ESP8266 build needs.

Notes for this hardware

The sensor and display constants in gestures.cpp were measured on the device rather than taken from datasheets, and two of them are worth knowing about:

• Thresholds are multiples of measured gravity, never absolute g. The QMI8658 does not reliably honour the accelerometer range it is configured with -- asking for +-8g has been observed reading half scale, varying with what state the chip was left in. Ratios are immune to this; absolute thresholds are not.
• Tilt is read about the X axis, taps are classified by impulse direction. Striking an edge on the desk registers 7-9g on X (sign gives the side) while a flat tap registers on Z. Tapping the side in situ, without lifting the device, is too weak to separate from handling noise.

TFT_eSPI needs two fixes for the ESP32-S3 that live in the library, not here: USE_FSPI_PORT in User_Setup.h, and dropping the S3 from the MISO-to-MOSI aliasing block in Processors/TFT_eSPI_ESP32_S3.h. Without the first, tft.begin() crashes with StoreProhibited; without the second, it hangs for ever on the SPI busy flag.