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The TTGO T4 BLE Clock Project adds a way to set a DS3231 real-time clock (RTC) from an Android phone over Bluetooth Low Energy (BLE). Connect to the clock’s advertised BLE device, T4_Set_Time, and the app sends the phone’s current system time to the RTC. It is intended for occasional time correction, not as a continuously connected time source. The project page describes it as an enhancement to an earlier TTGO T4 clock. Hackster.io project page
What the TTGO T4 BLE Clock does
The clock combines a LILYGO TTGO T4 board, a DS3231 RTC, and a display. The BLE addition lets an Android phone set the DS3231 from the phone’s current system time when correction is needed. The Hackster project page, published October 19, 2024, lists one TTGO T4 and one DS3231 RTC; it says no additional hardware is needed for the BLE enhancement beyond the original clock project, apart from installing the Android app. The full parts list for the earlier clock is not established on that page, so these are not necessarily all the parts required to reproduce the complete clock. Hackster.io project page
What you need to recreate the documented enhancement
- A LILYGO TTGO T4 ESP32 development board.
- A DS3231 RTC module connected through the board’s I2C port.
- The clock sketch and its required Arduino libraries, including TFT_eSPI, the DS3231 library, and ESP32 BLE classes, as used by the project.
- An Android phone with the project’s app installed. The project page describes the app’s function but does not establish a current download location or compatibility list; verify availability and compatibility before relying on a particular app source.
LILYGO lists the T4 V1.3 as an ESP32 board with 4 MB flash, 8 MB PSRAM, Wi-Fi 802.11 b/g/n, Bluetooth 4.2+BLE, and a 320×240 ILI9341 display. These are manufacturer specifications for that listed revision, not a guarantee that every T4 variant has identical configuration. Check the board revision and pinout against the build instructions before wiring or compiling. LILYGO T4 product listing
How phone-to-clock time setting works
- At startup, the sketch initializes the display, I2C communication, DS3231 library, and ESP32 BLE components.
- The ESP32 creates a BLE server and advertises the device name
T4_Set_Time, along with a service and a readable/writable characteristic. - The Android app connects to that BLE device and sends time data based on the phone’s current system time.
- The sketch parses the received data and uses it to set the DS3231 RTC.
The code waits up to 30 seconds for a BLE connection during startup. If time setting does not complete, it proceeds to display mode. That makes the phone connection a startup correction step; the project description does not establish that the clock continuously tracks the phone or synchronizes over a network. The page’s exact description is: “The original TTGO T4 Clock project but enhanced to set the DS3231 RTC over Bluetooth (BLE).” Hackster.io project page
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Configure TFT_eSPI for the exact T4 revision
The project uses TFT_eSPI for the screen and explicitly says its setup must match the particular TTGO T4 model. Before treating a blank, miscolored, or otherwise incorrect display as a wiring or RTC fault, check the library’s configuration files:
User_Setup.hUser_Setup_Select.h
Set the display driver and pin configuration to match the board revision and project wiring. LILYGO’s product listing identifies an ILI9341 320×240 screen for its T4 V1.3 listing, but that specification alone does not supply the project’s exact pin mapping. Use the project’s configuration and your board’s revision-specific details rather than assuming another T4 setup is interchangeable. Hackster.io project page LILYGO T4 product listing
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What this project does—and does not—establish
The described benefit is convenient occasional correction: the RTC can be set from the Android phone instead of requiring the user to set it directly. The project page does not report measured clock accuracy, battery life, current draw, or a tested range for BLE connection, so those results should not be inferred from the design description.
Espressif’s general ESP32 BLE guidance specifies that Bluetooth LE sleep-clock accuracy must be within 500 PPM. It also explains that using the main crystal for BLE low-power operation keeps that crystal powered during light sleep and raises current consumption; average current varies with the application, BLE configuration, and time spent transmitting or receiving. This is platform guidance, not a measurement of this clock, and it does not establish the clock’s battery life. Espressif ESP-IDF BLE low-power documentation
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Keep the project separate from LILYGO’s T4 demo
LILYGO also maintains a TTGO-T4-DEMO repository, but it is a separate cryptocurrency ticker project using Wi-Fi and an ILI9341 screen—not this BLE clock. Do not treat that repository as the source for the clock’s BLE time-setting flow. LILYGO TTGO-T4-DEMO repository
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