This nice, former railway-station clock was a so-called "Nebenuhr", triggered by a central "Hauptuhr" with 24V pulses every minute.
The wiring of the coils were initially in series for 24V usage, a quick change of the bridges made it parallel for 12V:
The motor is a Lavet-type stepping motor, needing alternating pulses. These are created by a H-Bridge (like the DRV-8833 or DRV-8871).
The program uses a straight-forward approach, with the usual suspects:
- WiFiManager
- AceCommon/AceTime for NTP & TimeZone-management
- ESP_DoubleResetDetector
After configuring the WiFi credentials by connecting to the AP nebenuhr, the time-zone and the currently displayed time on the clock must be adjusted.
If the displayed time is before the current time, the step-motor is advanced by one step and the displayed time is incremented in the memory.
If the displayed time is less than 10 minutes in the future, the step-motor is not advanced, and the clock waits until displayed- and current-time matches.
- A RC123 powered ESP-8266 D1-Mini compatible board: TTGO T-OI.
- A MT3608 DC-DC Converter
- A H-Bridge max. 10.8 V or with higher voltage limit DRV-8871
Upload the code to the ESP, connect the DC/DC-converter, adjust the output-voltage of the DC/DC-converter to the desired voltage (not exceeding the max. valtage of the H-Bridge) before connecting the H-Bridge.
After connecting the H-Bridge and the clock, connect to the nebenuhr WiFi, enter credentials, wait for reboot, connect to http://nebenuhr.local, enter the currently displayed time and time-zone, and wait for the clock to advance to the current time.
If the clock stays 1 minute off, the polarity of the motor-connection must be reversed.