I'm always on the look out for interesting displays which can be used for clocks and was happy to find a Futaba 7-bt-317nk on aliexpress recently which appears to come from a surplus lot originally intended for video recorders on similar home entertainment devices.
It is a modified version of the standard 16 segment "starburst" pattern but with an additional 5 segments.
It has the unusual feature of including an indicator to signal that WiFi is available and a clock dial symbol which I have used to indicate that a recent time synchronisation has occurred. The hardware design was partly inspired by Sprites mods - Simple VFD-controller - A whatnow? particularly the creative use of an ancient series CD4094 shift registers which can handle the 15 volts or so required to drive the display. The filament voltage (I'm using 2.7v) is provided from 5v dropped by three silicon diodes in series. The MCU is an ESP32-C3 Supermini which is soldered directly to the PCB (no filled copper zones under the antenna). The 15volts is derived from an SX1308 boost converter module (best set to the correct output voltage before soldering it to the PCB).
The software uses basic ESP32 native SNTP clock code (credits in the program). I plan later to use a better featured clock design where the configuration parameters (WLAN credentials, timezone etc.) can be updated by web browser using the ESP32's AP mode.
Anyway, here is the project including pictures, code and a schematic so anyone interested can duplicate it or use it as the basis of their own design.
Thanks for that and I've corrected the spelling but will leave the filenames as original.
The phototransistor will be used in a future release of the software which is more or less ready but I'm waiting for the ESP32 Arduino 3.x core to be released (>Beta) before I base any published projects on my enhanced code base (which includes other features like, for example, supplying the configuration parameters via a web browser (AP mode). That core release should handle the NTP and UNIX rollovers in 2036 and 2038 reliably. Actually the code for the Futaba VFD clock is more or less 90% driver for the display and the clock code was intended to be minimal so as not to obscure the display driver logic too much. For using the photo transistor to dim the display I'll have two options. One is to use PWM to control the OE (output enable) pin of the shift registers where the duty cycle will be dependent on the ambient light. The other is to shorten the "ON" period in the multiplexing cycle dependent again on the ambient light. Anyway. I've been quite productive today and have built another one since I had the parts!
Great, thanks for clarifying, and I really like the auto-dimming concept. I never thought about the 2036/38 rollover; I have a few NTP-enabled projects running here at home, but never thought about their lifetime beyond a handful of years. Thanks for the heads up!