The device is based on the version without the music chip - in this version, the MCU has enough free pins to connect additional segments and an NMEA device.
Additional segments are connected to pins 21 (P3.6) and 22 (P3.7) of the MCU.
The S2 button was originally connected to pin 15 (P.3), but I had to connect to the pin 7 (P1.4) instead. The reason for this was that I wanted to receive data from an NMEA device on pin 15 (P3.0). This mapping occurs when the constant MAP_SW2_TO_P1_4 is defined.
If you are not planning to synchronize time via NTP or GPS, then the S2 button can be connected to pin 15.
I wanted the NMEA device to be on only during the synchronization process. To achieve this, I added a transistor switch (Q7 on the circuit) connected to pin 6 (P1.3). There is also an LED (D1) indicating that the NMEA device is on.
The rest of the schematic is as original.
The main board is extended with a piece of a prototyping board on which additional segments, transistors and buttons are mounted.
More photos here
Note: The firmware is fully backward compatible with the original 4-digit version.
The firmware is updated to display seconds on additional segments. To the enable the 6 digit support it must be built with the SIX_DIGITS constant defined. Almost all screens were updated to take advantage of the additional segments.
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Main
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Temperature
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Date
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Alarm
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NMEA settings
- Timezone (1 h)
- Timezone (-12 h)
- DST (daylight saving time) is ON
- DST (daylight saving time) is OFF
- Automatic time synchronization is set to 3 hours
- Automatic time synchronization is OFF
- Timezone (1 h)
The operation flow is shown on the following diagram:
Time can be synchronized with an NMEA device - either a GPS receiver or a microcontroller using the NTP protocol. For the second option, you need to use an ESP8266 Wi-Fi module.
I consider the first version of the clock as experimental, so I decided to place an NMEA receiver together with the transistor switch on a separate prototyping board which is attached to the main board. In this way I gave myself the opportunity to experiment, in a stable version it could be done better and more compactly.
More detailed information can be found in the GPS synchronization section.
More detailed information can be found in the NTP synchronization section.
The case is made from 3mm thick clear acrylic using laser cutting. It consist of 7 parts, designed in Inkscape, the design can be found here. The parts are glued together to form the front and back sides, which are connected with 2mm screws and spacers.
