ESP32 flipdot clock

An ESP32 clock using GPS or WiFi for the time source. It also integrates the SCD30 CO2, humidity, and temperature sensor. It will display the time on a flipdot display.

Building

Build using Arduino IDE for the WEMOS Lolin32 OLED board. Dependencies (libraries):

• Sensirion I2C Scd30
• Adafruit GFX
• Adafruit SSD1306

Pinout

The pinout for the peripherals is defined in the config.hpp file.

Feature details

Time Source

GPS

If a GPS fix is acquired, the clock uses GPS time as the time source.

NTP

If the clock is connected to a WiFi network, it uses NTP time to get the UTC time.

Localtime

If GPS or NTP time has been acquired once, but it is no longer available, then the clock uses the ESP32's local time as the time source. This might drift over time.

Priority

The time sources are used in the following priority:

1. NTP
2. GPS
3. Localtime

Time zone

The time zone is defined in config.hpp. The clock ignores the NTP time zone.

WiFi configuration

The default WiFi password and SSID can be configured in config.hpp. The WiFi SSID and password can be changed over serial by typing config, followed by the new SSID and password. If the new connection is successful, the new SSID and password will be saved to the ESP32's flash storage.

Flipdot Matrix

Each flipdot pixel is connected to two flipdot controllers. The contorollers pass current through a coil, which puts the pixel into the correct orientation. Because of this, the X and Y controllers have to specify opposite voltage levels, so that current can flow through the coil.

Each flipdot controller is addressed via a shift register. The input to the shift register and flipdot controller is inverted.

            ┌────────┐     ┌────────┐    ┌──────────┐ 
            │Inverter│     │Shift   │    │Flipdot   │ 
            │        │     │Register│    │Controller│ 
 ~Data ────>│    Data│────>│IN      │    │Rows/Cols │ 
 ~CLK  ────>│    CLK │────>│CLK     │    │(FP2800A) │ 
 ~LOAD ────>│    LOAD│────>│LATCH   │───>│ADDR      │ 
 ~EN   ────>│    EN  │──┐  │        │  ┌>│EN        │ 
            └────────┘  │  └────────┘  │ └──────────┘ 
                        │              │              
                        └──────────────┘              

The flipdot matrix is controlled by shifting in two 8-bit words into shift registers. The word specifies the X (or Y) address and voltage level for the controller (HIGH/DRAIN). The word format is the following:

 ┌───────────────────┐                                                
 │ MSB       LSB     │     Sent MSB First                             
 │  V         V      │                                                
 │ ┌─┬─┬─┬─────┐     │    ┌──────────────┐           ┌──────────────┐ 
 └─│\│D│\│ADDR │     └──> │Shift Register│ ────────> │Shift Register│ 
   └─┴─┴─┴─────┘          └──────────────┘           └──────────────┘ 
    ∧ ∧ ∧   ∧               X Coordinates              Y Coordinates  
    │ │ │   │                                                         
    │ │ │   └─── 5 bit|row/column address                             
    │ │ └─────── 1 bit|unused                                         
    │ └───────── 1 bit|Data high/low                                  
    └─────────── 1 bit|unused                                         

After the X and Y data is loaded into the shift registers and latched, pulling the EN pin low will enable the flipdot controllers and flip a single pixel.

Note

the X and Y coordinate addresses might not be in order on some flipdot displays. Check this if your lines/columns are out of order. The mapping for the flipdot display can be found in flipdot_interface.cpp under x_to_fp_addr() and y_to_fp_addr().

SCD30 CO2 Sensor

The project uses the Sensirion SCD30 CO2 sensor to take CO2, Temperature and Humidity readings. It communicates over I2C and uses the Sensirion library.

Photodiode

The photodiode is wired up through a comparator, where HIGH (~2.5V) indicates low light, and LOW (~0V) indicates enough light. This is used to save power and cycle counts on mechanical elements when the clock is too dark to read.

OLED Display

Basic status information is displayed on the ESP32 dev board's built-in oled display. If no display is present, this feature will be ignored. Pins can be configured through config.hpp