In the process of expanding the family of supported displays for the WiFiChron clock, I found this amazing VFD module on aliexpress:

It has an SPI interface, it is powered by 5V, character set is defined and stored internally.

A quick search produced a sketch and documentation for the driver, PT6302.

According to the PCB silkscreen, the VFD module is powered by 5V, but the signals are 3V3. (The 30V required by the VFD glass itself is made by the on-board switching mode power supply, so no need to worry about generating high voltage externally.) An ESP32 board would be the perfect candidate to control this display. Luckily, the found sketch was also written for ESP32, so all I had to do was compile and upload using Arduino IDE 1.8.13. The only problem was that my IDE installation did not show ESP32 boards anymore, even though I used it once previously. Therefore, I had to re-visit the whole setup process once again. This time I am documenting it, to save on any future effort. So here are the steps:

• install Arduino IDE (1.8.13, in my case) from Windows store, placed here:

#include <WiFi.h>
#include <WiFiUdp.h>
#include <NTPClient.h>
#include <TimeLib.h>

WiFiUDP ntpUDP;
NTPClient timeClient(ntpUDP, "cn.ntp.org.cn", 8*3600, 60000);
const char *ssid     = "<wifinet>";
const char *password = "<password>";

uint8_t din   = 33; // DA
uint8_t clk   = 12; //23; // CK
uint8_t cs    = 13; //19; // CS
uint8_t Reset = 27; //22; // RS

char *str_time = "00:00:00";
String format_time = "00:00:00";

void write_6302(unsigned char w_data)
{
  unsigned char i;
  for (i = 0; i < 8; i++)
  {
    digitalWrite(clk, LOW);
    if ( (w_data & 0x01) == 0x01)
    {
      digitalWrite(din, HIGH);
    }
    else
    {
      digitalWrite(din, LOW);
    }
    w_data >>= 1;
    digitalWrite(clk, HIGH);
  }
}

void VFD_cmd(unsigned char command)
{
  digitalWrite(cs, LOW);
  write_6302(command);
  digitalWrite(cs, HIGH);
  delayMicroseconds(5);
}

void S1201_show(void)
{
  digitalWrite(cs, LOW);
  write_6302(0xe8);
  digitalWrite(cs, HIGH);
}

void VFD_init()
{
  // set number of characters for display;
  digitalWrite(cs, LOW);
  write_6302(0xe0);
  delayMicroseconds(5);
  write_6302(0x07);  // 8 chars;
  digitalWrite(cs, HIGH);
  delayMicroseconds(5);

  // set brightness;
  digitalWrite(cs, LOW);
  write_6302(0xe4);
  delayMicroseconds(5);
  write_6302(0x33); // level 255 (max);
  digitalWrite(cs, HIGH);
  delayMicroseconds(5);
}

void S1201_WriteOneChar(unsigned char x, unsigned char chr)
{
  digitalWrite(cs, LOW);
  write_6302(0x20 + x);
  write_6302(chr + 0x30);
  digitalWrite(cs, HIGH);
  S1201_show();
}

void S1201_WriteStr(unsigned char x, char *str)
{
  digitalWrite(cs, LOW);
  write_6302(0x20 + x);
  while (*str)
  {
    write_6302(*str); // ascii
    str++;
  }
  digitalWrite(cs, HIGH);
  S1201_show();
}

void setup()
{
  WiFi.begin(ssid, password);
  Serial.begin(115200);
  Serial.print("Connecting.");
  while ( WiFi.status() != WL_CONNECTED ) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("connected");
 
  timeClient.begin();

  pinMode(clk, OUTPUT);
  pinMode(din, OUTPUT);
  pinMode(cs, OUTPUT);
  pinMode(Reset, OUTPUT);
  digitalWrite(Reset, LOW);
  delayMicroseconds(5);
  digitalWrite(Reset, HIGH);
  VFD_init();
}

void loop()
{
  timeClient.update();
  format_time = timeClient.getFormattedTime();
  char *str_time = &format_time[0]; 
  S1201_WriteStr(0, str_time);
  Serial.println(timeClient.getFormattedTime());
  delay(1000);
}

In the world of 16-segment displays, Klais-16 is the biggest I have seen, at about 8cm (3") character height. Multiple displays can be daisy-chained and controlled through serial communication (1 pin, TX). It is open source and available to buy on Tindie at the very reasonable price of US$15 a piece.

The biggest challenge was mechanical, particularly, finding a way to mount the 8 individual displays. Let me explain. I received the displays as ready-to-use (assembled, programmed and tested) products. I did  not expected to dis-assemble them (not even partially) in order to mount them. The two mounting methods described in the documentation (using 15mm and 20mm profiles, respectively) ask for just that, basically to cut the original plastic rivets and, eventually, to replace them with (your own) M3 screws when fixing them to the rails. (I actually started going along with either described method until I realized I did not want to open them up). The easiest solution I found in the end was to use 1/2" x 1/2" L-profile, as shown below. For this, I only cut the middle rivets and used the holes to screw each individual display to the rails.

The software support consists in adding one class, DisplaySoftSerial.cpp, shown below.

#include <Arduino.h>
#include <SoftwareSerial.h>
#include "DisplaySoftSerial.h"

SoftwareSerial ss(7, 2);	// RX not used; TX=2;

//******************************************************************
//
void Display_t::setup()
{
  ss.begin(19200);
}

//******************************************************************
// draw the 8 characters on the screen;
//
void Display_t::writeDisplay(char* displayBuffer)
{
  char reverseBuffer[9] = {0};

  for (byte i=0; i<9; i++)
  {
    reverseBuffer[i] = (displayBuffer[7-i]);
  }
  ss.write(reverseBuffer);
}

//*******************************************************************
// brightness level is number between 0 and 7, 0 being the brightest;
//
void Display_t::setBrightness(uint8_t brightness)
{
  // cannot do;
}

//*******************************************************************
//
void Display_t::reset()
{
}

It turns out that most electronics, even prototypes, can be easily enclosed with Lego. And that means no screws, no glue, no fasteners, zero tools, just the bricks and some imagination.

This is the HDSP clock variant with 1" displays driven by HT16K33 (introduced here). The board was cut and filed (0.5mm on each side) to fit snug between the walls (see this).

Next is a HDSP clock variant with two Adafruit Quad Alphanumeric displays.

Both of the above can be mounted on a Lego wall (as found in schools) or they can desk-stand on their own.

Here is an example of a Lego-encapsulated WifiChron.

The PCB was also filed about 0.5mm on each side to fit between the lateral brick walls. It did not have to be fastened in any other way. The ESP8266 module fits inside nicely. The 3 buttons and the USB mini B connector are all easily accessible from the back.

Below is the Lego version of the Axiris clock.

And finally, a couple of OLED clocks, both running the same software on similar hardware: pro-mini + OLED shield and wsduino + 2.42" OLED shield, respectively.

Note that this is the prototype version, using a LiPo battery with charger (similar to the one shown here).

Again, all the above enclosures feel solid: nothing moves or rattles when upside down or even shaken. I did not try dropping them though :)

This post shows two WiFiChron mods, that look more like finished projects rather than just experiments.

First one uses the WiFiChron board connected on I2C to two Adafruit Quad Alphanumeric Displays (I2C addresses 0x70 and 0x71). The WiFiChron software has similar adaptation as the one for HDSP clock (see this post for details).

This (poor) video shows it in action.

The interesting thing about the Chinese clones (of the Adafruit displays) I had in hand is that each module has one (2 digit) display red and the other orange. Initially I thought it's a manufacturing error, but after checking, it seems that this is intended (for reasons I do not understand).

The second one is an "HDSP clock" with a 8-character display with 16-segment LED modules, introduced here, cased in a LEGO enclosure.

After cutting the top of board off (since there is no HDSP-2534) and a little filing of all sides, the PCB fit perfectly between the LEGO bricks.

For this display, the line that has to be enabled (un-commented) in DAL.h is:

#define DISPLAY_HT16K33

This post shows two WiFiChron mods, that look more like finished projects rather than just experiments.

First one uses the WiFiChron board connected on I2C to two Adafruit Quad Alphanumeric Displays (I2C addresses 0x70 and 0x71). The WiFiChron software has similar adaptation as the one for HDSP clock (see this post for details).

This (poor) video shows it in action.

The interesting thing about the Chinese clones (of the Adafruit displays) I had in hand is that each module has one (2 digit) display red and the other orange. Initially I thought it's a manufacturing error, but after checking, it seems that this is intended (for reasons I do not understand).

The second one is an "HDSP clock" with a 8-character display with 16-segment LED modules, introduced here, cased in a LEGO enclosure.

After cutting the top of board off (since there is no HDSP-2534) and a little filing of all sides, the PCB fit perfectly between the LEGO bricks.

For this display, the line that has to be enabled (un-commented) in DAL.h is:

#define DISPLAY_HT16K33

class Alphanum8x16 : public Adafruit_AlphaNum4
{
 public:
  void writeDigitAscii(uint8_t n, uint8_t ascii);
};

void Alphanum8x16::writeDigitAscii(uint8_t n, uint8_t a)
{
  uint16_t font = pgm_read_word(alphafonttable+a);
  displaybuffer[n] = font;

  //--------------------------------------------------------
  // this is the Adafruit mapping of digits to segments:
  // 0 DP N M L K J H G2 G1 F E D C B A
  //
  // this is the 16 seg mapping of digits to segments:
  // A2 D2 N M L K J H G2 G1 F E D1 C B A1
  //
  // bits:
  // 1  1  1 ...                 ...  1 0
  // 5  4  3
  //
  // Note: DP is not connected/controlled for the 16 seg;
  //--------------------------------------------------------

  // if A1 (bit 0) is on, set A2 (bit 15) as well;
  if (font & 1)
    displaybuffer[n] |= 0x8000;

  // if D1 (bit 3) is on, set D2 (bit 14) as well;
  if (font & 8)
    displaybuffer[n] |= 0x4000;
}