VW T4 Transporter Dash Blank Thermostat Temperature Display

A fairly simple and quick prototype of digital dash blank to fit a volkswagen T4 dashboard which reads the inside and outside temperatures in degrees C. It uses 2 Dallas temperature sensors and an ESP32 SuperMini board.

The blank is 3d Printed, this assumes you have access to a 3d printer, you could also modify an OEM switch blank, but this would be a lot of work.

Disclaimer: This is very much a prototype, information might not be 100% correct. Licence on this is open source, completely free to do as you wish with it, resell, make for yourself, modify etc.

• 0.9" OLED I2c Screen (note there are 2 sizes, you will need the "new style" 0.9" screen not the 1.3" screen)
• 2x "1 wire" Dallas DS18b20 sensors (I chose 1 with a short 1 meter wire and another with a longer 3 meter wire)
• ESP32 super mini board
• 4.7KΩ resistor
• Misc heat shrink / electrical tape / female dupont connectors

I used parts mostly off ali-express. I'm fairly certain my esp32 super mini is a clone board, finding the correct i2c pins was a bit of a headache, you might need to do some testing to find your I2C pins.

Housing

First step is to 3d print the housing / switch blank. This housing fits the new style 0.9" oled i2c screen.

I printed this with a 0.4mm nozzle, no supports, face down & a 30% infill.

Wiring

To wire up the project, I joined the earth wire from the display and dallas sensors together.

I used the 5v pin for the dallas sensors and the 3.3v pin for the display, I belive you can swap these round, or run both display and dallas sensors off the same voltage rail.

I used pin 4 for the dallas sensor 1wire input and pins 1&2 for the i2c SCK and SDA

A 4.7ohm resistor bridges the 5v rail and the yellow sensor wire, this is "normal mode" for the Dallas temperature sensor. You can run it in "parasite mode" but as we have all the wires available we'll use normal mode.

The Arduino code

The arduino code includes the onewire & dallas temperature libraries for the sensors

It also includes the Wire, adafruit gfx, and adafruit SSD1306 libraries for the oled i2c screen.

I'm not going to go into how to set up an arduino project, there are lots of tutorials but here is the code to display the van graphic and temperatures.

#include <OneWire.h>
#include <DallasTemperature.h>


#include <Wire.h>
#include <Adafruit_GFX.h>
#include <Adafruit_SSD1306.h>


#define SCREEN_WIDTH 128 // OLED display width, in pixels
#define SCREEN_HEIGHT 64 // OLED display height, in pixels


Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, -1);


// Data wire is plugged TO GPIO 4
#define ONE_WIRE_BUS 4
#define TEMPERATURE_PRECISION 9

// Setup a oneWire instance to communicate with any OneWire devices (not just Maxim/Dallas temperature ICs)
OneWire oneWire(ONE_WIRE_BUS);


// Pass our oneWire reference to Dallas Temperature. 
DallasTemperature sensors(&oneWire);


// Number of temperature devices found
int numberOfDevices;


// We'll use this variable to store a found device address
// DeviceAddress tempDeviceAddress; 
DeviceAddress inTherm, outTherm;


// 'van', 128x64px
const unsigned char epd_bitmap_van [] PROGMEM = {
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};

void setup(){
  // start serial port
  Serial.begin(9600);
  
  // Start up the library
  sensors.begin();
  
  
  // locate devices on the bus
  Serial.print("Locating devices...");
  Serial.print("Found ");
  Serial.print(sensors.getDeviceCount(), DEC);
  Serial.println(" devices.");

  if (!sensors.getAddress(inTherm, 0)) Serial.println("Unable to find address for Device 0");
  if (!sensors.getAddress(outTherm, 1)) Serial.println("Unable to find address for Device 1");

  // set the resolution to 9 bit per device
  sensors.setResolution(inTherm, TEMPERATURE_PRECISION);
  sensors.setResolution(outTherm, TEMPERATURE_PRECISION);

  Wire.begin(1,2);


  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { // Address 0x3D for 128x64
    Serial.println(F("SSD1306 allocation failed"));
    for(;;);
  }
  


}


void loop(){ 


  // Update sensors
  sensors.requestTemperatures();


  float tempCIn = sensors.getTempC(inTherm);
  int roundedTempCIn = round(tempCIn);
  String tempCstringIn = String(roundedTempCIn);
  float tempCOut = sensors.getTempC(outTherm);
  int roundedTempCOut = round(tempCOut);
  String tempCstringOut = String(roundedTempCOut);

  
  // Clear display every time
  display.clearDisplay();

  // Setup van bitmap
  display.drawBitmap(0, 0, epd_bitmap_van, 128, 64, WHITE); // possibly 1 not white


  // Set out text
  display.setTextSize(2);
  display.setTextColor(WHITE);
  display.setCursor(3, 5);
  display.println(tempCstringOut + "c");

  // set In text
  display.setTextSize(2);
  display.setTextColor(BLACK);
  display.setCursor(60, 25);
  display.println(tempCstringIn + "c");
  display.display(); 


  delay(5000);
}

You may need to swap the inside and out device address' depending on which sensor is your "long" wire for outside temperature.

If you want temperature in farenheit you can change the following:

float tempCIn = sensors.getTempC(inTherm);

to

float tempCIn = sensors.getTempF(inTherm);

For some screens you may need to change the following:

  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) { // Address 0x3D for 128x64

to

  if(!display.begin(SSD1306_SWITCHCAPVCC, 0x3D)) { // Address 0x3D for 128x64