Bluetooth Pressure Transducer

The purpose of this project is to create Bluetooth Pressure Transducer that can be connected to pressure profiling apps (SE Profiler, Coffee Flow & Odyssey Espresso).

The target espresso machine was my Flair 58. This espresso maker has a G1/8 fitting for the pressure gauge.

Diagram

Following diagram depict the configuration of the current implementation.

flowchart BT
    A(Analog Pressure\nTransmitter) <-->|wired| B(ESP32 Dev Board)
    B<.->|BLE/Bluetooth|C(Android/iPhone\nSE Profiler, Coffee Flow, Odyssey Espresso Apps)

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Bill of Material

This device consist of following components:

• ESP32 Dev board (WEMOS LOLIN32 OLED)
• Breadboard
• Analog Pressure Transmitter 5V DC

ESP32 Dev board (WEMOS LOLIN32 OLED)

I'm using this board because there is OLED embedded in the board so we just need the programming part without having trouble to do wiring on display component.

The display component will be used to display the current status of the device. Whether connected to the app or not. Also to display current pressure reading by the analog pin.

Analog Pressure Transmitter 5V DC

WARNING: Make sure youre using high temperature version of the sensors before using it with your espresso machine

The analog pressure transmitter wiring will have :

• 5V (power)
• Ground
• Output

@frontmesh has provided some information regarding two types of G1/8 fittings, short and long. I'm guessing Flair 58 is using the lengthy version. It would be preferable if you could have this long-fitting version — and please share it with us.

Wiring

From above schematic, we will need to connect Pressure Transmitter to 5V, GND and some analog PIN (I choose ADC19/GPIO26).

Code Part

At the moment I will put only the binary to this repository. However the snippet for pressure calculation is availbale in the repository.

Flashing Firmware using ESPTOOL

Download the binary provided in the release section. The binary will consists of following files:

1. BluetoothPressureTransducer_InternalLCD.ino.bootloader.bin
2. BluetoothPressureTransducer_InternalLCD.ino.partitions.bin
3. BluetoothPressureTransducer_InternalLCD.ino.bin
4. boot_app0.bin (this files should be provided by ESPTOOL during package installation - make sure your environment already have running Arduino IDE with ESP32 pack)

Run following command (some parts will need you to adjust to match your own environment):

{PATH_TO_ESPTOOL}/esptool --chip esp32 --port "{CHANGE_TO_YOUR_DEVICE_PORT}" --baud 115200  --before default_reset --after hard_reset write_flash  -z --flash_mode dio --flash_freq 80m --flash_size 4MB 0x1000 BluetoothPressureTransducer_InternalLCD.ino.bootloader.bin 0x8000 BluetoothPressureTransducer_InternalLCD.ino.partitions.bin 0xe000 "{PATH_TO_YOUR_ESP32_PACKAGE}/packages/esp32/hardware/esp32/2.0.7/tools/partitions/boot_app0.bin" 0x10000 BluetoothPressureTransducer_InternalLCD.ino.bin

For your reference, in my environment (OSX) will need to run using following parameters:

"/Users/sybond/Library/Arduino15/packages/esp32/tools/esptool_py/4.5.1/esptool" --chip esp32 --port "/dev/cu.usbserial-0001" --baud 115200  --before default_reset --after hard_reset write_flash  -z --flash_mode dio --flash_freq 80m --flash_size 4MB 0x1000 "/private/var/folders/pz/jkl6w3fs45v88wcck8qtfhw00000gn/T/arduino/sketches/4E4A8C476EDC2D7C933461960E7BD641/BluetoothPressureTransducer_InternalLCD.ino.bootloader.bin" 0x8000 "/private/var/folders/pz/jkl6w3fs45v88wcck8qtfhw00000gn/T/arduino/sketches/4E4A8C476EDC2D7C933461960E7BD641/BluetoothPressureTransducer_InternalLCD.ino.partitions.bin" 0xe000 "/Users/sybond/Library/Arduino15/packages/esp32/hardware/esp32/2.0.7/tools/partitions/boot_app0.bin" 0x10000 "/private/var/folders/pz/jkl6w3fs45v88wcck8qtfhw00000gn/T/arduino/sketches/4E4A8C476EDC2D7C933461960E7BD641/BluetoothPressureTransducer_InternalLCD.ino.bin"

Currently I have 2 versions of firmware:

1. For 0-200psi pressure transmitter (discontinued)
2. For 0-1,6MPa pressure transmitter (I recently purchase from here; make sure to put note about G1/8 fitting)

Config Characteristic

Latest version of the firmware, now support of write Config Characteristic (873ae82d-4c5a-4342-b539-9d900bf7ebd0). The purpose of this characteristic is to able customized sensor reading based on the manual calibration. The characteristic expecting following data:

Config parameter	Format	Sample
minADC	00 {4 bytes int}	00 c7 01 00 00 = set minVoltage to 455
maxADC	01 {4 bytes int}	01 34 0d 00 00 = set maxADC to 3380
maxMilibar	02 {8 bytes long}	02 80 3e 00 00 00 00 00 00 = set maxMilibar to 16000

The parameters will be involved into following calculation to determine pressure value:

pressure in milibar = (analogReading - minADC) * (maxMilibar) / (maxADC - minADC);

Following is the default parameters value:

1. Minimum ADC (minADC default value is 455)
2. Maximum ADC (maxADC default value is 3380)
3. Maximum milibar (maxMilibar default value is 9000)

The default value is the working parameter for current pressure sensor I use (0.5V-4,5V, 0-1,6Mpa).

Serial Config Interface

Other option starting from v3.0, you can configure the parameters via serial interface.

1. Just connect to the ESP32 Bluetooth using Serial Bluetooth Terminal (Android) or another similiar apps.
2. Type info. The syntax structure should be self explaining from this point.