This instructable will show how to make a Bluetooth Low Energy Internet of Things device to monitor the Electrical Conductivity of a hydroponic nutrient solution.

The hardware will be any ESP32 development board and a uFire Isolated EC Probe Interface.

We will display our data on a simple webpage that connects to our device through Web Bluetooth.

Step 1: Things You'll Need

Any ESP32 development board. This one seems reasonable, but any will work.
An Isolated EC Probe Interface board and a K1 conductivity probe. You can get them both at ufire.co
Some odds and ends like wires and USB cables.

Step 2: Connections

The ESP32 we are using has WiFi and BLE interfaces, so that just needs a power supply. You'll probably want a USB cable supplying mains power, but a battery is another option. Many ESP32s can be bought with battery charging circuitry already on the board.

The uFire device that we will be measuring EC and temperature connect to the ESP32 by the I2C bus. With the ESP32, you can choose any two pins for I2C. Both devices will be on the same bus, so the SCL and SDA pins will be the same. If you look at the code, you will see this line.

uFire_EC_BLE ec_ble(19, 23);

I decided to use pin 19 for SDA and pin 23 for SCL. So Connect the ESP32's 3.3v (or whatever the pin may be called on your particular board) to the EC uFire device's 3.3/5v pin, GND to GND, 19 to SDA, and 23 to SCL. Now connect the uFire pH board to the EC board, pin for pin. Your ESP32 board may have a different pin-out than the picture.

Step 3: The Software

I will assume you are familiar with Arduino, the Arduino IDE, and have it installed already. If not, follow the links.
Next thing is getting the ESP32 platform installed. For some reason, this hasn't been simplified by the available platform management features the IDE has to offer, so you'll need to go to the github page and follow the appropriate installation instructions.
Now for the libraries:
1. From in the Arduino IDE, goto Sketch / Include Library / Manage Libraries... and search for and install 'Isolated EC Probe Interface'.
2. Search for and install 'ESP32 BLE Arduino'

Step 4: The Sketch

The sketch for this project is quick and easy.

You can find it on the github page. It will also be in the BLE example. And for good measure, it's attached to this instructable as well.

#include "uFire_EC_BLE.h"<br>
// On the ESP32, the I2C pins can be chosen. In this case, sda=19 and scl=23 
uFire_EC_BLE ec_ble(19, 23);

void setup() {
  // start the BLE server
  ec_ble.startBLE();
}
void loop() {
  // loop through and take continous measurements
  ec_ble.measureEC();
  ec_ble.measureTemp(); 
}

BLE.ino
Download

Step 5: Displaying Our Data

Now that the hardware is setup, we need a convenient way to display our data. For that, we will make a simple webpage that uses Web Bluetooth. If you aren't familiar with it, it's a Javascript API that is currently only available on Chrome. It allows you to connect to a BLE device from a webpage.

Have a look at the github repo.

As a quick overview:

it uses bulma.io for styling
Vue for front-end framework
app.js contains all the javascript code
index.html contains all the html

Some things to keep in mind, if you want to develop your own webpage:

it needs to be served from an https server, you can't access it from a local file (file://). Here is a good python https webserver to get started.
Only Chrome version 55+ works for this particular implementation. You could write an app or program using the more traditional BLE APIs.
Make sure Experimental Web Platform features is Enabled by going to chrome://flags/#enable-experimental-web-platform-features and restarting the browser. On newer versions of Chrome, this is enabled by default.

Step 6: Using the Webpage

Now that everything is put together, programmed, and the website is being served, we can look at the end result.

Open the website, in our case, it lives at https://ufire.co/uFire_BLE/, click the Bluetooth icon in the upper right and choose the uFire EC device. Now you should be seeing the EC reading in mS and the temperature in C.

You can also set some calibration options.