Collecting SHT85 Sensor Data using STM32 & Bluetooth Low Energy

Overview
This is a simple Bluetooth Low Energy project showing how to get SHT85 Humidity Temperature Sensor data connected to the STM32 Nucleo-144 using javascript. We will be interfacing SHT85 Humidity& Temperature Sensor with STM32 microcontroller & collect the sensor data with BLE.
The SHT85 series is a newly designed temperature and humidity sensor from Sensations. The sensor comprises a band-gap temperature sensor to measure temperature, a capacitive humidity sensor for measuring humidity in the environment, an analog-to-digital converter, data memory, measurement data processing, and also a digital communication interface. The SHT85 operates between 2.15V to 5.5V & communicates with a microcontroller over an I2C bus.
Requirments
A BleuIO dongle (https://www.bleuio.com/)
A SHT85 sensor (https://sensirion.com/products/catalog/SHT85/)
A board with a STM32 Microcontroller with a USB port. (A Nucleo-144 development board: NUCLEO-H743ZI2, was used developing this example. (https://www.st.com/en/evaluation-tools/nucleo-h743zi.html)
To connect the dongle to the Nucleo board we used a “USB A to Micro USB B”-cable with a USB A female-to-female adapter.)
STM32CubeIDE (https://www.st.com/en/development-tools/stm32cubeide.html)
When the BleuIO Dongle is connected to the Nucleo board’s USB port, the STM32 will recognize it and start advertising the sensor values that it reads from the SHT85 along with the sensor serial number. It will update these values every 10 seconds.
Setup the project
Setup the project
Get project here:
https://github.com/smart-sensor-devices-ab/stm32_bleuio_SHT85_example
Either clone the project or download it as a zip file and unzip it, into your STM32CubeIDE workspace.
Importing as an Existing Project
From STM32CubeIDE choose File>Import…
Then choose
General > Existing Projects
into Workspace then click ‘
Next
>’
Make sure you’ve chosen your workspace in ‘
Select root directory:
’. You should see the project “stm32_bleuio_SHT85_example”, check it, and click ‘Finish’.
If you download the project as a zip file you will need to rename the project folder from ‘
stm32_bleuio_SHT85_example-master
’ to ‘
stm32_bleuio_SHT85_example
’
Connect the SHT85 Sensor SDA to PF0 on the STM32 Nucleo board and SCL to PF1. Then setup I2C2 in the STM32Cube ioc file like this:
Running the Example
In STMCubeIDE click the hammer icon to build the project.
Open up the ‘STMicroelectronics STLink Viritual COM Port’ with a serial terminal emulation program like TeraTerm, Putty or CoolTerm.
Baudrate: 115200
Data Bits: 8
Parity: None
Stop Bits: 1
Flow Control: None
In STMCubeIDE click the green play button to flash and run it on your board. The first time you click it the ‘Run Configuration’ window will appear. You can just leave it as is and click run.
Connect the BleuIO Dongle.
Access SHT85 sensor data from a web browser
We wrote a simple script that connects to the BleuIO dongle and reads advertised data from STM32.
For this script to work, we need
BleuIO USB dongle
connected to the computer.
BleuIO javascript library
Chrome 78 or later, and you need to enable the
#enable-experimental-web-platform-features
flag in
chrome://flags
A web bundler – (
parcel js
)
Steps
Create a simple Html file called index.html which will serve as the frontend of the script. This Html file contains some buttons that help connect and read advertised data from the remote dongle, which is connected to stm32.

<
!
DOCTYPE
html
>
<
html
lang
=
"en"
>
<
head
>
<
!
--
Required
meta
tags
--
>
<
meta
charset
=
"utf-8"
/
>
<
meta
=
"viewport"
content
=
"width=device-width, initial-scale=1"
/
>
<
!
--
Bootstrap
CSS
--
>
<
link
href
=
"https://cdn.jsdelivr.net/npm/
[email protected]
/dist/css/bootstrap.min.css"
rel
=
"stylesheet"
integrity
=
"sha384-1BmE4kWBq78iYhFldvKuhfTAU6auU8tT94WrHftjDbrCEXSU1oBoqyl2QvZ6jIW3"
crossorigin
=
"anonymous"
/
>
<
title
>
STM32
Read
sensor
value
<
/
title
>
<
/
head
>
<
body
>
<
div
class
=
"container mt-5"
>
<
h1
>
Sensor
data
collection
from
stm32
using
Bluetooth
Low
Energy
<
/
h1
>
<
button
id
=
"connect"
class
=
"btn btn-primary"
>
Connect
<
/
button
>
<
button
id
=
"getdata"
class
=
"btn btn-success"
>
Get
device
data
<
/
button
>
<
div
id
=
"loader"
>
<
/
div
>
<
br
/
>
<
div
id
=
"response"
class
=
"fw-bold"
>
<
/
div
>
<script
src
=
"./index.js"
>
</script>
<
/
div
>
<
/
body
>
<
/
html
>
Create a js file called script.js and include it at the bottom of the Html file. This js file uses the BleuIO js library to write AT commands and communicate with the other dongle.

import *
as
my_dongle
from
'bleuio'
//connect to BleuIO
document
getElementById
(
'connect'
)
addEventListener
(
'click'
function
(
)
{
my_dongle
at_connect
(
)
}
)
//get sensor data
document
getElementById
(
'getdata'
)
addEventListener
(
'click'
function
(
)
{
document
getElementById
(
'loader'
)
innerHTML
=
'Loading'
//set the BleuIO dongle into dual role
my_dongle
at_dual
(
)
then
(
(
)
=
>
{
// sensor id of the device that we are trying to get data from
let
sensorID
=
'05084FA3'
//look for advertised data of with the sensor id
my_dongle
at_findscandata
(
sensorID

)
then
(
=
>
{
//split the advertised data from the respnse
let
advdata
=
[
length

]
split
(
" "
)
pop
(
)
//trim the advertised string to only get sensor response
const
result
=
advdata
split
(
sensorID
)
slice
(

)
join
(
sensorID
)
//get temperature and humidity value
let
temp
=
result
substring
(

)
;
let
hum
=
result
substring
(

)
;
//convert from hex to decimal and device by 100
temp
=
parseInt
(
temp

)
/

hum
=
(
parseInt
(
hum

)
/

)
toFixed
(

)
document
getElementById
(
'loader'
)
innerHTML
=
''
document
getElementById
(
'response'
)
innerHTML
=
`
Sensor
ID
:
05084FA3
<
br
/
>
Temperature
:
$
{
temp
}
°
C
<
br
/
>
Humidity
:
$
{
hum
}
%
rH
<
br
/
>
`
}
)
}
)
}
)
The script js file has two button actions; connect and read advertised data.
We also need to update the Sensor ID on line 13 of script js. The Sensor ID of this example project is 05084FA3, which we got from SHT85.
Therefore this script looks for advertised data that contains sensor ID 05084FA3. After getting advertised data, we split the temperature and humidity information and show it on our index.html page.
Now we need a web bundler. We can use
parcel.js
Once parcel js is installed, let’s go to the root directory and type
“parcel index.html”
. This will start our development environment.
Let’s open the script on a browser and select the right port where the dongle is connected.
This is how you can collect SHT85 Humidity Temperature Sensor Data with STM32 & Bluetooth Low Energy. The web script is available on the web script folder of the GitHub repository.