Low cost miniature device encloses a temperature/humidity sensor in a USB stick capable of publishing to Home Assistant and ThingSpeak, without power cords.
This project encloses a temperature/humidity sensor and microcontroller in a USB stick to create a compact device capable of using WiFi to monitor the sensor using any combination of the following options:
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Computer via USB to Arduino IDE
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Home Assistant via MQTT protocol
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ThingSpeak.com, a free online IoT analytics service that provides instant visualization and analysis of live data which can send alerts.
Use this anywhere you want to monitor temerature and humidity.. your home, empty house, garage, etc. that has electrical power and internet.
If there is no internet at the place you want to monitor, consider this , which monitors via ioT cellular for less than $2 /per month for the ioT SIM card.
The microcontroller and temperature/humidity sensor fit inside a USB stick enclosure to create the device. A short cable or a USB to MicroUSB adapter provides access to USB power. Holes at each end of the enclosure allow heat to escape.
The components are available from multiple sources. Best prices are from AliExpress, but the shipping costs are a killer. Amazon has everything, but in multiple quantities. Pick your poison. Get on the Google.
USB Power source - several are available. I prefer the AILKIN because the usb socket is parallel to the wall:
5 volt power is supplied to the ESP8266 via USB connection.
Temperature/Humidity Sensor pins are connected to the esp8266 as follows:
- VCC to esp8266 3.3v
- GND to esp8266 GND
- SCL to esp8266 D1
- SDA to esp8266 D2
After the system has operation has been confirmed, solder a jumper to connect the D0 and RST pins. This will enable the processor to wake up based on the timer. New software cannot be uploaded while the jumper is connected.
The USB software is written in C++ using the Arduino IDE. You need to edit the following code to interface with Home Assistant in ThingSpeak:
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WiFi SSID and password
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Home Assistant MQTT credentials
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ThinngSpeak credentials
There are additional compile time parameters to select the option above which you want to activate. These are documented in the software.
The software operates as follows:
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On startup, the setup() procedure:
- activates the serial monitor to report each step for debug purposes (see below at the end)
- turns on the on-board LED
- initializes the sensors
- establishes communication with the publish destinations
- turns off the board LED and hands off control to the loop() procedure
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The loop() procedure:
- reads the sensors
- publishes the results
- initiates a state of deep sleep for the number of minutes in the sleepMinutes variable to minimize heat generation.
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When the processor awakens, it starts over at the setup() procedure.
As an option, this project publishes to Home Assistant (HA) via topic "device1/temperature" and "device1/humidity".
To implement it in HA, open the file editor to mqtt.yaml, and enter the following under the sensor section:
Save the file and Navigate to the Developer Tools section. Reload the "All YAML Configuration.
Open the dashboard User Interface (Lovelace in my case) to create a gauge card for temperature and another for humidity:
Create a History Graph Card with the following parameters (or not!):
Select DONE to display the result:
As an option, this project publishes to ThingSpeak.
To implement it in ThingSpeak, configure a new channnel named Device1 (or some other name) and save it.
You will need to record the Channel ID and the write API for the channel. These are the credentials you need to publish data.
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Solder connections betwwen the esp8266 and the temperature/humidity sensor but not the rst - D0 link
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Apply the applicable WIFI, MQTT, and ThinkSpeak credentials and adjust the compile time parameters accordingly
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Compile, upload and run the software
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Open the serial monitor
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Verify the serial monitor list looks like the one below, based on selections you made
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Verify the data made it to Home Assistant and ThingSpeak as expected
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Note that the device will only restart if the reset button is pushed; it will not wake up on its own yet
When everything is working as it should, solder a link to D0 and RST on the ESP8266. This enables the device to wake up repeatedly.
Let it run several wakeup cycles connected to your serial monitor. Verify all systems are as expected.
Enclose it in the enclosure and plug it in somewhere. Sit back and say "Ahhh".
The serial monitor list should be similar to the one below, based on selections you made.
There is a temperature variable and a tem variable shown. The temperature displays the most recent valid temperature. If the most recent temperature was invalid, then the tem value displays "--"; otherwise tem = temperature. The temperature variable is published. The same is true of the humidity and hum variables. This approach keeps the published history graphs in a reasonable range while at the same time providing a debug/verification mechanism.
Additional devices can be added by changing the deviceID = 1 statement in the software and the related Home Assistant and ThingSpeak software and credentials.
Setting the sleep time to 10 minutes and orienting the USB stick vertically beneath the AILKIN plug results in temperature and humidity readings which match my open air units.
Eliminating power cords and miniaturizing the packaging improves WAF (Wife Approval Factor).
Replacing those big bulky wired temperature sensors with simple USB sticks looks better and improves your chances of getting lucky more frequently.