This instructable is part of my DIY Home Automation series, check out main article "Planning a DIY Home Automation System". If you don't know yet what Homie is, have a look at homie-esp8266 + homie from Marvin Roger.

There are many many sensors. I'm covering the very basic ones in order to give reader the requirements to get started building "something". That might not be rocket science but that should actually work.

If you don't have the parts, watch out for my upcoming instructable "Sourcing Electronic Parts From Asia".

Let me add a few buzz words : IoT, ESP8266, Homie, DHT22, DS18B20, home automation.

Topic should be pretty clear now :-)

Step 1: Getting Started


This instructable uses D1 Mini clones. These are WiFi enabled Arduino compatible controllers using ESP8266 chip. They ship in very small form factor (~34*25mm) and are dirt cheap (~3-4$ for clones).

I'll illustrate each build using a D1 Mini, a breadboard and some sensor(s). I include a Bill Of Materials (BOM) for each but will skip obvious things like jumper wires and breadboard (mini or full). I'll focus on "active parts".

For wires/cables in diagrams (Fritzing + AdaFruitFritzing library), I used:

  • Red/Orange for power, usually 3.3V. Sometimes it will be 5V, be careful.
  • Black for ground.
  • Yellow for digital data signals : Bits are traveling and can be read as-is by chips.
  • Blue/Purple for analog data signals : No bits here, just plain voltage that must be measured and computed to understand what's going on.

Homie for ESP8266 ships a dozen examples, that's where I started to build this instructable.


The D1 is quite breadboard friendly but will save only one row of pins up and down.
Each example will have the D1 on the right side and the components on the left side. The upper and lower power rails will be used to carry either 3.3V or 5V.


Homie examples are built as ".ino" sketches for Arduino IDE. My own code is however built as ".ccp" for PlatformIO.

This will make very little difference as sketches are simple enough to be copy/pasted whatever your tool of choice is.

Step 2: Temperature & Humidity : DHT22 / DHT11

Building the device

The DHT22 uses :

  • One digital pin to communicate with the controller, connect it to D3
  • Two wires for power (3.3V or 5V + GND)
  • The digital pin must be kept high (connected to power), for this we use a resistor between power rail and data pin


The PlatformIO project can be downloaded from : https://github.com/amayii0/Homie-DHT22

The original Homie example is here (but does not use a sensor) : https://github.com/marvinroger/homie-esp8266/blob/...

For DHT22, use DHT sensor library (ID=19)


  • Controller : Wemos D1 Mini
  • Resistor : 10KΩ
  • Sensor : (one of these)
    • DHT22 : I've used the 4 pins kind which requires an extra resistor. There are 3 pins modules shipping as SMD which includes the resistor.
    • DHT11 : This is cheaper but less accurate, check your requirements

Step 3: Waterproof Temperature : DS18B20

Building the device
The DS18B20 uses :

  • One digital pin to communicate with the controller, connect it to D3
  • Two wires for power (3.3V or 5V + GND)
  • The digital pin must be kept high (connected to power), for this we use a resistor between power rail and data pin

The DS18B20 is a 1-wire sensor. It uses a bus and as such multiple sensors can use a single data pin.

It is also possible to NOT use 3.3V/5V to power the sensor, this is called parasitic power mode. See datasheet for details.


The PlatformIO project can be downloaded from : https://github.com/amayii0/Homie-DS18B20

Like for DHT22, the original Homie example is here (but does not use a sensor) : https://github.com/marvinroger/homie-esp8266/blob...

For 1-Wire bus, use package OneWire (ID=1)

For DS18B20, use DallasTemperature (ID=54)


Step 4: Light : Photoresistor / Photocell (digital : On/off)

Building the device

(Sorry, don't have a Fritzing component for the digital photocell)

The photocell digital module uses :

  • One digital pin to communicate with the controller, connect it to D3
  • Two wires for power (3.3V + GND)

Its possible to use an analog photocell but this is not documented here, see Adafruit excellent article "Using a Photocell".

Note: In this example there's a potentiometer on the sensor board. It is used to set the limit between "light" and "dark" ambient light. When reading 1 light is off, therefor reading 0 means light if on.


The PlatformIO project can be downloaded from : https://github.com/amayii0/Homie-Photocell


Controller : Wemos D1 Mini

Sensor : Photosensitive / Light Detection Module

Step 5: Light : Photoresistor / Photocell (analog)

Building the device
The photocell analog sensor acts as a resistor. It will connect between an analog input and 3.3V.

A resistor is put between GND and data pin to create a voltage divider. The purpose is to create a known range of values:

  • If there is no light, photocell will basically block VCC, thus connecting GND to your data pin : Pin will read nearly 0.
  • It there is a lot of bright light, photocell will let VCC flow to the data pin : Pin will read nearly full voltage and as such near to max (1023).

Note : Analog pins values are read in a 0-1023 range using analogRead. This is not practical to deal with 1 byte values, for this the Arduino map function will help reduce from 0-1023 to (for instance) 0-255.

For calibration of min/max values for your sensor, use a sketch like this one from Arduino.


The PlatformIO project can be downloaded from : https://github.com/amayii0/Homie-PhotocellAnalog



Step 6: Final Words

This instructable is a very short one to explain basic monitoring.

To go further we'll need to connect relays, IR emitter... This will hopefully be covered later on as free time allows me to. The major difference is that we won't just "read" (is there light?) but also "write" (turn light on!).

<p>I used ESP8266 with 250v Relay. Unfortunately my relay board does not operate with the 3.3v Input. It needs 5v. How do you manage ?</p>
Hello,<br> Good point.<br> I still have to write that part of my instructable.<br> <br> However I've successfully used a relay board driven by a Raspberry Pi in another project.<br> The trick is that the board has 3 wires : VCC, GND and signal.<br> The VCC is directly connected to the 5V pin of the RPi while signal comes from a regular digital pin. This provides both the required voltage to operate the relay and a safe connection from the controller.<br> <br> You can find below:<br> 1/ A random module of that kind : <a href="https://www.aliexpress.com/item/1-road-relay-modules-with-optical-coupling-isolation-fully-compatible-with-3-3-V-and-5/32355065560.html" rel="nofollow">https://www.aliexpress.com/item/1-road-relay-modules-with-optical-coupling-isolation-fully-compatible-with-3-3-V-and-5/32355065560.html</a><br> 2/ My RPi setup using such board : <a href="https://github.com/amayii0/GarageOpenerR1/wiki#fritzing-schematics" rel="nofollow">https://github.com/amayii0/GarageOpenerR1/wiki#fritzing-schematics</a><br> 3/ If not using a module, this schema based on transistor should do the trick : <a href="https://electronics.stackexchange.com/a/255977" rel="nofollow">https://electronics.stackexchange.com/a/255977</a>

About This Instructable




Bio: Self taught DIYer, interested by anything electronic but without trying to launch a rocket to the moon :-)
More by RudyD1:Use Homie Firmware to Drive Sonoff Switch Module (ESP8266 Based) Building Homie Devices for IoT or Home Automation Building a Neo Geo Stick USB Adapter 
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