What is it?

This is an appallingly small (15 mm x 18 mm) pc board intended to be mounted onto a 9 V battery that will stream data to your local network so environmental conditions at any remote location around the house can be monitored wirelessly in your web browser. The device uses the ESP8285 Tensilica 80 MHz MCU with 1 MByte embedded flash and comes with a BME280 combination temperature, pressure and humidity sensor and a VEML6040 RGBW ambient light sensor.

The board has a MIC5219 3V3, 500 mA (peak) LDO voltage regulator that accepts input from 2.5 to 12 V to allow powering by a standard 9 V battery, although three AA batteries or a LiPo battery can also be used. The intent is to mount the board directly onto the 9 V battery to form a small and convenient package for placing just about anywhere. I put them above thresholds indoors to monitor conditions in a room, or above the patio door to monitor conditions outside. But this device can be placed wherever you can place a 9 V battery!

With light sleep mode enabled the average current consumption drops from ~20 mA with modem sleep (default) to around 10 mA at a five second wifi broadcast period. This is small enough that the device can continuously broadcast for about two days (~40 hours) on a 9 V battery. The current draw is large enough that the temperature reading of the BME680 will typically be a few degrees above the actual ambient air temperature. It helps to have the device mounted onto a 9 V battery with foam tape and a magnetic strip (just ask if you want these for your board) since the large thermal mass of the battery can soak up some excess heat and keep non-environmental temperature variations to a minimum.

The small board breaks out GPIO pins 1 and 3 (RX/TX), pins 0 and 2 (SDA/SCL), pin 16 tied to #RST with a zero Ohm jumper for deep sleep mode, and pins 4, 5, 12, 13, 14, and 15 (pulled down by a 4K7 resistor) for general use. It is easy to add another small pcb with additional I2C sensors to expand your environmental sensing suite while keeping the small form factor and 9 V battery mounting. Use your imagination!

And while two days on a 9 V battery is not very long, the ESP8285 Environmental Sensor can take advantage of deep sleep mode in order to, for example, shut down the ESP8285 overnight while you are asleep or away at work to save more power and deliver useful data longer. The low power modes can be used to extend the life of this environmental sensor further, but I am still experimenting and developing the best strategies, and you will have to do the same for your particular application.

Testing results to date show about 24 hours when updating at 5 second intervals, and 36 hours when updating at 20 second intervals. Updates at 60 second intervals should stretch out the battery lifetime to 20 + 0.8 * 60 = 68 hours.

Of course, you could use a 5 V wall wart to power the ESP8285 Environmental Sensor but this makes it less portable and not as appallingly small as when it is mounted on a go-anywhere 9 V battery.

Why did you make it?

The ESP8285 is a wonderful device, packing a lot of processing power, enough peripherals and GPIOs to make it interesting, and, of course, embedded wifi. I have been learning how to make good use of this inexpensive but handy little device. This design allows most of the capabilities of the ESP8285 to be used to good effect. I am getting temperature, pressure, humidity, ambient light level and the RGB components of the light in microWatts per square centimeter from any location I choose streamed to my laptop and displayed on a web page. Better yet, these values are updated automatically every five seconds (or pick whatever time you choose) and I can keep track of several of these devices around the house all at the same time! It's a wonderful thing!

What makes it special?

This device is small, designed to be powered by a 9 V battery, packed with useful sensors, and can be programmed with an Arduino IDE and a 3V3 FTDI connector. All you have to do is solder on a 1-inch-long copper wire for the antenna, solder on a connector for your favorite battery, place and enjoy!

I have written a well-commented sketch that configures the sensors, sets up the wifi web server and does everything you need to get data to your local network and streamed to your laptop.

Order the pc board from OSH Park and assemble your own ESP8285 Environmental Sensor if you want to save some money or order the fully assembled and tested board from me and see how useful wireless environmental sensing can be!