Humidity Sensors for Homekit / Home Assistant

This project is giving the opportunity to create energy efficient sensors with a long battery life. In addition you have the convenient features of tracking the battery level and charging the battery directly with the charge usb-c port. So once your build is finished you optimally never have to open the case again. Additionally you can numerate your sensors, so you can give the case the same number as the Homekit instance.

Credits:

I based my 3d model and my hardware build on the Youtube video from Ravi Singh. Also the code I linked at the components part is from him. If you want to use more then one sensor you have to make a few minor changes in the code. I recommend using different HomeSpan Channels for the different sensors, because otherwise it can come to connection errors. Also i changed the sleep time to 15min and used the Battery Sense library for a more accurate state of charge measurement. There you can also find more detailed information about how the voltage divider works.

Components:

The hyperlinks are the products i used to build my sensors and hub with. Use them for size references.

Hub (around 3,5€):

• 1x Esp32-C3 Super Mini Board

• 4x M3 threaded inserts (hole length 5.7mm and width 4mm)

• 4x M3 Screws (max. 8mm)

• Code

Sensor (around 16€):

• 1x Esp32-C3 Super Mini Board

• 1x 1/4 sized solderable Breadboard 

• 8x M3 threaded inserts (hole length 5.7mm and width 4mm)

• 8x M3 Screws (max. 8mm)

• 1x NDP6020P TO-220 PMOS or similar

• (1x DC DC Step Up board)

• 1x TP4056 battery control module

• 1x 1000mAh Li-Po Battery

• 1x AHT10 sensor module

• 2x 2kΩ resistor

• 2x 1kΩ resistor

• 1x PN2222 npn transistor or similar

• Code

+ additional cables and connectors. I used JST-XH 2.54mm connectors for the battery

Gear:

To successfully build the project you need a soldering iron, a screwdriver and a crimping tool. For a convenient and healthier soldering experience I can recommend my soldering fume extraction.

Building:

The following description is for the sensors. For the hub no soldering is needed.

Voltage Divider Board (VDB):

This is the most complex boards because it had to be fully self soldered. In the following table the pins are described as in the picture of the red sensor:

Battery Control Board:

Here the B+/B- pins are attached to the voltage divider board. The Out+/Out- pins are connected to the DC DC Step Up Board or directly to the 5V and gnd pins of the esp32-c2 super mini board.

AHT10:

DC DC Step Up Board:

The Input comes from the battery control board. Also you have to remove the connections of A and B so the voltage is regulated to 5V. I also recommend to remove the connection next to the blue led, because it is really bright and not important to check the function because the esp board has its own led. The output can be connected to the 5V and GND pins of the esp board.

ESP32-C3 Super Mini:

Out of the other soldering description you can connect the wires to the esp pins. For programming the esp32-c3 you have to hold the boot button and press reset. This is important for first programming and for programming when the esp is in deep sleep.

Additional Info:

I also build some boards without the dc dc step up module and it works when the battery is fully charged, but i did't test it with a lower battery. It could create connection errors when voltage is too low. Theoretically you can reduce the price, when you only use an esp32-c3 with a Li-Po battery and an aht10 sensor.