Do you have a "dumb" utility meter that you want to be able to track your usage without replacing it? And do you want to run it from a battery? Then this project is for you! (If you do have a power socket nearby then other projects e.g. Home Assistant Glow are more appropriate)

Your utility meter must either have an LED that pulses for each unit consumed, or have a magnet in the dial that can be tracked with a reed switch.

IMAGE ELECTRICITY METER IMAGE GAS METER

If your utility meter has 2 rates (e.g. Economy 7 electricity meter) then make 2 of the photodiode boards and use the meter_2_rates project, otherwise use the meter_1_rate project.

You will also need an MQTT broker installed and (optionally) a Home Assistant server.

• Low-power-capable ESP32 (FireBeetle ESP32-E IoT Microcontroller)
• Dupont jumpers
• Photodiode or reed switch (depending on your meter type)
• 1 MOhm resistor (brown black green)
• Vero/strip board
• LiPo battery (1,000 - 2,000 mAh capacity should be plenty)
• USB C cable
• Blu Tack / electrical tape
• (Optional) Male header pins (if your ESP comes with soldered headers, you'll need 3 more pins)
• (Optional) USB power bank

• Soldering iron
• Sharp knife (to cut low power trace)
• Side cutters (to trim resistor/photosensor leads)
• Tiny screwdriver (to fix battery connector)
• (Optional) 3D Printer
• (Optional) Breadboard (to help solder header pins)
• (Optional) Multi-meter (to assist positioning reed switch)

If your FireBeetle comes without headers pins, then solder them on. If you do not have additional header pins, then break off a set of three pins before soldering, making sure that the missing pins are furthest away from the USB port.

The easiest way to solder is to use a breadboard to hold the pins in place while they are soldered.

Cut the "Low power" trace with a sharp knife. After doing this I measured the deep sleep current to be about 14 uA.

[IMAGE TRACE]

The photodiode or reed switch can be connected to pin A3 (for the first sensor) or pint A1 (if connecting a second sensor):

Cut the veroboard into a 3x3 square (11x11mm) with a sharp knife or old side cutters.

Solder the 3 header pins, the resistor and either the photodiode or the reed switch to the board.

The photodiode should have its flat edge against the 3.3V pin.

Ensure the photodiode is on the opposite side of the board to the header pins so that it can be positioned flush against the LED on the meter, or that the reed switch has enough slack in the connecting wires to be easily positioned in the correct place on the meter.

[IMAGE PHOTODIODE]

[IMAGE REEDSWITCH]

Follow the quickstart for ESP-IDF to install the SDK and any dependencies. Install usb serial drivers (if necessary)

. $HOME/esp/esp-idf/export.sh (or where you installed the esp-idf SDK)

Clone this repository

cd meter_1_rate (if using one photodiode/reed switch)
or
cd meter_2_rates (if using 2 photodiodes)

idf.py menuconfig

Select "Meter Configuration":

• Enter the meter name, which is used as the MQTT topic prefix, e.g. electricity or gas
• WiFi network name (ssid)
• WiFi password
• MQTT broker URL
• Use Static IP: Un-checked
• Use Button debug: Checked

Connect the FireBeetle to the USB port of the computer.

idf.py build
idf.py -p /dev/cu.wchusbserial1410 flash # (replace the port with the correct one for your device)
idf.py monitor

Press the button marked with 27 (not the RST button) on the FireBeetle. The green LED will flash, and log entries will appear in the console. Find out the IP address assigned by looking for the log line starting got ip:, and configure your router so that the device is given a static IP address. This will save a lot of battery life by speeding up the WiFi connect process.

idf.py menuconfig

Select "Meter Configuration":

• Use Static IP: Checked
• Static IP address
• Gateway IP (IP address of your router)
• Netmask

idf.py build
idf.py -p /dev/cu.wchusbserial1410 flash # (replace the port with the correct one for your device)
idf.py monitor

Using a program such as MQTT Explorer, you can verify that the pulse count is being correctly published to {meter_name}/total, and the battery voltage to {meter_name}/battery. (Ensure you are connected before pressing the button).

If the count isn't received by MQTT, the debug level can be increased to show more information during the WiFi and MQTT connect process by changing the menuconfig: "Component Config" > "Log Output" > "Default Log Verbosity": "Verbose"

Install the final version of the software.

idf.py menuconfig

Select "Meter Configuration":

• Use Button debug: Un-checked

idf.py build
idf.py -p /dev/cu.wchusbserial1410 flash # (replace the port with the correct one for your device)

Before connecting the battery double check the polarity of the connector. If the red wire does not line up with the + symbol on the board, then use a tiny screwdriver to lift the tab to swap over the wires in the connector.

Connect the battery to the FireBeetle to charge it while connected via USB to the computer. The red light will be solid while charging, and will flash rapidly once charged. It should reach about 4.2V when fully charged. The battery should have protection to not discharge below 2.5 V, but to play it safe, this project is setup to report 0% battery and go into deep sleep when the voltage is below 3 V.

[IMAGE battery]

Edit your Home Assistant configuration.yaml to setup MQTT sensors to receive the meter values and battery voltage and percentage.

Replace "electricity" in the state_topic with the name you configured your MQTT topic prefix to be.

If necessary, replace 0.001 in the line containing value_template: "{{ value | float * 0.001 }}" based on how many impulses make a unit, as stated on the meter (e.g. 1 imp = 0.001kWh).

sensor:
  - platform: mqtt
    name: Electricity Meter
    unique_id: electricity_meter
    state_class: total_increasing
    device_class: energy
    state_topic: "electricity/total"
    unit_of_measurement: kWh
    value_template: "{{ value | float * 0.001 }}"
  - platform: mqtt
    name: Electricity Meter Battery Voltage
    unique_id: electricity_meter_battery_voltage
    device_class: voltage
    state_topic: "electricity/battery"
    unit_of_measurement: V
    value_template: "{{ value | float }}"
  - platform: mqtt
    name: Electricity Meter Battery
    unique_id: electricity_meter_battery
    device_class: battery
    unit_of_measurement: "%"
    state_topic: "electricity/battery"
    value_template: "{{ (([(value|float - 3), 1.2]|min / 1.2) * 100) | round(1) }}"

Restart Home Assistant for this to take effect.

3D Print the following files, depending on your setup:

• Case body
• Case insert (to separate the battery and the FireBeetle)
• Case lid for 1 sensor or Case lid for 2 sensors

and

• Photosensor body
• Photosensor lid

or

• Reedswitch body
• Reedswitch lid

Connect the photodiode or reed switch board to the FireBeetle, matching pins 3.3, GND and A3

[IMAGE SENSOR PINOUT]

[IMAGE CONNECTED BOARD]

If you're using a second sensor board, connect to the other 3.3, GND and A1 pins.

Install on the meter so the photodiode covers the LED or the reed switch is in the correct position to be triggered by the magnet in the dial.

It can help in positioning the reed switch to attach a multi-meter in continuity mode across the reed switch while the meter is turning.

[IMAGE CONNECTED TO METER]

You can monitor the battery percentage in Home Assistant, and when it gets low, connect a USB power bank to the USB port on the FireBeetle to recharge. As mentioned above, it will go into deep sleep if the voltage goes below 3 V.

Do not leave the battery connected but discharged below 3 V for a long time because it could damage the battery.

Current battery consumption is 3% in 10 days using a 1,100 mAh battery, so the it should last around a year before needing to be recharged.

Use the energy dashboard in Home Assistant to track your usage.

To track the cost of gas, convert the price per kWh to the price per m³ using the conversion formula given on your gas bill.