I recently bought a unbranded WiFi Dual CT Clamp Meter from Aliexpress.
I need it to replace a Tomzn DIN Power Meter (from Aliexpress too) for two reasons: safety and completeness. This meter is not invasive, it doesn’t interfeere with electrical system.
These are all cheap chinese board so better not trust them too much.
The DIN Power Meter uses a shunt resistor to measure current but it cannot distinguish the power “direction”. I’m not able to know if my plug & play solar panel is producing enough power and current is flowing into electric network.
I received in cheap brown box with some label on it: PJ1203A is the model number and it’s Tuya based.
Well, i don’t particularly like Tuya but i already know there are many options to avoid it.
The last chance is to replace the board with a ESP but.. let’s keep it for later.
First of all, let’s try it. I connect it to power, install first Clamp, connect it to WiFi and it works.
I immediately see some kind of chinglish words indicating consumed/produced power.
I’m excited but.. it was too easy.
I configure HomeAssistant using LocalTuya to see all the data and i find the first big issue.
There is no entity indicating current “direction” and the Power value never goes below 0, it’s always a positive number even if power is going towards electrical supplier.
This means this product is unuseful for me since i need precise data.
I can’t continue working with Tuya so.. let’s open it.
There’s an MCU underneath the board and a very common esp-like board.
It’s a CB2S and it’s not an ESP. In fact it’s a BK7231N based board. It’s very common today to see this kind of boards since they should be cheaper than ESP.
I start by desoldering the board from the “extender board”, wire up my USB UART adapter to VCC (3.3v), GND, TX1 and RX1.
Open LTChipTool (which is a software made specifically for this board) and dump the firmware. This procedure is quite easy, you just need to connect for a bit the CEN pin on the board to Ground. ( Do not keep it connected, just keep it grounded for 1-2 seconds ).
Reading starts and after a minute or so i have the firmware backup in my hand.
LTChipTool has now a great feature which analyzes firmware dump and tries to extract configuration from the chip and Tuya Servers. It even generate a yaml configuration file for ESP Home with all sensors, inputs, switches, led and much more!
This worked great on this particular device since all the data is produced from a different chip and it just send data using TuyaMCU protocol to the BK7231N board. This means ESP Home just need to know which data is what and that’s it.
I’m not sure it could be as precise for different implementations which required some calculations.
Before wasting too much time i flash a basic ESP Home firmware. Since this is the first time i flash ESP Home on a non-ESP device, i want to try and also send an OTA update to make sure everything works as expected.
I generate a ESP Home item in HomeAssistant, set my board type and download a .uf2 file (from many options available) to be able to flash it with LTChipTool.
Flashing procedure is the same as reading: ground CEN for some time and it flashes the chip.
After flash i reboot it, wait some time and i see it on the network!
It works so let’s complete the ESP Home yaml with data generated from LTChipTool.
I clean it up, fix some bad translations, change some names and i send the OTA update.
Solder the board back up, closed the case and connect it back to power.
It works! Now i’m able to get all the data using a reliable ESP Home firmware, avoid a cloud connection which introduces trust and speed issues, and in case my internet connection goes down i can still get data from it.
At the end of this article you’ll find my YAML configuration for the board.
Considerations
It’s surprisingly easy to convert a Tuya device to ESP Home. LTChipTool does pretty much all the job.
That means you can easily convert also Smart Plugs, Smart light bulbs and everything else Tuya based.
YAML
esphome:
name: clamp-meter-2ct
friendly_name: Clamp_Meter_2CT
bk72xx:
board: generic-bk7231n-qfn32-tuya
# Enable logging
logger:
# Enable Home Assistant API
api:
encryption:
key: "======================================================"
ota:
- platform: esphome
password: "============================================================="
wifi:
ssid: !secret wifi_ssid
password: !secret wifi_password
# Enable fallback hotspot (captive portal) in case wifi connection fails
ap:
ssid: "Clamp-Meter-2Ct Fallback Hotspot"
password: "=================================================="
captive_portal:
web_server:
mdns:
button:
- platform: restart
name: Restart
debug:
update_interval: 3s
text_sensor:
- platform: debug
reset_reason:
name: Reset Reason
- platform: libretiny
version:
name: LibreTiny Version
- platform: template
id: tuya_direction_a
name: Direction A
filters:
- map:
- 0 -> Forward
- 1 -> Reverse
- platform: template
id: tuya_direction_b
name: Direction B
filters:
- map:
- 0 -> Forward
- 1 -> Reverse
sensor:
- platform: uptime
name: Uptime
- platform: tuya
sensor_datapoint: 101
name: Power A
unit_of_measurement: W
accuracy_decimals: 1
filters:
- multiply: 0.1
- platform: tuya
sensor_datapoint: 105
name: Power B
unit_of_measurement: W
accuracy_decimals: 1
filters:
- multiply: 0.1
- platform: tuya
sensor_datapoint: 106
name: Energy Forward A
unit_of_measurement: KWH
accuracy_decimals: 2
filters:
- multiply: 0.01
- platform: tuya
sensor_datapoint: 107
name: Energy Reverse A
unit_of_measurement: KWH
accuracy_decimals: 2
filters:
- multiply: 0.01
- platform: tuya
sensor_datapoint: 108
name: Energy Forward B
unit_of_measurement: KWH
accuracy_decimals: 2
filters:
- multiply: 0.01
- platform: tuya
sensor_datapoint: 109
name: Energy Reverse B
unit_of_measurement: KWH
accuracy_decimals: 2
filters:
- multiply: 0.01
- platform: tuya
sensor_datapoint: 110
name: Power Factor A
accuracy_decimals: 2
filters:
- multiply: 0.01
- platform: tuya
sensor_datapoint: 111
name: Frequency
unit_of_measurement: Hz
accuracy_decimals: 2
filters:
- multiply: 0.01
- platform: tuya
sensor_datapoint: 112
name: Voltage
unit_of_measurement: V
accuracy_decimals: 1
filters:
- multiply: 0.1
- platform: tuya
sensor_datapoint: 113
name: Current A
unit_of_measurement: mA
- platform: tuya
sensor_datapoint: 114
name: Current B
unit_of_measurement: mA
- platform: tuya
sensor_datapoint: 115
name: Total Power
unit_of_measurement: W
accuracy_decimals: 1
filters:
- multiply: 0.1
- platform: tuya
sensor_datapoint: 121
name: Power Factor B
accuracy_decimals: 2
filters:
- multiply: 0.01
uart:
rx_pin: RX1
tx_pin: TX1
baud_rate: 9600
tuya:
# DPIDs processed from schema model: ebtly8
on_datapoint_update:
- sensor_datapoint: 102
datapoint_type: enum
then:
- text_sensor.template.publish:
id: tuya_direction_a
state: !lambda "return std::to_string(x);"
- sensor_datapoint: 104
datapoint_type: enum
then:
- text_sensor.template.publish:
id: tuya_direction_b
state: !lambda "return std::to_string(x);"
number:
- platform: tuya
number_datapoint: 1
name: Forward Energy Total
unit_of_measurement: KWH
min_value: 0
max_value: 99999999
step: 1
- platform: tuya
number_datapoint: 2
name: Reverse Energy Total
unit_of_measurement: KWH
min_value: 0
max_value: 99999999
step: 1
- platform: tuya
number_datapoint: 116
name: Voltage Coef
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 117
name: Current A Calibration
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 118
name: Power A Calibration
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 119
name: Energy A Calibration Fwd
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 122
name: Frequency Calibration
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 123
name: Current B Calibration
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 124
name: Power B Calibration
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 125
name: Energy B Calibration Fwd
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 127
name: Energy A Calibration Rev
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 128
name: Energy B Calibration Rev
min_value: 800
max_value: 1200
step: 1
- platform: tuya
number_datapoint: 129
name: Report Rate Control
unit_of_measurement: s
min_value: 3
max_value: 60
step: 1
binary_sensor:
- platform: tuya
sensor_datapoint: 103
name: Tbd
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