Current Sensing with Esp32

Project description #

Attempting to use the esp32 to sense when my table saw is on and using homeassistant to turn on and off my dust collector.

I first attempted to use off the shelf shelly switches, but the current draw was too high. I would burn them out.

12-15-2024
- Tested circuit - I can see the change of the voltage on the GPIO1 pin, seems to go down when current is applied
- Looking into MQTT for homassistant integration, see video in web references
- Would like to use off-the-shelf tasmoto to simplify setup
12-29-2024
- Got it working by kind of buteforcing myself around the problem.
- Set GPIO1 to be ADC input
- ran command in the tasmodo console: AdcParam 1,0,743,0.121,1.5
- got most of the values from here but adjusted the 3rd and 4th and 5th params.
  - Arrived at the values by adjusting the 4th to work fior 120 volts
  - For the third, I pluggin in an electric kettle and got the real values from an inline power meter like this Once I had them I adjusted the third param until the numbers on the tasmodo web page were approxmatly the same.
  - Set the last param to where It would read as 0 when the kettle was off, but would still detect when on. Might need adjusted when deployed.
01-01-2025
- Tested Mini Step-Down Power Supply Module
  - turns out I need to power the s2 mini from the vbus bin and I need 5v, so no need to split the voltage
  - Used heat shrink tubes and WAGO 221 Lever Nuts to attempt to keep it safe.
  - Acknowledge that I need to use fuses and such to make it safer “in production” - reference

AC Current Sensor Split-Core Clamp Current Transformer
HiLetgo 3pcs ZMCT103C 5A AC Current Sensor Current Transformer
- might be able to use this for < 5 amp applications. )
esp32-s2mini
- documentation website
- Datasheet
Mini Step-Down Power Supply Module
- I think that I can use something like thios to make this so I can put it all in the same box and not have to worry about a power supply.

Function:
The CT sensor measures AC current passing through a conductor.
Output:
The SCT-013-030 outputs a small AC voltage proportional to the current being measured.

The CT sensor requires a burden resistor across its output terminals to convert the current signal into a measurable voltage.
Capacitor (10µF):
- Smooths the AC signal.
- Filters out high-frequency noise and stabilizes the voltage signal.

The ESP32 ADC input cannot accept negative voltages.
To prevent this, the circuit creates a voltage bias at half of the ESP32’s supply voltage (1.65V for 3.3V systems).

Resistor 1 and Resistor 2 form a voltage divider that creates a steady 1.65V reference point.
The AC signal from the CT sensor oscillates above and below this 1.65V midpoint.
This ensures the entire waveform stays within the ESP32’s ADC range (0V to 3.3V).

Pin	Purpose
ESP32 ADC IN (Pin 34)	Reads the conditioned voltage signal.
ESP32 GND	Common ground for the circuit.
ESP32 3.3V	Powers the voltage divider (biasing).

AC Signal Processing:
- The CT sensor outputs an AC voltage signal proportional to the measured current.
- The burden resistor converts current to voltage.
- The capacitor smooths noise.
- The voltage divider shifts the signal to center it around 1.65V.
ADC Reading:
- The ESP32 reads the biased AC signal.
- The signal oscillates above and below 1.65V but stays within 0V-3.3V.
Software Processing:
- Remove the DC bias (1.65V) in software.
- Sample the waveform to calculate the RMS value.
- Use the CT sensor’s calibration constant to convert the voltage reading to current.

Component	Function
CT Sensor	Detects current and outputs AC voltage.
Burden Resistor	Converts current to voltage.
Capacitor (10µF)	Smooths the signal and reduces high-frequency noise.
Voltage Divider	Creates a 1.65V bias for the AC signal.
ESP32 ADC	Reads the conditioned voltage signal.