• Micropython Amperage Monitor
  • Introduction
  • Microcontroller
  • Cabling
    • Dupont 3x Connector
    • Analog Output to Amperage for ACS5712
  • Files
  • Configuration
    • ADC Configuration Options
  • Operation
  • CMD Examples
  • Data Responses

View our load testing series here: https://www.learningtopi.com/category/load-testing/

This project utilizes a hall effect based linear current sensor and reports the information to a device connected on a UART interface (separate from the REPL console).

The sensor used is a Gikfun 20A based on an ACS712 module. This module is capable of reading -20A to +20A and is available from Amazon. The specifications for the ACS712 module can be found HERE.

The initial release will use an analog-to-digital (ADC) interface on an ESP32 microcontroller. Future releases may include other microcontrollers (i.e. RP2040).

⚠️ The ACS712 outputs up to 5V on the signal line and ESP32/RP2040 microcontrollers are only 3.3V tolerant. Please review the cabling section below and verify before applying more than an a couple of amps through the sensor

The ACS712 sensor has a 5V VCC input, signal out, and ground available via dupont jumpers on one end of the board. On the other are 2x screw terminals for the line to monitor.

Insert a diagram here!

The screw terminals should be connected inline with the ground from the device that you intend to monitor the amperage draw from. As the microcontroller maxes as 3.3V, the polarity of the cables matter!

The table below shows the voltage at different amperage levels.

Since the ACS5712 is capable of reading positive and negative amperage, we need to make sure that the terminals are connected to read our DC current as "negative". Otherwise at approx 6amps we will exceed the 3.3V limit on the ESP32. The best way to verify is to test. Get a baseline reading with no load, then tests again with 1-2 amps of load. If the output reads over 2.5v, switch the polarity.

The project contains several files, all of which are outlined here:

The configuration is all applied via a json file copied to the microcontroller. A sample json file is included in the project named config-sample.json.

Be sure to rename your file as "config.json" before copying to the microcontroller!

{
    "network": {
        "ssid": "******",  
        "psk": "******"
    },
    "adc": {
        "baseline_time": 30, 
        "interval": 100, 
        "timeout": 30, 
        "avg_count": 5, 
        "pins": [
            {
                "name": "sensor1pin32",
                "pin": 32,
                "atten": 11,
                "zero_voltage": 2.5,
                "max_voltage": 3.3,
                "max_adc_read": 4095,
                "max_amperage": 20
            }
        ]
    },
    "uart": {
        "uart": 2,
        "baudrate": 115200
    },
    "ntp_server": "192.168.1.1",
    "timezone": -7,
    "timezone_name": "PST",
    "logging_console": 7,
    "webrepl": {
        "enabled": true,
        "password": "test123"
    }
}

The configuration file is broken down into sections. The "network" section can be removed from the configuration if WiFi is not needed, however this will aso require the removal of the NTP and WebREPL configuration as well. Network, timezone, and WebREPL are self explanitory. The "logging_console" configuration sets the logging level for the Micropython REPL. 0-7 is supported (emergency - debug). See the loglevel.py file for number to name mappings if needed.

The ADC and UART configuration is outlined below:

The ADC (analog-digital-converter) options are broken into two groups. Settings that apply to all ADC pins, and settings that apply to a single ADC pin. The project is designed to support multple ADC inputs.

Global ADC configuration is applied under the "adc" dict as follows:

Per Pin configuration is applied as a dictionary object in the "pins" list:

UART configuration provides the serial connectivity to the host that will be sending commands and receiving logging data from the microcontroller.

NOTE: The UART described here is in addition to the standard REPL serial interface.

The plan is to add IP connectivity as an option for connectivity at a later date

For connectivity to the monitoring system, I am using a CP2102 based USB to TTL module available on Amazon.

Once the configuration is in place the microcontroller will come up into an idle state until commands are received from the monitoring station. The intent here is a baseline should be run with no load on the sensor PRIOR to connecting the equipment to be monitored. This will ensure the most accurate reading.

The following commands are accepted by the microcontroller over the UART interface configured above.

All commands from the management station must begin with "CMD:..." and end with a newline character.

Using a management station (in my case a Raspberry Pi 4B) connected to the microcontroller UART (via the CP2102 usb to TTL), the following Python can be used to send commands and receive data.

The python code requires the pySerial package

pip3 install -U pyserial

The following python will open the connection, get the status and configuration, as well as send the init and start commands. All text commands need to be encoded prior to sending.

import serial
ser = serial.Serial('/dev/ttyUSBX', baudrate=115200)
ser.write('CMD:CONFIG\n'.encode())
ser.read(ser.in_waiting)
>>> b'CONFIG:100:30:30:32:sensor1pin32:2828\n'
ser.write('CMD:STATUS\n'.encode())
>>> b'STATUS:READY:0\n'
ser.write('CMD:START:5\n'.encode())
>>> b'START:707603457\nDATA:sensor1pin32:0:0.7413919:[0, 0, 0]:0.0\nDATA:sensor1pin32:117:0.6640293:[0, 0, 0.6640293]:0.2213431\nDATA:sensor1pin32:247:1.018608:[0, 0.6640293, 0.7413919]:0.4684738\nDATA:sensor1pin32:373:1.998535:[0.6640293, 0.7413919, 1.018608]:0.8080098\nDATA:sensor1pin32:497:0.7413919:[0.7413919, 0.7413919, 1.018608]:0.8337973\nDATA:sensor1pin32:617:0.9025641:[0.7413919, 0.9025641, 1.018608]:0.8875215\n...<output omitted>...STOP:707603462\n'

All data is returned in a similar format to the CMD messages: