M1730-ESP32

ESP32 firmware that drives one or more M1730 analog panel meters (moving-coil ammeters) via PWM, with a web configuration UI and Home Assistant integration over MQTT.

Table of contents

• How it works
• Hardware
• Building and flashing
• First-time Wi-Fi setup
• Web UI
• MQTT / Home Assistant
• HTTP API
• Configuration reference

How it works

Each meter needle is controlled by a PWM signal on a GPIO pin. The firmware maps a physical value to a PWM duty cycle using a per-meter calibration table (reference value → duty %). With no calibration points defined, it falls back to a plain linear mapping scaled by the Max Duty percentage you calibrate for full-scale deflection. All settings are stored in LittleFS (/config.json) so they survive reboots.

With a calibration table:

duty %  =  linear interpolation between the surrounding (value, duty) points,
           falling back to the plain linear mapping outside the table

Without one (linear fallback):

needle position = (currentValue / 100) × (maxDuty / 100) × 1023 ticks

PWM runs at 0.5 kHz with 10-bit resolution (0–1023).

Physical range mapping

Each meter has configurable Min / Max values that define its physical range (e.g. 0–50 A). The firmware normalises to 0–100 % internally, but MQTT publishes and receives in physical units — Home Assistant never has to deal with percentages.

Hardware

Connect the meter coil (via a current-limiting resistor sized for full-scale) between a GPIO pin and GND. Find the correct resistor value by raising Max Duty slowly until the needle reaches full scale.

Here’s a list of suggested current-limiting resistors:

Building and flashing

The project uses PlatformIO.

# Build
pio run

# Flash
pio run --target upload

# Open serial monitor (115200 baud)
pio device monitor

Board target: esp32-s3-devkitc-1

First-time Wi-Fi setup

On first boot (or when stored Wi-Fi credentials are missing), the device starts an access point named M1730. Connect to it with any phone or laptop — a captive portal will appear automatically.

1. Enter your Wi-Fi SSID and password.
2. Optionally change the Device hostname (default: m1730).
3. Click Save. The device connects to your network and restarts.

After connecting, the device is reachable at:

• http://<nhostname>.local (default http://m1730.local) (mDNS, works on most local networks)
• http://<IP address> (shown in the serial monitor on boot)

Factory reset (forgot password)

If you lose the web UI password, reset the device 5 times in quick succession (press the EN button or cycle power 5× within a few seconds — before the boot completes). The firmware resets all settings to factory defaults except meter pin assignments and calibration (maxDuty), which are preserved. On acknowledgement, all connected meters sweep 0→100→0.

Serial output shows the progress:

[BOOT] reset count 1/5
[BOOT] reset count 2/5
...
[BOOT] reset count 5/5, triggering factory reset
[BOOT] factory reset triggered!
...
[BOOT] factory reset complete, restarting...

Web UI

Browse to the device address to open the configuration page.

Info panel

Shows the current hostname and IP address.

Hostname

Sets the mDNS name (<hostname>.local) and the MQTT device name. Saved across reboots.

Meters

Use the Meters dropdown to add or remove meters (1–8). Each meter has:

Click Save to persist all settings. Changing the meter count also triggers an immediate save and meter re-attach.

MQTT / Home Assistant

Enabling MQTT

In the MQTT section of the web UI:

Home Assistant auto-discovery

On connect, the device publishes discovery payloads to homeassistant/number/…/config. Each meter appears in HA as a Number entity with min/max taken from the meter’s configured physical range and a step of 0.1. The entities are grouped under a single HA device named after the hostname.

Value mapping

Internally the firmware works with a 0–100 % duty value. MQTT publishes and receives physical values — the percentage is transparently mapped to the meter’s Min–Max range:

physicalValue = percentage / 100 × (rangeMax - rangeMin) + rangeMin

For example, with Min=0 and Max=50, the slider at 50 % publishes 25.0 to MQTT, and a command of 25.0 on the /set topic moves the slider to 50 %.

Topics

<n> is the zero-based meter index.

Reconnection

The firmware probes the broker TCP port before attempting a full MQTT connect. If the broker is unreachable, it retries every 30 seconds without blocking the web server.

Example HA automation

automation:
  - alias: Show solar power on meter
    trigger:
      platform: state
      entity_id: sensor.solar_power_w
    action:
      service: number.set_value
      target:
        entity_id: number.m1730_solar
      data:
        value: "{{ trigger.to_state.state | float | round(1) }}"

# Values are in physical units — if the meter Min=0, Max=3000, the HA
# number entity directly accepts watts, no conversion needed.

HTTP API

GET /set?i=<index>&v=<value>

Immediately moves meter <index> to <value> (0–100), updates PWM, and publishes to MQTT. Used by the live slider on the web UI. The value is applied in RAM only and is not persisted to flash — it is lost on reboot. Use the config page or a retained MQTT /set command to set a value that survives a restart.

Returns 200 OK on success, 400 on bad input.

GET /

Returns the full HTML configuration page.

POST /config

Saves all configuration from the HTML form and re-applies PWM to all meters. Responds with the updated configuration page.

GET /export

Returns only the meters configuration (pins, names, units, ranges, max duty, calibration tables) as a JSON array. Network/MQTT/auth settings are not included. Used by the “Export to box” button on the /backup page.

POST /import

Replaces the meters configuration from a JSON array (same shape as /export). Payload is sent as a form field named json. The input is validated before being applied: field bounds are clamped, arrays/strings are length-limited, numbers must be finite, ranges must be ordered, and calibration points must be strictly increasing. Invalid input returns 400 with an explanation and changes nothing. Network/MQTT/auth settings are left untouched. On success it redirects back to the main configuration page.

GET /backup

Dedicated page with the meters export/import UI.

curl -u admin:pass -d "json=[{\"pin\":4,\"maxD\":72.5,\"name\":\"Solar\",\"unit\":\"W\",\"rangeMin\":0,\"rangeMax\":3000}]" http://m1730.local/import

Configuration reference

Config is stored as JSON in LittleFS at /config.json.

{
  "hostname": "m1730",
  "mqtt": {
    "enabled": true,
    "host": "192.168.1.10",
    "port": 1883,
    "user": "ha",
    "pass": "secret",
    "prefix": "m1730"
  },
  "meters": [
    {
      "pin": 4,
      "maxD": 72.5,
      "name": "Solar",
      "unit": "W",
      "rangeMin": 0.0,
      "rangeMax": 3000.0,
      "logS": false,
      "cal": [
        { "ref": 0.0, "duty": 0.0 },
        { "ref": 1500.0, "duty": 35.0 },
        { "ref": 3000.0, "duty": 72.5 }
      ]
    }
  ]
}

The file is written by the web UI and should not need manual editing. To reset to factory defaults (keeping pin/calibration), reset the device 5 times in quick succession. To erase everything including flash, use pio run --target erase.