whatwatt Go¶

Read smart-meter data locally and integrate it with your own systems.

whatwatt Go is a compact smart-meter interface device. It reads measurement data from a compatible electricity meter and makes the processed data available through local integration interfaces such as REST, MQTT and Modbus TCP.

Firmware 2.0.0 also introduces the Berry scripting environment for running custom integration logic directly on the device.

Why use whatwatt Go?¶

	Without a local meter interface	With whatwatt Go
Data access	Often limited to the meter display, utility portal or provider API	Local access through supported device interfaces
Update interval	May be delayed or aggregated by an external service	Determined primarily by the meter, protocol and configured reporting interval
Local integration	May require a vendor-specific ecosystem	REST, MQTT and Modbus TCP interfaces
Data processing	Usually performed by an external service	Measurements are parsed and normalised by the device
Automation	Usually implemented in another controller or cloud service	Actions and, in firmware 2.0.0, Berry scripts can run on the device

How it works¶

graph LR
    SM["🔌 Compatible smart meter"] -->|P1 / M-Bus / TTL / pMEP| WW["⚡ whatwatt Go"]

    WW -->|REST API| REST["🌐 Applications\nDashboards\nCustom software"]
    WW -->|MQTT client| MQTT["📡 MQTT broker\nHome automation\nIoT platforms"]
    WW -->|Modbus TCP slave| MB["🏭 SCADA\nEnergy management\nIndustrial controllers"]
    WW -->|Berry scripts| BERRY["⚙️ On-device\nintegration logic"]

    style WW fill:#3b82f6,color:#fff,stroke:none
    style SM fill:#64748b,color:#fff,stroke:none
    style REST fill:#10b981,color:#fff,stroke:none
    style MQTT fill:#f59e0b,color:#fff,stroke:none
    style MB fill:#8b5cf6,color:#fff,stroke:none
    style BERRY fill:#ef4444,color:#fff,stroke:none

whatwatt Go connects to a supported customer interface of the smart meter. Depending on the meter and installation, this can be:

P1,
M-Bus,
UART/TTL, including supported Kamstrup HAN configurations,
pMEP.

The device identifies and parses supported meter protocols, converts the received values into a common internal representation and exposes the available measurements through configured integration services.

The exact set of values and their update interval depend on the connected meter, its configuration and the protocol used.

Quick Start¶

The examples below assume that the device is available at 192.168.1.100.

A device can also be discovered through mDNS. Its hostname follows this pattern:

whatwatt-XXXXXX.local

XXXXXX represents the last six hexadecimal characters of the device identifier.

When WebUI password protection is enabled, API requests require HTTP authentication. Using --anyauth allows curl to negotiate the authentication method supported by the installed firmware.

REST APIMQTTModbus TCPBerry Scripting

Use the REST API for on-demand measurements, status information and device configuration.

# Read device, network and meter status
curl http://192.168.1.100/api/v1/system

# Read the latest available meter report
curl http://192.168.1.100/api/v1/report

With password protection enabled:

curl --anyauth -u ":PASSWORD" \
  http://192.168.1.100/api/v1/system

/api/v1/system can be used even when no valid meter report is currently available. The contents of /api/v1/report depend on the values supplied by the connected meter.

→ First REST Request · → REST Polling · → REST Streaming

whatwatt Go operates as an MQTT client and publishes data to a broker configured by the user.

# Run this command on a system that can access your MQTT broker.
# Replace the broker address and topic with your own configuration.
mosquitto_sub \
  -h 192.168.1.20 \
  -t "lab/energy/#" \
  -v

MQTT requires:

an MQTT broker reachable from whatwatt Go,
a configured broker address and port,
a configured publication topic,
optional credentials or TLS certificates when required by the broker.

The MQTT payload can be adapted using the device's payload-template configuration.

→ MQTT Guide · → Secure MQTT

Modbus TCP provides read-only register access for compatible industrial and energy-management systems.

Enable the Modbus TCP slave service before attempting to read registers. The default TCP port is 502, unless another port has been configured.

# Example: read ten 32-bit floating-point values from input registers.
# The correct start address and count depend on the active register map.
mbpoll -B -t 3:float -c 10 -0 -r 0 192.168.1.100

The Modbus implementation:

operates as a Modbus TCP slave,
supports function code 04 — Read Input Registers,
uses read-only input registers,
supports a default register map,
supports custom register maps,
supports configurable numeric types and scalers,
uses big-endian byte and word order.

The active register map should always be checked before configuring a Modbus client.

→ Modbus TCP Guide · → Modbus Examples

Firmware 2.0.0 includes a Berry scripting engine for implementing integration logic directly on the device.

Scripts can react to meter reports, execute periodic functions, make HTTP or HTTPS requests, perform Modbus TCP transactions and call selected local APIs.

import ww

def on_report(report)
    if report and report.energy
        if report.energy.active and report.energy.active.positive
            var total_energy = report.energy.active.positive.total
            print("Imported active energy:", total_energy)
        end
    end
end

ww.onreport("on_report")

The structure of a report passed to a script depends on the measurements available from the connected meter.

An external USB-C power supply is recommended for continuous script execution, particularly when several communication services are enabled.

→ Berry Scripting Guide

Choose an Integration Method¶

flowchart TD
    Start["Integrate whatwatt Go"] --> Q1{"How should data be obtained?"}

    Q1 -->|"On demand"| REST["REST API polling"]
    Q1 -->|"Continuous updates"| Q2{"Is an MQTT broker available?"}
    Q1 -->|"Industrial registers"| MB["Modbus TCP slave"]

    Q2 -->|"Yes"| MQTT["MQTT publication"]
    Q2 -->|"No"| SSE["REST streaming"]

    REST --> Q3{"Is custom logic required<br/>on the device?"}
    MQTT --> Q3
    SSE --> Q3

    Q3 -->|"Yes"| BERRY["Berry scripting<br/>or Actions"]
    Q3 -->|"No"| DONE["Integration complete"]

    MB --> DONE
    BERRY --> DONE

    style Start fill:#3b82f6,color:#fff,stroke:none
    style REST fill:#10b981,color:#fff,stroke:none
    style MQTT fill:#f59e0b,color:#fff,stroke:none
    style MB fill:#8b5cf6,color:#fff,stroke:none
    style BERRY fill:#ef4444,color:#fff,stroke:none
    style SSE fill:#10b981,color:#fff,stroke:none

REST API¶

Choose REST when an application needs:

the latest available report on demand,
device status or diagnostics,
configuration access,
a straightforward HTTP/JSON integration.

MQTT¶

Choose MQTT when:

an MQTT broker is already available,
measurements should be published automatically,
several consumers need to receive the same data,
event-driven processing is preferred.

Modbus TCP¶

Choose Modbus TCP when integrating with:

SCADA systems,
energy-management controllers,
charging or photovoltaic equipment that can read Modbus TCP input registers,
industrial software based on register maps.

Compatibility with a particular third-party product depends on its ability to use the configured function code, register addresses, data types, scaling and byte order.

Berry and Actions¶

Choose on-device automation when logic should execute directly on whatwatt Go.

Berry is intended for programmable integrations. Actions provide configured HTTP or Modbus operations without requiring a complete custom firmware build.

Documentation Map¶

Getting Started¶

Page	Description
Overview	Device capabilities and available integration methods
REST vs MQTT	Comparison of REST and MQTT integration models
First Request	Initial REST API connectivity test
Power & Wi-Fi	Power-budget and network considerations
Device Discovery	mDNS and DNS-SD discovery
System Info	Device, network, meter and service status

Integration Methods¶

Page	Protocol	Typical use
REST Polling	HTTP/JSON	On-demand reads and dashboards
REST Streaming	SSE	Continuous HTTP-based updates
MQTT	MQTT	Broker-based telemetry
Secure MQTT	MQTT over TLS	Encrypted broker communication
Modbus TCP	Modbus TCP	Industrial and register-based integrations

Configuration and Automation¶

Page	Description
REST Conventions	Common rules used by configuration endpoints
Wi-Fi Setup	Wi-Fi client configuration
Berry Scripting	Programmable on-device integration logic
Actions	Configured HTTP and Modbus operations
SD Card Logging	Local CSV report storage

Reference¶

Page	Description
HTTP Basics	HTTP methods, response codes and content types
curl Examples	Command-line request examples
OBIS Codes	Common measurement identifiers
Report Objects	JSON report structure and field descriptions
Availability and Licensing	Firmware, edition and service availability notes

System Integrations¶

Page	System
Loxone	Loxone integration guidance

Supported Smart Meters¶

whatwatt Go supports several customer-interface and protocol combinations. Compatibility should be determined from the meter model, installed communication module, enabled customer port and meter configuration.

The following examples are included in the published compatibility documentation:

Manufacturer	Example models or series	Interface or setup
Ensor	eRS301, eRS801	P1, RJ12
Iskraemeco	AM550 with supported CII module	P1, RJ12
Iskraemeco	IE.5	P1, RJ12
Kamstrup	Omnipower	TTL/KMP, requires whatwatt adapter
Kamstrup	Omnia	P1, RJ12
Landis+Gyr	E360	P1, RJ12
Landis+Gyr	E450, E570	M-Bus, RJ12
Meter+Control	Flexy	P1, RJ12
Echelon / NES	83335-3, generation 5	P1, RJ12
Echelon / NES	83334-3, generation 4	pMEP, installation-dependent
Echelon / NES	83332-3, generation 3	pMEP, installation-dependent
Sagemcom	S211, T211	P1, RJ12
Sagemcom	S210, T210-D	M-Bus, RJ12
Sagemcom	T310	P1, RJ12
Sagemcom	XT211	P1, RJ12
Semax / Elster	AS3000 with supported CII module	P1, RJ12
Semax / Elster	AS3500	P1, RJ12
Kaifa	MA309M	M-Bus, RJ12
Siemens	TD-351X	M-Bus, RJ12
smart-me	Nimbus	P1, RJ12

Some installations require:

activation of the customer interface by the utility,
meter encryption or authentication keys,
an adapter or communication module,
external USB-C power,
specific firmware support.

A standard interface alone does not guarantee that every meter variant or configuration is supported. Consult the current compatibility list or whatwatt support when a meter is not explicitly listed.

Firmware and Service Availability¶

Available functions depend on:

the installed firmware version,
device configuration,
hardware revision,
enabled services,
applicable commercial edition or service terms.

For example:

Modbus TCP slave support was introduced in firmware 1.2.20,
Berry scripting is a firmware 2.0.0 feature,
the device reports its firmware version through /api/v1/system,
newer firmware can expose license information such as .device.license.type and .device.license.activation_date.

Do not infer feature availability solely from the presence of a license field. Verify the installed firmware, service configuration and current product terms.

curl http://192.168.1.100/api/v1/system

With authentication enabled:

curl --anyauth -u ":PASSWORD" \
  http://192.168.1.100/api/v1/system

Local Operation and Data Control¶

whatwatt Go supports local data access through REST, MQTT, Modbus TCP, SD-card logging and on-device automation.

REST and Modbus clients can communicate with the device directly over the local network. For MQTT, measurement data is sent to the broker configured by the user; that broker may be local or remote.

The device can also use optional cloud and third-party integrations when they are enabled. Therefore, whether measurement data remains entirely within the local network depends on the selected configuration.

To maintain local-only operation:

use a broker hosted inside the local network,
disable unnecessary cloud integrations,
restrict outbound network access where appropriate,
protect the WebUI and API,
use TLS where supported and required,
review all enabled services before deployment.

The user determines which configured systems receive the available meter data.

Get Started Learn More

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📧 Support: whatwatt.ch/en/contact
📖 FAQ: whatwatt.ch/en/faq-and-support
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