EnergySnap

EnergySnap is an open source energy logger for single-phase homes: a battery-powered, portable device that measures your electricity consumption without touching the wires. It clips onto the main cable with a current clamp, logs data to a microSD card for anything from one day to several weeks, and transfers it via Bluetooth to a desktop app for analysis. No cloud, no subscriptions, no electrician-level installation.

Schematics (KiCad), BOM and firmware are fully documented and open, so anyone can build it, study it and customize it.

A “snapshot” of your consumption, when and where you need it

EnergySnap was born for those who need real data, not estimates: leave it in the electrical panel for a few days or weeks, collect the data and analyse peaks, night-time consumption and hourly profiles. Compact, affordable and designed to be replicated — a complete maker project, from the schematic to the firmware up to the analysis app.

From the clamp to the chart, in 6 steps

Real battery life

Who is it for

Professionals — solar designers sizing systems and storage on real consumption data; electricians diagnosing anomalous loads by observing the system for days; objective reports to hand to the customer, before and after the intervention.

Hobbyists & makers — understand how much and when your home really consumes, room by room; hunt down the “energy hogs” and standby loads that weigh on your bill; the perfect base for energy-monitoring and DIY home-automation experiments.

Why does it last so long? Between samples the ESP32 goes into deep sleep, and the microSD and analog front-end are powered off (power gating). Data is always safe on the card, even with a dead battery.

How the open source energy logger works

EnergySnap uses a non-invasive SCT-013-030 current transformer: you open the clamp, place it around the live conductor of your main line, and close it. Nothing is disconnected or cut. The clamp produces a small signal proportional to the current flowing through the cable.

An analog front-end biases the signal at half the supply voltage and filters it before it reaches the ESP32-WROOM-32E. The microcontroller samples the waveform, computes the RMS current and estimates the power drawn by the home. Every minute (configurable) it writes a timestamped record to a CSV file on the internal microSD card.

When the measurement campaign is over, you pair EnergySnap with your PC over Bluetooth Classic and download the data into the EnergySnap Desktop app, which turns raw samples into charts, daily totals and hourly breakdowns.

What you can learn from a measurement campaign

• Your real baseline: how much your home draws at night when “everything is off”, often the most surprising number.
• Peaks and their timing: when the oven, heat pump or washing machine push you close to your contractual power limit.
• Daily and hourly profiles: how consumption shifts between weekdays and weekends, mornings and evenings.
• Before/after comparisons: run one campaign, replace an appliance or change a habit, run another, and compare the numbers.
• Data for decisions: realistic input for sizing a photovoltaic system, a battery or a new electricity tariff.

All data stays with you: the CSV files can be exported, shared or opened in any spreadsheet.

Build it yourself

EnergySnap is a complete open hardware project. The KiCad schematics, PCB files, bill of materials, firmware and desktop app are all published on this page, so you can order the boards, solder the components and flash the firmware yourself, or study the design and adapt it to your needs.

The design deliberately uses common, affordable parts: an ESP32 module, a standard SCT-013 clamp, two AAA batteries and a microSD card. It is a good project for makers who want to learn analog signal conditioning, low-power firmware design and Bluetooth data transfer on a real, useful device.

Frequently asked questions

Do I need to cut or disconnect any wires?
No. The current clamp closes around the existing cable. However, the main cable is usually inside the electrical panel: if you are not comfortable opening the panel cover, ask a qualified electrician to place the clamp for you.

How long do the batteries last?
About 56 days with one sample per minute, and up to roughly 8.5 months in power-saving mode, on two AAA alkaline cells.

Does it work with three-phase systems?
EnergySnap is designed for single-phase home systems (230 V / 50 Hz). Three-phase installations would require one clamp per phase.

Does it need Wi-Fi or a cloud account?
No. Data is stored locally on the microSD card and downloaded via Bluetooth. Nothing leaves your home unless you decide to share it.

Can I modify the firmware?
Yes. The firmware is open source: you can change the sampling interval, the file format or add new features.