If you have ever tried to meter more than one circuit with PZEM-004T boards, you know the pattern: one board per circuit, one UART per board, a nest of wiring, and no shared timebase between them. The rbAmp UI series takes the other approach — one module, several metering channels, one I²C bus.
Each UI model is the same rbAmp Basic wattmeter front-end for SCT-013 split-core clamps, differing only in how many independent metering channels it carries:
| Model | Channels | Typical use |
|---|---|---|
| UI1 | 1 | A single circuit — one appliance, one feed, one sub-panel leg |
| UI2 | 2 | Two circuits — e.g. mains + solar, or two appliances |
| UI3 | 3 | Per-appliance metering of a small load group (HP / AC / EV) |
| UI5 | 5 | Several circuits from one point — a small distribution board |
| UI7 | 7 | A whole small panel, or three phases plus neutral and spares |
All five sit on the same I²C address space, so you scale a install two ways that combine: pick the channel count you need per location (UI1 → UI7), and still put several modules on one bus when a job outgrows a single module. That is the model behind our three-phase build (three UI modules, one ESP32) and the whole-panel project.
Why one bus beats a stack of boards
- One controller, one wire pair. Every channel — whether it is 1 or 7 — is read over the same two I²C lines. No extra UART per circuit, no per-board polling loop.
- A shared timebase. Because the modules share the bus, they can be latched together on a single General-Call frame, so per-channel powers are captured on the same mains period and sum coherently. (See Can I put several rbAmp modules on one I²C bus?)
- Host-agnostic. ESP32/ESPHome, Arduino, Raspberry Pi/Python, ESP-IDF — the same module, the same registers. Start from the Home Assistant Energy Dashboard in 15 minutes.
A word on accuracy — honestly
The rbAmp front-end computes true active power (mean of u×i, with per-channel phase compensation) and resolves ±0.5 % of reading per channel — but overall accuracy is only ever as good as the current sensor in front of it:
- With an SCT-013 split-core clamp (what the UI series is built for), the clamp sets the error budget — typically a few percent out of the box, tightening to ±0.5–1 % after a one-point calibration against a reference (supported in all four libraries).
- For a guaranteed ±0.5 % class, pair the front-end with rbAmp's factory-paired precision CT — module and clamp calibrated together, guaranteed for your unit.
We never quote a single headline accuracy without naming the sensor, and we never claim a summed multi-channel total is more accurate than a single channel.
Which one do I need?
Count the measurement points you want to see as separate numbers, then pick the smallest model that covers them — one appliance is a UI1, a small board is a UI3/UI5, a full small panel is a UI7. Need more points than one module carries? Add a second module on the same bus.
Roadmap items such as bidirectional import/export accounting are noted as in development and are not part of the shipping UI series today.
👉 See the full model table, photos and variants on the product page: rbAmp UI-series wattmeter module (SCT-013)
New to CT metering? Start with How CT Energy Measurement Really Works, or see the rbAmp FAQ for wiring, addresses and bus limits.