Overview

What is rbAmp

rbAmp is a compact hardware module for precision measurement of AC mains parameters over an I²C interface. It is built around a Cortex-M0+ microcontroller with an integrated isolated sensor front-end and factory-stored calibration.

From the integrator's point of view, rbAmp behaves like a standard I²C slave: apply power, read registers — receive ready-to-use physical-unit values (volts, amperes, watts). No signal processing is required on the master side.

What it measures

Quantity	Register (I0)	Type	Range	Accuracy
RMS voltage, U_rms	`0x86`	float32, V	0…300 V	±0.5%
Peak voltage, U_peak	`0x8A`	float32, V	0…450 V	±1%
RMS current, I_rms	`0x8E`	float32, A	0…100 A (SKU-dependent)	±0.5%…±1%
Peak current, I_peak	`0x9A`	float32, A	0…140 A	±1%
Active power, P	`0xA6`	float32, W (±)	±23 kW	±1%
Power factor, PF	`0xB2`	float32 (±)	−1…+1	±0.01
Reactive power, Q	`0xD0`	float32, VAR (±)	same as P	±2%
Line frequency	`0x20`	u8, Hz	45…65 Hz	±0.5 Hz
Time-averaged P over period	`0xDC`	float32, W	same as P	±1%

The full register map is detailed in Real-time polling and Period metering.

Applications

Tariff metering — energy billing in 1-min, 15-min, 1-hour, daily, monthly, or yearly intervals
Smart home — whole-house consumption monitoring, per-load sub-metering, generation tracking
Load control — feedback signal for power-regulating devices (water heaters, resistive loads, inverters)
Energy balancing — separate accounting of consumption and generation in homes with solar
Grid quality monitoring — both on the consumer side and on the utility side

Module variants

Variant	U	I channels	P	When to choose
UI1	yes	1	yes	single accounting point — whole-house meter, boiler, single inverter
UI2	yes	2	yes	two sub-meters on one phase (lights + outlets, generation + consumption)
UI3	yes	3	yes	three flows on one phase (maximum sub-metering granularity)
UI5 / UI7	yes	5 / 7	yes	high-channel-count phase monitoring (large panels, lab benches)
I1	no	1	no	current-only monitor (master computes P with its own U source)
I2	no	2	no	two-channel current monitor
I3	no	3	no	three-channel current monitor
I6 / I8	no	6 / 8	no	multi-channel current monitor

On I-only variants, active power is not computed (P_real = 0), and PERIOD_AVG_P_W returns 0. The master must either provide its own voltage source for power calculation, or use the current data alone.

Product tiers

rbAmp is offered in three product tiers. Each tier is a complete combination of hardware revision and firmware — not a firmware-only flag. Moving between tiers requires a physical SKU change, not a firmware update.

BASIC — entry-level product line

Hardware: cost-optimized analog front-end suitable for typical residential loads.
Firmware: unidirectional consumption metering. The per-period accumulator clamps each per-window active-power sample to zero before integrating: only positive (consumed) energy is counted, mirroring a classical mechanical disc meter that only spins forward.
PERIOD_AVG_P_W is always ≥ 0; reverse-flow events are dropped from the period accumulator.
Use cases: households without on-site generation; sub-metering of pure consumers (heaters, motors, appliances).

STANDARD — bidirectional product line

Hardware: extended analog stack supporting accurate measurement of both consumption and reverse flow.
Firmware: bidirectional metering. Two separate accumulators per period — one for consumption, one for export — exposed as two register groups (PERIOD_AVG_P_W and PERIOD_AVG_P_NEG_W).
Use cases: homes with rooftop solar, wind generators, battery storage, regenerative loads, V2G EV chargers.

PRO — premium product line

Hardware: PRO-grade analog front-end (lower noise, tighter linearity), premium factory calibration, optional extended channel sets.
Firmware: bidirectional metering plus extended diagnostics (peak demand windows, harmonics indicators, drift monitoring registers).
Use cases: sub-metering for commercial tenants, billing-grade installations, instrumentation labs, energy-intensive industrial loads.

Where the tier shows up in this documentation

Throughout the chapters, features that depend on the tier are explicitly marked, for example:

STANDARD / PRO only — on a BASIC module this register is not available.

The base register block at 0x00..0xCF is identical across all tiers; the additional STANDARD and PRO registers reside above 0xCF.

Key features

I²C slave: 100 kHz (Standard mode) and 400 kHz (Fast mode), both validated
Address: 7-bit 0x50 by default, reprovisionable to the 0x08..0x77 range
DATA_READY (DRDY): optional open-drain pin, ~10 µs LOW pulse every ~200 ms, marks the moment when RT registers are coherent
Atomic period latch: command 0x27 freezes the per-period averaged power; one write closes and opens — no dropped or duplicated samples at the boundary
General Call (broadcast): address 0x00 for simultaneous command to all modules on the bus (available from firmware release 1.0)
Master-side time base: energy is computed master-side as avg_P × dt; eliminates per-module crystal drift in multi-module systems
Calibration in flash: factory calibration is stored in the on-chip flash; no user calibration is required for stock SKUs
Auto-configuration: the module starts measuring immediately after power-on (~250 ms to the first valid result)

Roadmap

Planned future SKUs (mentioned here for forward-compatible system design):

Model	Mains type	Channels	Status
rbAmp-U2I2	US split-phase 2×120 V	2U + 2I	planned
rbAmp-U3I3	True three-phase 380/400 V	3U + 3I	planned

The current documentation covers single-phase models only. The multi-phase API will be an extension of the existing register map — registers 0x86..0xEF of single-phase modules remain forward-compatible (extension, not replacement).

What rbAmp does not do

Does not integrate energy (Wh) internally — energy accumulation is the master's responsibility (see Period metering)
Does not drive loads, contain automation logic, or run programmable rules
Has no built-in display

Hardware connection — connection, power, wiring
Initialization — first power-on