03 · STD hardware and wiring

Signals an installer or integrator deals with on an STD module (STD-UI1, STD-U3I3). The full signal rules are in the hardware reference; this page is the practical summary.

The enclosure covers the lower part of the board, where the AC circuits are. The upper part of the board with the interface connector (VIN, GND, bus) is open; it is galvanically isolated from the AC part. The only terminal that comes out of the enclosure is the AC voltage-sensor terminal, in a plastic housing.

⚠ Safety. The measurement inputs connect to mains. Install the module in a closed electrical cabinet, by qualified personnel only. Switch the mains off before connecting or moving any wire.

Signal set

Voltage connection

The AC voltage input uses the same wire and fuse rule as BASIC: a thick wire is not required, AWG26–22 is enough; a fuse in the L line is mandatory, rated up to 0.1 A.

• STD-UI1: one voltage input.
• STD-U3I3: the voltage terminal block has four positions: N, L1, L2, L3. The module measures phase-to-neutral voltage, so the neutral is required. Fuse each L line you connect (up to 0.1 A).

Sensors

Every current channel ships with its own sensor, calibrated together with the channel and labelled with it. Connect each sensor to the channel it is labelled for. Moving a sensor to another channel, or connecting another sensor, loses the calibration. The sensors and the board are marked and the kit comes pre-connected; for the import direction follow the arrow marking on the sensor and the board.

Connector

The module has one JST XH 7-position connector, 2.54 mm pitch. Its signals are:

SDA and SCL are shared with the Modbus UART lines, so one connector serves both transports.

Choosing the transport

A 3-position interface mode switch on the board selects the transport at boot:

• Modbus RTU — Modbus RTU with the saved serial settings;
• Modbus default — Modbus RTU at 9600 8N1, unit id 1 (use it to reach a module whose serial settings are unknown);
• I²C — the module is an I²C slave at 0x50.

The switch is read only at start-up, so a change applies after a restart (power cycle or RST).

Sharing a bus with BASIC modules

BASIC and STD modules both answer at 0x50 by default. Change the address of one of them before putting both on one bus.

I²C pull-ups

Two jumpers on the PCB enable 4.7 kΩ I²C pull-ups to 3.3 V on the module. The connector logic is 3.3 V; VIN (5 V) feeds only the on-board regulator.

I²C wiring

• Open-drain bus; the pull-ups come from the master or from the two PCB jumpers. Recommended bus speed: 50 kHz on ESP32 and ESP8266 hosts (a limitation of the ESP-IDF I²C driver, not of the module), 100 kHz on other hosts; do not use 400 kHz. The speed is the user's choice.
• Set the master's SCL timeout to at least 10 ms: during firmware-update flash writes the module may stretch the clock for several milliseconds.
• DRDY is an open-drain output without a pull-up on the module; when you use DRDY, fit a pull-up on the master side — 10 kΩ to the master's 3.3 V logic supply is recommended. It idles high, a short low pulse for each new measurement window, held low on an alarm. Pair each pulse with the module's WIN_SEQ.

RS-485 wiring

• The module has no RS-485 transceiver: the connector carries UART TTL on pins 3 (module RX) and 4 (module TX), plus DE for an external transceiver. Termination and bias are external.
• If your RS-485 adapter needs turnaround time, set CFG_TX_DELAY (0…100 ms response hold-off).
• Out of the box: unit 1, 9600 8N1. Change the serial settings and unit id through the configuration registers; see Modbus transport.

RST

RST is the reset input of the module, for a hardware reset by the master; it may be left unconnected. Use it to recover a silent module or to apply an interface-switch change without a power cycle. A reset loses the state your master owns in RAM (event mask, thresholds, snapshot arming, clock); re-arm per the diagnostics checklist.

Status LEDs

Enclosure

The enclosure has a DIN clip and can be installed in a cabinet (DIN rail).