IoTextra Octal3
4 isolated digital inputs · 4 latching DPDT relays · galvanic isolation · 3750 VRMS
Inputs up to 36 VDC via GPIO · relay contacts 250 VAC / 220 VDC / 2 A · relay control via I²C → TCA9534A → DRV8837C
Part of the IoTextra series · compatible with IoTsmart and IoTbase · Open Hardware
This module is a member of the IoTextra series, which serves as a fundamental building block of our ecosystem and embodies the Make Things Happy Philosophy. It is engineered to bridge the gap between rapid prototyping and industrial-grade reliability.
Hardware Synergy: The module is compatible with both IoTsmart and IoTbase series.
Software Power: This hardware compatibility unlocks the full potential of the IoTflow platform, with native support for Tasmota and Home Assistant as well. It enables you to:
- Create custom Node-RED nodes effortlessly.
- Integrate via MQTT with third-party global platforms like Blynk.
- Scale your project from a single node to a complex industrial network.
Key Specifications
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Configuration: 4 digital inputs, 4 latching DPDT (2 Form C) relays (KEMET EC2-5SNU)
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Isolation: individual galvanic isolation per channel, 3750Vrms dielectric strength
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Digital inputs: up to 36VDC; logic thresholds 0–2V (logical "1"), 4–36V (logical "0"); read directly via AP0–AP3 on the HOST connector
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Relays: bistable/latching, retain state without coil power — no heat, no holding current, no unexpected switching on power failure. Switching capacity 2A at 250VAC/220VDC
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Relay driver: TI DRV8837C H-bridge, generates the polarity-reversal pulse, built-in flyback protection, no external diodes required
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Relay control: via I²C through the onboard TCA9534A expander; the shared nSLEEP signal (AP5) must be driven High before a switching pulse and returned Low afterwards to enable the DRV8837C drivers
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Relay state readback: not available in hardware — the microcontroller must store relay state in EEPROM/flash and restore it on boot
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I²C addressing: DIP-switch (A0–A2), up to 16 modules on one bus (each requiring its own or a shared nSLEEP signal)
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Connectors: HOST, Qwiic × 2
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Status indication: LED per digital input channel, LED per relay (LD_K1–K4)
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Size: 47 × 56 mm, with mounting holes for base-module or Raspberry Pi installation
Operation Modes
🔌 Standalone
Connect via the HOST connector cable or Qwiic I²C connectors from any host microcontroller.
🧠 Smart
An IoTsmart module is inserted vertically into the HOST connector. Input reading, relay control, and the 5V module supply are provided through HOST, powered from the IoTsmart module.
🏗 Mezzanine
The module is installed into an IoTbase carrier board. Input reading, relay control, and the 5V module supply are provided through HOST.
Applications
⚡
IIoT — Control Cabinet Management
Digital inputs monitor circuit breakers and voltage presence; latching relays hold contactors or disconnect switches through power outages with zero coil energy consumption.
📡
Telecommunications — Bypass & Line Switching
Physical bypass switching of backup lines; relays remain in position indefinitely without holding current — critical for equipment running continuously for years.
🌱
Smart Farming — Irrigation Control
Monitor water level sensors and valve limit switches; activate irrigation valves with a short pulse and hold open with zero energy — ideal for solar-powered installations.
🏠
Smart Home — Blinds, Gates & Dampers
Connect position sensors and manual buttons to inputs; relays retain last position after a power cut — no unexpected movement on power restoration.
