UpaSmartHome
Raspberry Pi 4 & 5 8-Channel Relay Board Complete Wiring & GPIO Pinout Guide
Step-by-step wiring diagram, GPIO pinout mapping, optocoupler isolation, and safety instructions to connect an 8-channel relay board to a Raspberry Pi 4 or 5.
An 8-channel relay board (such as the popular Waveshare 8-channel HAT or standard optocoupler-isolated relay boards) is the heart of physical home automation. It enables your Raspberry Pi 4 or Raspberry Pi 5 to switch high-power circuits — such as hydronic heating zone valves, circulation pumps, garage doors, motorized gates, and high-voltage lighting circuits — safely and reliably.
GPIO Pinout & Connection Mapping
Standard Raspberry Pi 40-pin header assignments recommended for 8-channel relay automation:
| Relay Channel | Raspberry Pi GPIO (BCM) | Physical Header Pin | Default Logic State |
|---|---|---|---|
| VCC (Logic Power) | 5V DC Power | Pin 2 or Pin 4 | Continuous +5V |
| GND (Ground) | Ground | Pin 6, 9, 14, 20, 25, 30, 34, 39 | Ground Reference |
| IN1 (Relay 1) | GPIO 5 | Pin 29 | Active Low / High |
| IN2 (Relay 2) | GPIO 6 | Pin 31 | Active Low / High |
| IN3 (Relay 3) | GPIO 13 | Pin 33 | Active Low / High |
| IN4 (Relay 4) | GPIO 16 | Pin 36 | Active Low / High |
| IN5 (Relay 5) | GPIO 19 | Pin 35 | Active Low / High |
| IN6 (Relay 6) | GPIO 20 | Pin 38 | Active Low / High |
| IN7 (Relay 7) | GPIO 21 | Pin 40 | Active Low / High |
| IN8 (Relay 8) | GPIO 26 | Pin 37 | Active Low / High |
Optocoupler Electrical Isolation & Power Jumper (JD-VCC)
Most quality 8-channel relay boards feature optical isolation (EL817 optocouplers) and a 3-pin jumper labeled JD-VCC / VCC / GND:
- With the Jumper Installed (Shared Power): The relay coils are driven directly from the Raspberry Pi's 5V rail. This is fine for testing 1 or 2 relays, but when all 8 relays energize simultaneously, coil current exceeds 600mA, which can induce brownouts, SD card corruption, or spontaneous reboots.
- With the Jumper Removed (Isolated External Power): Remove the blue jumper between
JD-VCCandVCC. Connect an external 5V 2A DC power supply's positive lead directly toJD-VCC, and external GND to relay GND. Connect the Raspberry Pi's 3.3V or 5V to the board's logicVCC. The Raspberry Pi's CPU is now 100% optically isolated from coil voltage spikes and inductive kickback.
Understanding Terminal Contacts: NO, NC, and COM
Each channel has three screw terminals on the high-voltage side:
- COM (Common): Feed your incoming line voltage (or low-voltage signal) here.
- NO (Normally Open): Disconnected when the relay is unpowered. When the relay triggers, COM connects to NO. Use this for standard lights, irrigation valves, and exhaust fans so they remain OFF when power is cut.
- NC (Normally Closed): Connected when the relay is unpowered. When triggered, the circuit opens. Ideal for fail-safe heating valves that must open if control power is lost.
Instant Testing from Raspberry Pi Terminal
On modern Raspberry Pi OS Bookworm (or Raspberry Pi 5 using RP1 I/O controller):
# Turn Relay 1 ON (GPIO 5 active low)
pinctrl set 5 op dl
# Turn Relay 1 OFF
pinctrl set 5 op dhZero-Code Setup with UpaSmartHome
With UpaSmartHome, you do not need to write custom Python scripts or manage background cron tasks. The platform natively detects the 8 GPIO channels, exposes them as interactive toggles in the mobile app, connects them with automated thermostat schedules, and makes all 8 switches voice-controllable via Apple HomeKit and Google Home.