SRM8 Serial Relay Module 8-Channel
SRM8 is an 8-channel relay module designed to allow expanding microcontroller I/O pins. SRM8 is based on the 8-bit shift register 74595 IC. It supports 8 output relays while using only three I/Os. SRM8 can be daisy-chained to further extend the outputs to theoretically an infinite number while still using the same three microcontroller I/O pins.
SRM8 module can be supplied from a wide range of voltages (5-40V). The input control signals are Digital Input (DI), Clock (CK), and Load (LD). Every time the shift register Clock input receives a low to high transition it accepts the data input value to bit0 and shifts the internal register data by one bit. Thus, 8 clock pulses are required to get one-byte data from the microcontroller. Finally, a latch pulse is required to load all internal shift register data to parallel outputs (Relays). This control sequence can be performed using a hardware-implemented SPI or a few lines of written code.
Features
- Supports: 8-channel output relays.
- Protocol: SPI.
- Wide operating voltage range: 5-40V (two selectable ranges).
- Input signals (TTL): Data Input (DI), Clock (CK), and Load (LD).
- Output signals (TTL): Data Output (DO), Clock (CK), and Load (LD).
- Power-on relay status is OFF (a reset operation is auto-applied up on power on).
- Green LED for power indication.
- Red LED indicator for each output relay.
- Both normal open and normal close terminals are available.
- Reverse polarity protection for power input.
- Input and output signals are available via screw clamp terminals as well as pin headers for flexibility.
- SRM8 module can be daisy-chained to obtain a large number of relay outputs.
- The power connector is duplicated to facilitate the daisy chain board-to-board power connection of up to 16 modules, To connect more SRM8 modules use external wiring.
- Mounting: Four (Ø 3.5mm) mounting holes for easy installation.
- Dimensions: 207 X 45 X 18mm.
Specifications
| Parameter | Value |
|---|---|
| Model | SRM8 |
| Channels | 8 relay outputs |
| Control Interface | Serial (74595 shift register) — DI, CK, LD (SPI compatible) |
| Supply Voltage | Wide range 5–40V (selectable ranges) |
| Power Connector | Duplicated for easy daisy-chain power up to 16 modules (board-to-board up to 16) |
| Indicators | 1× green power LED 8× red relay status LEDs |
| Contact Types | NO and NC terminals provided per channel |
| Protection | Reverse-polarity protection on power input |
| Signal Access | Screw-clamp terminals and pin headers for DI/CK/LD/DO |
| Mounting | 4 × Ø3.5 mm mounting holes |
| Dimensions | 207mm × 45mm × 18mm |
Applications
- Expanding microcontroller or PLC outputs for relay-based switching in automation systems.
- Controlling lamps, solenoids, motors and HVAC or lighting circuits in test rigs and control panels.
- Prototyping and classroom projects where many relay channels are needed with minimal wiring.
- Multi-module installations that require convenient chained expansion and centralized power distribution.
- Any low-voltage control system needing reliable, screw-terminal relay outputs.
Package Contents
- 1× SRM8 Serial Relay Module 8-Channel.
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