Sequent Microsystems 8-Relays-8-In-V1.0 Schematic

Backpanel Connector

The backpanel connector (J6) provides interfaces for various signals including SDA, SCL, ID0-ID2, PANIC, SPARE, and INT. It connects to a 3.3V power source and is designed to interface with a processor.

An output switch circuit is also shown, connected to +5V and routed to the processor.

RS485 Interface

An RS485 interface is implemented using an IC (U2) with connections for 485A, 485B, 485-RX, 485-TX, and LEDON. It is powered by 3.3V and includes resistors (R4, R5, R6, R7) and capacitors (C1) for signal conditioning and stability.

Power and OLED Interface

The board utilizes a voltage regulator (U3) for power management, converting +24V to +5V and then to 3.3V. It includes input/output pins for power and ground, along with capacitors (C2, C3) for filtering. An OLED socket (H1-H8) is also present for display connectivity.

LED Drivers

Two 74HC595PW shift registers (U4, U5) are used to drive multiple LEDs. Each shift register is connected to a 3.3V power source and receives serial data (DS), clock (SHCP), latch (STCP), and output enable (OE) signals from the processor. Resistors (RN1.1-RN1.4, RN2.1-RN2.4, RN3.1-RN3.4, RN4.1-RN4.4) are used in series with each LED for current limiting. The schematic shows connections for LEDs D3-D18.

Processor Interface

The STM32G030C8T6 microcontroller (U6) serves as the central processing unit. It interfaces with the backpanel connector, RS485 transceiver, and the LED drivers. The processor operates at 3.3V and includes connections for various GPIO pins, serial communication (SDA, SCL), SWD debugging (SWDIO, SWCLK), and power. External components like an 8MHz crystal oscillator (X1) with load capacitors (C6, C7, C8, C9) are used for clock generation, and a reset circuit is also included.

Input Circuits

Eight input channels (IN1-IN8) are implemented using optocouplers (EL357N(B)(TA)-G, U7-U14). Each input channel is connected to a 3.3V source through a pull-down resistor (R8-R15) and an optocoupler. The optocouplers provide electrical isolation between the input signals and the processor. The inputs are labeled 1001-1016, corresponding to the input channels.

Relay Outputs

Eight relays (REL1-REL8) are controlled by the processor via MOSFETs (L2N7002, Q2-Q9). Each relay is connected to a +24V power source. The gate of each MOSFET is driven by a processor output pin (GREL1-GREL8). Flyback diodes (D19-D26) are included across each relay coil to protect the MOSFETs from voltage spikes. The relays are connected to output terminals J4 and J5.