# Industrial Embedded I/O Controller Board ## Description Industrial-grade embedded I/O controller schematic with 9-36V protected input, 5V buck, 3.3V logic, STM32F103C8T6 MCU, industrial dry/wet/pulse/analog inputs, 12V semiconductor-switched output, RS-485/UART communications, external watchdog, SWD/debug features, and interview-ready engineering notes. ## Project Details - **Owner:** samael33 - **Created:** 4/5/2026 - **Last Updated:** 4/5/2026 - **Visibility:** Public - **Implementation Details:** Sectioned industrial controller schematic with named power, input, communication, watchdog, debug, and protected output blocks. Net naming uses descriptive functional rails and signal names for PCB implementation and interview presentation. - **System Architecture:** flowchart TD VIN["9-36V Field Input"] --> PROT["Fuse Reverse Protection TVS"] PROT --> BUCK["5V Buck Regulator"] BUCK --> LDO["3.3V LDO"] LDO --> MCU["STM32F103 MCU Core"] LDO --> RS485["RS-485 Transceiver"] LDO --> WDG["External Watchdog"] LDO --> ANA["Analog Buffer and ADC Front End"] J2["Dry Input"] --> DIN["Dry Input Conditioning"] --> MCU J3["Wet Input"] --> ISO["Opto Input Conditioning"] --> MCU J4["Pulse Input"] --> ISO J5["Analog Input"] --> ANA MCU --> RS485 --> J6["RS-485 Field Connector"] MCU --> OUTDRV["High Side Output Switch"] --> J7["12V Output Connector"] MCU --> DBG1["SWD Header"] MCU --> DBG2["UART Debug Header"] WDG --> MCU - **Operating Voltage:** 9-36V input, 5V and 3.3V internal rails ## Key Components ### D1 — [SMBJ36A-13-F](https://www.flux.ai/lcsc/smbj36a-13-f~d9x.md) - Product Info Url: https://lcsc.com/product-detail/TVS_DIODES_SMBJ36A-13-F_SMBJ36A-13-F_C135070.html - Manufacturer Part Number: SMBJ36A-13-F - Role: TVS Diode - Role Details: Clamps positive surges on industrial VIN after reverse-polarity stage. - Package or Case Code: SMB_L4.6-W3.6-LS5.3-RD - Manufacturer Name: DIODES(美台) - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2304140030_Diodes-Incorporated-SMBJ36A-13-F_C135070.pdf - LCSC Part Number: C135070 - JLCPCB Part Class: Extended Part - Part Type: TVS - Package: SMB **Pins:** - A [pin 2] - C [pin 1] ### D2 — [SMAJ58A-13-F](https://www.flux.ai/lcsc/smaj58a-13-f~x3mp.md) - Manufacturer Name: DIODES(美台) - Manufacturer Part Number: SMAJ58A-13-F - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2304140030_Diodes-Incorporated-SMAJ58A-13-F_C110521.pdf - Role: TVS Diode - Package or Case Code: SMA_L4.4-W2.6-LS5.0-RD - Package: SMA - LCSC Part Number: C110521 - Part Type: TVS - Role Details: Clamps reverse-protection MOSFET gate-source stress on wide industrial VIN. - JLCPCB Part Class: Extended Part - Product Info Url: https://lcsc.com/product-detail/TVS_DIODES_SMAJ58A-13-F_SMAJ58A-13-F_C110521.html **Pins:** - A [pin 2] - K [pin 1] ### D3 — [SM712](https://www.flux.ai/lcsc/sm712~9760.md) - LCSC Part Number: C502564 - Package or Case Code: SOT-23-3_L2.9-W1.6-P1.90-LS2.8-BR - Datasheet URL: https://storage.googleapis.com/graviton-electric-symbols/document_assets/lcsc/2407101112_MDD-Microdiode-Semiconductor-SM712_C502564.pdf - Part Type: TVS - Forward Voltage: 0.45V to 0.55V - Role Details: Bidirectional TVS array across RS-485 A/B field lines for external surge and ESD robustness. - Manufacturer Part Number: SM712 - Role: RS-485 TVS - JLCPCB Part Class: Extended Part - Manufacturer Name: MDD - Diode Type: Schottky Diode - Package: SOT-23-3 - Max Reverse Voltage: 20V - Product Info Url: https://lcsc.com/product-detail/TVS_MDD-Microdiode-Electronics-SM712_C502564.html **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] ### F1 — [2016L050MR](https://www.flux.ai/adrian95/2016l050mr~9r5.md) - Manufacturer Name: Littelfuse Inc. - Manufacturer Part Number: 2016L050MR - Part Type: Fuse - Package: 2016 - Role: Resettable Fuse - Role Details: Limits sustained fault current at the 9-36V input ahead of downstream protection. - License: https://creativecommons.org/licenses/by/4.0/ - Current Rating: 20A - Datasheet URL: https://www.littelfuse.com/assetdocs/littelfuse_ptc_2016l_datasheet.pdf?assetguid=0a3f187e-62df-469f-85be-57fe3e3b4668 **Pins:** - P1 [pin 1] - P2 [pin 2] ### FB1 — [Ferrite Bead 0603](https://www.flux.ai/vasy_skral/ferrite-bead-0603~znt.md) - Role: Ferrite Bead - Part Type: Inductor - Package: 0603 - Role Details: Filters digital rail noise before the MCU analog supply pins. **Pins:** - ~ [pin 2] - ~ [pin 1] ### IC1 — [SGM2212-3.3XKC3G/TR](https://www.flux.ai/jecstronic/sgm2212-3p3xkc3gtr~l0g.md) - Manufacturer Part Number: SGM2212-3.3XKC3G_TR - License: https://creativecommons.org/licenses/by/4.0/ - Package: SOT-23-5 - Part Type: Integrated Circuit - Role: LDO Regulator - Manufacturer Name: SG Micro - Role Details: Generates clean 3.3V rail for MCU, watchdog, logic, and analog conditioning. - Datasheet URL: http://cn.sg-micro.com/uploads/soft/20220506/1651835177.pdf **Pins:** - GND [pin 1] - VIN [pin 3] - VOUT_1 [pin 2] - VOUT_2 [pin 4] ### IC2 — [VO4661-X007T](https://www.flux.ai/adrian95/vo4661-x007t~bt4.md) - Role: Optocoupler Interface - Datasheet URL: https://www.arrow.com/en/products/vo4661-x007t/vishay?region=nac - Manufacturer Name: Vishay - Part Type: Isolator - Package or Case Code: SOP254P1005X465-8N - Role Details: Dual-channel isolated field input receiver used for wet 9-36V and pulse input conditioning. - Manufacturer Part Number: VO4661-X007T - Package: SOIC-8 - License: https://creativecommons.org/licenses/by/4.0/ **Pins:** - A1 [pin 1] - A2 [pin 4] - C1 [pin 2] - C2 [pin 3] - GND [pin 5] - VCC [pin 8] - VO1 [pin 7] - VO2 [pin 6] ### J1 — [FTSH-103-01-L-D](https://www.flux.ai/adrian95/ftsh-103-01-l-d~6h8.md) - Role Details: SWD debug header intended as: pin 1 = target reference, pin 2 = SWDIO, pin 3 = NRST, pin 4 = GND, pin 5 = GND, pin 6 = SWO. Board also provides SWCLK on series-damped path for debugger access; verify final header silk/pin numbering during schematic cleanup. - Part Type: Connector - Manufacturer Name: Samtec - Manufacturer Part Number: FTSH-103-01-L-D - Datasheet URL: https://suddendocs.samtec.com/catalog_english/ftsh_th.pdf - Package: 2x3 1.27mm - License: https://creativecommons.org/licenses/by/4.0/ - Role: SWD Header **Pins:** - 01 [pin 01] - 02 [pin 02] - 03 [pin 03] - 04 [pin 04] - 05 [pin 05] - 06 [pin 06] ### J2 — [282837-2](https://www.flux.ai/vasy_skral/282837-2~69k.md) - Role: Terminal Block - Datasheet URL: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=282837&DocType=Customer+Drawing&DocLang=English - Role Details: Power input terminal: pin 1 = VIN_9_36V, pin 2 = GND. Accepts rugged 9-36V DC field supply. - Manufacturer Part Number: 282837-2 - Manufacturer Name: TE Connectivity AMP Connectors - Part Type: Connector - Package: 2-pin 5.08mm **Pins:** - 1 [pin 1] - 2 [pin 2] ### J3 — [282837-2](https://www.flux.ai/vasy_skral/282837-2~69k.md) - Datasheet URL: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=282837&DocType=Customer+Drawing&DocLang=English - Part Type: Connector - Role Details: Dry contact input terminal: pin 1 = DRY_IN_FIELD, pin 2 = GND return. - Role: Terminal Block - Manufacturer Name: TE Connectivity AMP Connectors - Manufacturer Part Number: 282837-2 - Package: 2-pin 5.08mm **Pins:** - 1 [pin 1] - 2 [pin 2] ### J4 — [282837-2](https://www.flux.ai/vasy_skral/282837-2~69k.md) - Role Details: Wet input terminal: pin 1 = WET_IN_FIELD (9-36V sense), pin 2 = GND return. - Role: Terminal Block - Package: 2-pin 5.08mm - Datasheet URL: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=282837&DocType=Customer+Drawing&DocLang=English - Manufacturer Name: TE Connectivity AMP Connectors - Manufacturer Part Number: 282837-2 - Part Type: Connector **Pins:** - 1 [pin 1] - 2 [pin 2] ### J5 — [282837-2](https://www.flux.ai/vasy_skral/282837-2~69k.md) - Part Type: Connector - Manufacturer Part Number: 282837-2 - Role Details: Pulse input terminal: pin 1 = PULSE_IN_FIELD (9-36V pulse sense), pin 2 = GND return. - Manufacturer Name: TE Connectivity AMP Connectors - Role: Terminal Block - Package: 2-pin 5.08mm - Datasheet URL: https://www.te.com/commerce/DocumentDelivery/DDEController?Action=srchrtrv&DocNm=282837&DocType=Customer+Drawing&DocLang=English **Pins:** - 1 [pin 1] - 2 [pin 2] ### J6 — [282837-4](https://www.flux.ai/adrian95/282837-4~o7p.md) - Manufacturer Name: TE Connectivity AMP Connectors - Role: Terminal Block - License: https://creativecommons.org/licenses/by/4.0/ - Package: 4-pin 5.08mm - Manufacturer Part Number: 282837-4 - Datasheet URL: https://www.te.com/usa-en/product-282837-4.datasheet.pdf - Role Details: Auxiliary field I/O terminal: pin 1 = GND, pin 2 = UART_FIELD_TX, pin 3 = UART_FIELD_RX, pin 4 = ANA_IN_FIELD (0-5V analog input). - Part Type: Connector **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] ### J7 — [282837-4](https://www.flux.ai/adrian95/282837-4~o7p.md) - Role: Terminal Block - Package: 4-pin 5.08mm - Manufacturer Part Number: 282837-4 - Datasheet URL: https://www.te.com/usa-en/product-282837-4.datasheet.pdf - Part Type: Connector - Role Details: Communications and output terminal: pin 1 = GND, pin 2 = RS485_A, pin 3 = RS485_B, pin 4 = OUT_SWITCHED_12V high-side output. - License: https://creativecommons.org/licenses/by/4.0/ - Manufacturer Name: TE Connectivity AMP Connectors **Pins:** - 1 [pin 1] - 2 [pin 2] - 3 [pin 3] - 4 [pin 4] ### LED1 — [0603GBD0790S01](https://www.flux.ai/adrian95/0603gbd0790s01~iak.md) - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/4336/0603GBD0790S01.pdf - Role Details: Panel/status indicator LED driven from 3.3V logic. - Package: 0603 - Part Type: LED - Manufacturer Part Number: 0603GBD0790S01 - Manufacturer Name: ORIENTAL TECHNOLOGY - Role: Status LED **Pins:** - A [pin 2] - K [pin 1] ### LED2 — [0603GBD0790S01](https://www.flux.ai/adrian95/0603gbd0790s01~iak.md) - License: https://creativecommons.org/licenses/by/4.0/ - Role: Status LED - Datasheet URL: https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/4336/0603GBD0790S01.pdf - Part Type: LED - Package: 0603 - Role Details: Panel/status indicator LED driven from 3.3V logic. - Manufacturer Part Number: 0603GBD0790S01 - Manufacturer Name: ORIENTAL TECHNOLOGY **Pins:** - A [pin 2] - K [pin 1] ### LED3 — [0603GBD0790S01](https://www.flux.ai/adrian95/0603gbd0790s01~iak.md) - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://mm.digikey.com/Volume0/opasdata/d220001/medias/docus/4336/0603GBD0790S01.pdf - Role Details: Panel/status indicator LED driven from 3.3V logic. - Part Type: LED - Package: 0603 - Manufacturer Part Number: 0603GBD0790S01 - Manufacturer Name: ORIENTAL TECHNOLOGY - Role: Status LED **Pins:** - A [pin 2] - K [pin 1] ### LED4 — [SML-LX0603GW-TR](https://www.flux.ai/adrian95/sml-lx0603gw-tr~uqi.md) - Datasheet URL: https://www.lumex.com/spec/SML-LX0603GW-TR.pdf - License: https://creativecommons.org/licenses/by/4.0/ - Part Type: LED - Package: 0603 - Manufacturer Name: Lumex Opto/Components Inc. - Manufacturer Part Number: SML-LX0603GW-TR - Role Details: Indicates MCU system heartbeat or board alive status. - Role: Status LED **Pins:** - A [pin 2] - K [pin 1] ### LED5 — [SML-LX0603GW-TR](https://www.flux.ai/adrian95/sml-lx0603gw-tr~uqi.md) - Manufacturer Part Number: SML-LX0603GW-TR - Role Details: Indicates communications activity or RS-485 status. - Manufacturer Name: Lumex Opto/Components Inc. - Package: 0603 - Role: Status LED - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://www.lumex.com/spec/SML-LX0603GW-TR.pdf - Part Type: LED **Pins:** - A [pin 2] - K [pin 1] ### LED6 — [SML-LX0603GW-TR](https://www.flux.ai/adrian95/sml-lx0603gw-tr~uqi.md) - Role Details: Indicates commanded 12V high-side output state. - License: https://creativecommons.org/licenses/by/4.0/ - Datasheet URL: https://www.lumex.com/spec/SML-LX0603GW-TR.pdf - Part Type: LED - Role: Status LED - Manufacturer Part Number: SML-LX0603GW-TR - Manufacturer Name: Lumex Opto/Components Inc. - Package: 0603 **Pins:** - A [pin 2] - K [pin 1] ### SW1 — [SWITCH-PUSH-6mm-H5mm-4pin](https://www.flux.ai/baronunread/switch-push-6mm-h5mm-4pin~4u.md) - Part Type: Switch - License: https://creativecommons.org/licenses/by/4.0/ - Package: 6mm THT - Role: Pushbutton - Role Details: Manual control switch used for MCU reset or BOOT0 recovery mode. **Pins:** - 1-1 [pin 1-1] - 1-2 [pin 1-2] - 2-1 [pin 2-1] - 2-2 [pin 2-2] ### SW2 — [SWITCH-PUSH-6mm-H5mm-4pin](https://www.flux.ai/baronunread/switch-push-6mm-h5mm-4pin~4u.md) - Role Details: Manual control switch used for MCU reset or BOOT0 recovery mode. - License: https://creativecommons.org/licenses/by/4.0/ - Role: Pushbutton - Part Type: Switch - Package: 6mm THT **Pins:** - 1-1 [pin 1-1] - 1-2 [pin 1-2] - 2-1 [pin 2-1] - 2-2 [pin 2-2] ### U1 — [STM32F103C8T6](https://www.flux.ai/jharwinbarrozo/stm32f103c8t6~qe2.md) - Manufacturer Part Number: STM32F103C8T6 - Implementation Details: Industrial controller MCU. Decouple each VDD pin with local 100nF. VDDA filtered from +3V3 through ferrite bead. BOOT0 held low with pull-down and pushbutton override. NRST filtered and driven by external watchdog. HSE 8MHz and optional LSE 32.768kHz fitted for timing/debug flexibility. - Package: LQFP-48 - Part Type: Microcontroller - Datasheet URL: https://datasheet.lcsc.com/lcsc/1811151642_STMicroelectronics-STM32F103C8T6_C8734.pdf - Role Details: Main application controller; handles dry, wet, pulse, and analog inputs, RS-485/UART communications, output control, status reporting, and watchdog refresh. - Role: MCU - Manufacturer Name: STMicroelectronics **Pins:** - BOOT0 [pin 44] - NRST [pin 7] - PA0_WKUP [pin 10] - PA1 [pin 11] - PA10 [pin 31] - PA11 [pin 32] - PA12 [pin 33] - PA13 [pin 34] - PA14 [pin 37] - PA15 [pin 38] - PA2 [pin 12] - PA3 [pin 13] - PA4 [pin 14] - PA5 [pin 15] - PA6 [pin 16] - PA7 [pin 17] - PA8 [pin 29] - PA9 [pin 30] - PB0 [pin 18] - PB1 [pin 19] - PB10 [pin 21] - PB11 [pin 22] - PB12 [pin 25] - PB13 [pin 26] - PB14 [pin 27] - PB15 [pin 28] - PB2 [pin 20] - PB3 [pin 39] - PB4 [pin 40] - PB5 [pin 41] - PB6 [pin 42] - PB7 [pin 43] - PB8 [pin 45] - PB9 [pin 46] - PC13_TAMPER_RTC [pin 2] - PC14_OSC32_IN [pin 3] - PC15_OSC32_OUT [pin 4] - PD0_OSC_IN [pin 5] - PD1_OSC_OUT [pin 6] - VBAT [pin 1] - VDD [pin 24] - VDD [pin 48] - VDD [pin 36] - VDDA [pin 9] - VSS [pin 23] - VSS [pin 47] - VSS [pin 35] - VSSA [pin 8] ### U2 — [LT3991EMSE-5#PBF](https://www.flux.ai/adrian95/lt3991emse-5pbf~6cj.md) - Implementation Details: Wide-input 5V buck stage from protected VIN. Use short high-current loop for VIN-SW-inductor-output path and place input/output capacitors close to pins. - Manufacturer Part Number: LT3991EMSE-5#PBF - Role: Buck Regulator - License: https://creativecommons.org/licenses/by/4.0/ - Package: MSOP-10 - Role Details: Primary power converter from protected VIN to 5V rail with industrial input headroom. - Part Type: Integrated Circuit - Datasheet URL: https://www.analog.com/media/en/technical-documentation/data-sheets/3991fa.pdf - Manufacturer Name: Analog Devices Inc. **Pins:** - BD [pin 1] - BOOST [pin 2] - EN [pin 5] - EPAD [pin 11] - PG [pin 9] - RT [pin 8] - SS [pin 7] - SW [pin 3] - SYNC [pin 10] - VIN [pin 4] - VOUT [pin 6] ### U3 — [THVD1451D](https://www.flux.ai/kicad-part-library/thvd1451d~z1b.md) - Role Details: Converts MCU UART to differential RS-485 bus with DE and RE direction control. - Datasheet URL: http://www.ti.com/lit/ds/symlink/thvd1451.pdf - Package or Case Code: SOIC-8_3.9x4.9mm_P1.27mm - Role: RS-485 Transceiver - Manufacturer Part Number: THVD1451D - Package: SOIC-8 - Manufacturer Name: Texas Instruments Inc. **Pins:** - A [pin 8] - B [pin 7] - D [pin 3] - GND [pin 4] - R [pin 2] - VCC [pin 1] - Y [pin 5] - Z [pin 6] ### U4 — [MAX6370](https://www.flux.ai/kicad-part-library/max6370~0tn.md) - Package or Case Code: SOT-23-8 - Manufacturer Name: Maxim Integrated Products, Inc. - Package: SOT-23-8 - Role: Watchdog Supervisor - Role Details: Monitors watchdog toggle from MCU and drives system reset on timeout. - Datasheet URL: https://datasheets.maximintegrated.com/en/ds/MAX6369-MAX6374.pdf - Manufacturer Part Number: MAX6370 **Pins:** - ~{WDO} [pin 7] - GND [pin 2] - NC [pin 3] - SET0 [pin 4] - SET1 [pin 5] - SET2 [pin 6] - VCC [pin 8] - WDI [pin 1] ### U5 — [AUIR33402S](https://www.flux.ai/kicad-part-library/auir33402s~70a.md) - Manufacturer Name: Infineon Technologies AG - Package: D2PAK - Datasheet URL: https://www.infineon.com/dgdl/auir33402s.pdf?fileId=5546d462533600a4015355a88074135c - Implementation Details: Protected semiconductor output stage for high-side 12V-class load switching. Requires thermal copper area and careful PCB current-path design for any high-current demonstration load. - Role Details: Protected semiconductor switch for rugged high-current field output with MCU control and fault monitoring. - Manufacturer Part Number: AUIR33402S - Package or Case Code: TO-263-7_TabPin4 - Role: High-Side Power Switch **Pins:** - Cb [pin 5] - GND [pin 3] - IFB [pin 1] - IN [pin 2] - OUT [pin 6] - OUT [pin 7] - VCC [pin 4] ### U6 — [MCP6001T-I-OT](https://www.flux.ai/jecstronic/mcp6001t-i-ot~s1u.md) - Part Type: Operational Amplifier (OP-AMP) - Package: SOT-23-5 - Role: Op Amp Buffer - Datasheet URL: https://ww1.microchip.com/downloads/en/DeviceDoc/MCP6001-1R-1U-2-4-1-MHz-Low-Power-Op-Amp-DS20001733L.pdf - Manufacturer Part Number: MCP6001T-I/OT - Role Details: Buffers and filters scaled analog input before ADC sampling. - Manufacturer Name: Microchip Technology **Pins:** - - [pin 4] - + [pin 3] - OUTPUT [pin 1] - V- [pin 2] - V+ [pin 5] ### X1 — [NX3225GD-8MHZ-STD-CRA-3](https://www.flux.ai/lcsc/nx3225gd-8mhz-std-cra-3~3n50.md) - Package: 3.2x2.5mm - Manufacturer Part Number: NX3225GD-8MHZ-STD-CRA-3 - JLCPCB Part Class: Extended Part - Role Details: Primary high-speed clock reference for STM32 timing and communications. - Frequency: 8MHz - Manufacturer Name: NDK - Operating Temperature: -40~+150℃ - Frequency Stability: 150ppm - LCSC Part Number: C889706 - Role: HSE Crystal - Load Capacitor: 8pF - Package or Case Code: OSC-SMD_2P-L3.2-W2.5 - Part Type: Crystals **Pins:** - 1 [pin 1] - GND [pin 2] ### X2 — [NX3215SA-32.768K-EXS00A-MU00003](https://www.flux.ai/jecstronic/nx3215sa-32p768k-exs00a-mu00003~26r.md) - Datasheet URL: https://media.digikey.com/pdf/Data%20Sheets/NDK%20PDFs/NX3215SA-32.768kHz-EXS00A-MU00003.pdf - Manufacturer Part Number: NX3215SA-32.768K-EXS00A-MU00003 - Manufacturer Name: NDK America, Inc. - License: https://creativecommons.org/licenses/by/4.0/ - Package: 3.2x1.5mm - Frequency: 32.768kHz - Part Type: Oscillator - Role: LSE Crystal - Role Details: Optional low-speed RTC timekeeping reference. **Pins:** - P1 [pin 1] - P2 [pin 2] *The full schematic, PCB layout, bill of materials, and interactive design are available at [https://www.flux.ai/samael33/industrial-embedded-io-controller-board~qd](https://www.flux.ai/samael33/industrial-embedded-io-controller-board~qd).* --- *Generated from [https://www.flux.ai/samael33/industrial-embedded-io-controller-board~qd](https://www.flux.ai/samael33/industrial-embedded-io-controller-board~qd)*