# Tuya Inline Chemical Sensor POC

## Description

Proof\-of\-concept long narrow Tuya Wi\-Fi interface board for a 4\-wire chemical sensor using MODBUS\-RTU over RS\-485\. Powered from external Class 2 12 VAC, with sensor DC power output, one power LED, and one Wi\-Fi pairing/reset button\.

## Project Details

- **Owner:** illuminex2026
- **Created:** 9/10/2026
- **Last Updated:** 10/16/2026
- **Visibility:** Public
- **Implementation Details:** CBU module, 3\.3 V buck, half\-duplex MODBUS\-RTU, four\-wire sensor with rectified DC output
- **Connectivity:** Wi\-Fi and RS\-485
- **Power Requirements:** External Class 2 AC
- **Human Interface:** LED and Button
- **Domain:** Industrial Sensor Interface
- **Compliance:** Class 2
- **Software:** Tuya
- **Operating Voltage:** 12VAC

## Key Components

### BR1 — [HD01\-T](https://flux.ai/adrian95/hd01-t.md)

- License: https://creativecommons\.org/licenses/by/4\.0/
- Functional Group: AC Input / Protection / Rectification
- Mount: Surface Mount
- Manufacturer Name: Diodes
- Part Type: Diodes
- Package or Case Code: 4\-SMD
- Datasheet URL: https://www\.diodes\.com/datasheet/download/HD01\.pdf
- Role: Bridge Rectifier
- Manufacturer Part Number: HD01\-T
- Role Details: 1 A, 100 V full\-wave bridge; \>2\.8x expected 0\.35 A AC source current

**Pins:**
- \- [pin 3]
- \+ [pin 1]
- \~\_1 [pin 2]
- \~\_2 [pin 4]

### D1 — [SMAJ24CA\-TP](https://flux.ai/lcsc/smaj24ca-tp~hngf.md)

- Part Type: TVS
- Manufacturer Part Number: SMAJ24CA\-TP
- Role Details: Bidirectional 24 V standoff TVS across fused 12 VAC input; avoids conduction at 14\.5 Vrms high\-line/no\-load while clamping surges
- Datasheet URL: https://storage\.googleapis\.com/graviton\-electric\-symbols/document\_assets/lcsc/2304140030\_MCC\-Micro\-Commercial\-Components\-SMAJ24CA\-TP\_C669029\.pdf
- Package or Case Code: SMA\_L4\.4\-W2\.6\-LS5\.0\-BI
- JLCPCB Part Class: Extended Part
- LCSC Part Number: C669029
- Manufacturer Name: MCC\(美微科\)
- Functional Group: AC Input / Protection / Rectification
- Product Info Url: https://lcsc\.com/product\-detail/TVS\_MCC\-Micro\-Commercial\-Components\-MCC\-SMAJ24CA\-TP\_C669029\.html
- Role: Protection

**Pins:**
- 1 [pin 1]
- 2 [pin 2]

### D2 — [SMBJ24A](https://flux.ai/cherepanyadima/smbj24a~2b.md)

- Datasheet URL: https://services\.taiwansemi\.com/storage/resources/datasheet/SMBJ%20SERIES\_R2104\.pdf
- Role Details: 24 V standoff TVS across protected rectified DC bus
- Functional Group: AC Input / Protection / Rectification
- Role: DC Surge Protection
- Manufacturer Name: Taiwan Semiconductor Corporation
- Manufacturer Part Number: SMBJ24A\-TR
- Part Type: TVS

**Pins:**
- A [pin 2]
- K [pin 1]

### D3 — [SM712\-02HTG](https://flux.ai/adrian95/sm712-02htg~cby.md)

- Mount: Surface Mount
- Part Type: Diodes
- Role: RS\-485 Surge Protection
- Manufacturer Part Number: SM712\-02HTG
- Role Details: SM712 asymmetric TVS array at outdoor probe connector
- Functional Group: RS\-485 / Protection / Termination
- License: https://creativecommons\.org/licenses/by/4\.0/
- Package or Case Code: SOT\-23
- Datasheet URL: https://www\.littelfuse\.com/media?resourcetype=datasheets&itemid=a4019802\-ff62\-41ff\-bf66\-295f97422f81&filename=littelfuse\-tvs\-diode\-array\-sm712\-datasheet
- Manufacturer Name: Littelfuse

**Pins:**
- 1 [pin 1]
- 2 [pin 2]
- 3 [pin 3]

### F1 — [1812L110/24DR](https://flux.ai/jecstronic/1812l11024dr~oz3.md)

- Part Type: Fuse
- Manufacturer Part Number: 1812L110/24DR
- Role Details: Littelfuse 1812L110/24DR, 24 V, 1\.10 A hold / 1\.95 A trip; 0\.73 A hold at 60 C versus 0\.49 Arms conservative source estimate; cURus/TUV
- Manufacturer Name: Littelfuse Inc\.
- Role: Protection
- Functional Group: AC Input / Protection / Rectification
- Datasheet URL: https://www\.littelfuse\.com/\~/media/electronics/datasheets/resettable\_ptcs/littelfuse\_ptc\_1812l\_datasheet\.pdf\.pdf
- Current Rating: 1\.1A
- License: https://creativecommons\.org/licenses/by/4\.0/

**Pins:**
- P1 [pin 1]
- P2 [pin 2]

### LED1 — [SML\-D13FWT86C](https://flux.ai/jecstronic/sml-d13fwt86c~i2q.md)

- License: https://creativecommons\.org/licenses/by/4\.0/
- Role: Power Indicator
- Manufacturer Name: Rohm Semiconductor
- Functional Group: Tuya Module / UI
- Manufacturer Part Number: SML\-D13FWT86C
- Part Type: LED
- Role Details: Single green 3\.3 V power LED
- Datasheet URL: https://fscdn\.rohm\.com/en/products/databook/datasheet/opto/led/chip\_mono/sml\-d13fwt86\(c\)\-e\.pdf

**Pins:**
- A [pin 2]
- K [pin 1]

### SW1 — [B3U\-1000P](https://flux.ai/adrian95/b3u-1000p~kb2.md)

- Functional Group: Tuya Module / UI
- License: https://creativecommons\.org/licenses/by/4\.0/
- Role: Pairing Button
- Role Details: Momentary active\-low Tuya pairing/reset input
- Manufacturer Part Number: B3U\-1000P
- Datasheet URL: https://omronfs\.omron\.com/en\_US/ecb/products/pdf/en\-b3u\.pdf
- Part Type: Switch
- Manufacturer Name: Omron Electronics Inc\-EMC Div

**Pins:**
- 1 [pin 1]
- 2 [pin 2]

### U1 — [LMR33630BDDAR](https://flux.ai/lcsc/lmr33630bddar~o51d.md)

- JLCPCB Part Class: Extended Part
- Manufacturer Part Number: LMR33630BDDAR
- Functional Group: 3\.3 V Buck
- Manufacturer Name: TI\(德州仪器\)
- LCSC Part Number: C544370
- Part Type: DC\-DC Converters
- Package or Case Code: SOIC\-8\_L4\.9\-W3\.9\-P1\.27\-LS6\.0\-BL\-EP2\.8\-1
- Role Details: LMR33630 36 V input, 3 A synchronous buck; R1/R2=100k/43\.2k sets 3\.315 V nominal\. Updated T1\-U rail bound 519\.4 mA; 600 mA design allowance\. PCB/thermal and Wi\-Fi transient verification deferred\.
- Datasheet URL: https://www\.ti\.com/lit/ds/symlink/lmr33630\.pdf
- Role: Buck Regulator

**Pins:**
- BOOT [pin 7]
- EN [pin 3]
- EP [pin 9]
- FB [pin 5]
- PG [pin 4]
- PGND [pin 1]
- SW [pin 8]
- VCC [pin 6]
- VIN [pin 2]

### U3 — [MAX3485ESA\+](https://flux.ai/lcsc/max3485esaplus~baoy.md)

- Part Type: Integrated Circuit
- Role: Logic\-level Shifting
- Role Details: MAX3485ESA\+ 3\.3 V half\-duplex RS\-485 transceiver; TX1 to DI, RO to RX1, P24 controls DE and active\-low RE
- JLCPCB Part Class: Extended Part
- Manufacturer Part Number: MAX3485ESA\+
- LCSC Part Number: C1545222
- Package or Case Code: SO\-8\_L4\.9\-W3\.9\-P1\.27\-LS6\.0\-BL
- Functional Group: RS\-485 / Protection / Termination
- Datasheet URL: https://www\.analog\.com/media/en/technical\-documentation/data\-sheets/max3483\-max3491\.pdf
- Symbol Style: parametric\-v1
- Manufacturer Name: MAXIM\(美信\)

**Pins:**
- \~\{RE\} [pin 2]
- A [pin 6]
- B [pin 7]
- DE [pin 3]
- DI [pin 4]
- GND [pin 5]
- RO [pin 1]
- VCC [pin 8]

*The full schematic, PCB layout, bill of materials, and interactive design are available at [https://flux\.ai/illuminex2026/tuya\-inline\-chemical\-sensor\-poc](https://flux.ai/illuminex2026/tuya-inline-chemical-sensor-poc).*

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*Generated from [https://flux\.ai/illuminex2026/tuya\-inline\-chemical\-sensor\-poc](https://flux.ai/illuminex2026/tuya-inline-chemical-sensor-poc)*