Low-Power Temp/Humidity Sensor Node

flux

  • Connected U1:+5V, U2:VCC, U3:VDD, LCD1:VDD, R1:P1, C1:P1, C2:P1 to ^5V
  • Connected U1:GND, U2:GND, U3:VSS, LCD1:VSS, LCD1:R/W, LCD1:LED(-), U3:A0, U3:A1, U3:A2, C1:P2, C2:P2, LCD1:VO to ^GND
  • Connected U1:D18/SDA, U3:SDA to ^SDA
  • Connected U1:D19/SCL, U3:SCL to ^SCL
  • Connected U1:D2, U2:DATA, R1:P2 to ^DHT_DATA
  • Connected U3:P0, LCD1:RS to ^LCD_RS
  • Connected U3:P1, LCD1:E to ^LCD_E
  • Connected U3:P4, LCD1:D4 to ^LCD_D4
  • Connected U3:P5, LCD1:D5 to ^LCD_D5
  • Connected U3:P6, LCD1:D6 to ^LCD_D6
  • Connected U3:P7, LCD1:D7 to ^LCD_D7
nets {
net 5V = U1:+5V, C2:P1, C1:P1, R1:P1, LCD1:VDD, U3:VDD, U2:VCC;
net GND = U1:6, GND:GND, U3 A2 - C1 P2:GND, LCD1:VO, C2:P2, C1:P2, U3:A2, U3:A1, U3:A0, LCD1:LED(-), LCD1:R/W, LCD1:VSS, U3:VSS, U2:GND;
net SDA = U1:D18/SDA, U3:SDA;
net SCL = U1:D19/SCL, U3:SCL;
net DHT_DATA = U1:D2, R1:P2, U2:DATA;
net LCD_RS = U3:P0, LCD1:RS;
net LCD_E = U3:P1, LCD1:E;
net LCD_D4 = U3:P4, LCD1:D4;
net LCD_D5 = U3:P5, LCD1:D5;
net LCD_D6 = U3:P6, LCD1:D6;
net LCD_D7 = U3:P7, LCD1:D7;
}

Task completed.

0:32

Checking 6 design areas.
Reading schematic details for U1, U2, U3 and 4 more.

flux

Work done
  • Renamed the project and updated its description to match the approved Arduino temperature-indicator design.
  • Created and populated the Project Specification with the architecture and implementation notes.
  • Added U1, U2, U3, LCD1, R1, C1, and C2.
  • Wired 5 V and GND to the sensor, LCD interface, and support parts.
  • Connected Arduino I2C to the LCD interface: U1 SDA/SCL -> U3 SDA/SCL.
  • Connected DHT22 data: U2 DATA -> U1 D2 with R1 as a 10k pull-up to 5 V.
  • Added 100 nF decoupling with C1 and C2 across the 5 V rail.
  • Mapped the LCD in 4-bit mode through U3: P0->RS, P1->E, P4->D4, P5->D5, P6->D6, P7->D7.
Success criteria review
  • ✅ The schematic now includes U1, LCD1, and U2 with the required support circuitry.
  • ✅ Power and ground are distributed to the display path, sensor, pull-up, and decoupling parts.
  • ✅ The I2C path and DHT22 data path are connected and ready for firmware work.
  • ✅ The exact integrated 16x2 I2C LCD assembly was not available in the library, so I implemented the intended I2C LCD function using LCD1 plus U3, which preserves the required Arduino-to-I2C-display architecture.
Next steps
There are ERC warnings for intentionally unused pins on the Arduino board symbol and unused LCD/expander pins in this minimal implementation, but the required functional connections are in place. If you want, I can next clean this up further by adding explicit no-connect handling, a backlight current-limiting path, or moving on to layout preparation.
Use D2 for DHT22
Add decoupling caps
Choose standard I2C pins
Add power connector
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Files

Schematic

Layout

3D View

Project Specification
Scope
Temperature indicator using an Arduino Uno, a 16x2 LCD display controlled over an I2C interface, and a DHT22 temperature and humidity sensor.
Architecture
Diagram



  
    
  
  
    
  








Digital data

5V and GND

Display drive

5V and GND





Arduino Uno R3
DHT22 Sensor
I2C LCD Interface
16x2 LCD
Decoupling and Pullup
Functional Requirements
  • Arduino Uno provides the 5 V rail and main controller logic.
  • DHT22 connects with VCC, GND, and a single digital DATA line.
  • DATA line includes a 10k pull-up to 5 V.
  • LCD is intended to be used through I2C using SDA and SCL from the Arduino Uno.
  • Minimal supporting capacitors are included for local decoupling and power stabilization.
Implementation Notes
  • Use Arduino Uno SDA and SCL pins for the display interface.
  • Use one Arduino digital GPIO for the DHT22 DATA signal.
  • Establish a common 5 V and GND network across all components.
  • If the exact integrated 16x2 I2C LCD assembly is unavailable in the library, use the closest available library representation and keep the intended I2C architecture documented here.
Design Summary
Status: Draft / Review / Approved
Manufacturing target: Prototype / EVT / DVT / PVT / Production
Software / firmware: repository link
Scope
Purpose
In scope
Out of scope
System context
Requirements
Functional
Electrical
Mechanical / environmental
Key constraints
Dependencies and risks
Dependencies
Key risks
Validation
Success criteria
Planned checks
Release-facing notes
Expected deliverables
Special release notes
Change notes / open questions
Changes in this revision
Open questions

  • Scope

  • Architecture

  • Functional Requirements

  • Implementation Notes

  • Design Summary

  • Scope

  • System context

  • Requirements

  • Functional

  • Electrical

  • Mechanical / environmental

  • Key constraints

  • Dependencies and risks

  • Validation

  • Release-facing notes

  • Change notes / open questions