Solar Tracker Using BPW34S Photodiodes

Overview

This project demonstrates how to create a highly accurate solar tracking system using an array of photodiodes, operational amplifiers, a precision voltage reference, a temperature sensor, and an ESP32-based IoT platform. The setup involves:

1. BPW34S Photodiodes for sensing light intensity.
2. OPA2300AIDGST Operational Amplifiers for amplifying photodiode signals.
3. LT6650CS5 Precision Voltage Reference to bias the photodiodes.
4. STS35 Temperature Sensor for temperature compensation.
5. Olimex ESP32-POE2 for processing and transmitting data over Ethernet via Power over Ethernet (PoE).

This solar tracker can determine the sun's position in real time by analyzing the intensity of light captured by the photodiodes and compensating for temperature variations.

 

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Components

1. Photodiodes (BPW34S):
   • High-sensitivity silicon photodiodes.
   • Arranged in four rows of two phot

diodes each, connected in parallel to amplify their output signals.

2. Operational Amplifiers (OPA2300AIDGST):

   • Dual-channel op-amps used for precision amplification.
   • One op-amp handles the two photodiodes connected in parallel, providing a single output for each direction: UP, DOWN, LEFT, and RIGHT.

3. LT6650CS5 Precision Voltage Reference:

   • Provides a stable 0.4V reference voltage to bias the photodiodes via 500Ω resistors.
   • Ensures consistent performance across varying light and environmental conditions.

4. STS35 Temperature Sensor:

   • High-accuracy temperature sensor connected via I2C.
   • Used to monitor temperature and compensate for variations that may affect photodiode sensitivity.

5. Olimex ESP32-POE2:

   • ESP32-WROVER-E-based board with PoE support.
   • Handles signal processing from the photodiodes and temperature sensor.
   • Sends the data to a network for analysis or further usage.

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Circuit Description

1. Photodiode Biasing:

   • Each BPW34S photodiode is reverse-biased at 0.4V using the LT6650CS5 reference voltage.
   • Biasing is achieved through a 500Ω resistor for each photodiode, ensuring optimal linearity in the photocurrent-to-irradiance response.

2. Signal Amplification:

   • The signals from the photodiodes are fed into the OPA2300AIDGST op-amps.
   • Each op-amp output represents the light intensity from one direction: UP, DOWN, LEFT, or RIGHT.

3. Temperature Compensation:

   • The STS35 sensor provides real-time temperature readings to account for temperature-dependent variations in photodiode performance.

4. Analog Signal Processing:

   • The outputs from the op-amps (representing light intensities) are connected to the ADC inputs of the ESP32-WROVER-E-N4R8 module on the Olimex ESP32-POE2 board.

5. Data Transmission:

   • The ESP32-PoE2 transmits the processed light intensity and temperature data over Ethernet via PoE to a network for real-time monitoring and solar tracking analysis.

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Software Implementation

1. ESP32 Firmware:

   • ADC Configuration: Reads analog signals from the photodiode arrays and converts them to digital values.
   • I2C Interface: Communicates with the STS35 sensor to read temperature data.
   • Data Processing: Combines light intensity and temperature data, applies compensation algorithms, and determines the sun's position.
   • Networking: Uses PoE to send the processed data to a server or cloud platform for visualization and control.

2. Data Visualization:

   • The ESP32 sends data to a server application where a dashboard can display:
     • Light intensities from all four directions.
     • Calculated sun position.
     • Real-time temperature for diagnostics.

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Assembly and Connections

1. Photodiodes:

   • Connect the cathodes of the BPW34S photodiodes to the LT6650 output through 500Ω resistors.
   • Anodes are connected to the ground.

2. OPA2300AIDGST:

   • Configure the op-amps in a non-inverting configuration.
   • Feed the photodiode outputs into the op-amp inputs.

3. STS35:

   • Connect to the ESP32-PoE2 via the I2C interface (SCL and SDA).

4. ESP32-PoE2:

   • Connect the op-amp outputs to the ESP32 ADC inputs.
   • Power the board and sensors through PoE from a compatible Ethernet switch.

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Applications

1. Solar Tracking:

2. Environmental Monitoring:

3. IoT Integration:

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Advantages of the System

1. High Accuracy: Precision components ensure reliable solar position detection.
2. Temperature Compensation: STS35 improves the accuracy by accounting for environmental variations.
3. IoT Connectivity: PoE-based ESP32 enables seamless data transmission to networks.
4. Scalability: Easily adaptable for larger solar tracking systems or other environmental monitoring applications.

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With this setup, you can achieve precise solar tracking and integrate the data into your IoT ecosystem for advanced solar energy management.

 

For step file for assembly click here.

For PCB and schematic files in KiCAD click here.