Solar Ecology

SID & ASE Electronics

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Written by Paulo Soares and Fermin Carranza-Cid

Systems Overview

The SID and ASE radiometric systems are controlled by a Broadcom BCM2835 microprocessor, integrated to a Raspberry Pi model Zero W computer. The Raspberry Pi computer works similar to a desktop computer; it runs a Linux-based Operational System (Raspbian or Raspberry PI OS), and most of the configuration required for the systems to work can be done via the OS command prompt. The radiometric systems described in this document use Raspbian version 8 (Jessie) or above. The computer counts with two USB ports, one mini-HDMI port, one slot for a camera, one MicroSD slot, and 40 GPIO pins that are used to connect sensors and other required devices to the computer. To work, the computer requires the OS to be flashed to the MicroSD card, which, in turn, also serves as the storage device for the solar irradiance data recorded by the system. 

Raspberry PI model Zero W. Source: Reddit

The systems are also composed of an Adafruit Industries DS3231 precision real-time clock (RTC) board, used to keep track of the time even in the absence of an internet connection. The DS3231 was chosen because this RTC uses a 32kHz timing crystal combined with a temperature sensor for correcting drifts caused by the change in temperature, turning the time-keeping of this board precise enough to be used in data logging applications. The DS3231 talks to the computer through an I2C bus (one of the computer’s GPIO pins). The Raspberry Pi computer has no native analog port, and analog to digital converter (ADC) was added to the system, allowing the computer to understand the signal from the solar irradiance sensors (pyranometers). We opted for using the Adafruit Industries ADS1115 16-bit ADC due to its precision and the possibility to program the gain amplification of the signal. The ADS1115 has four analog ports and communicates with the computer through the I2C bus. 

Adafruit ADS1115 analogic to digital (ADC) converter

The temperature measurements are recorded from two DS18b20 digital temperature sensors. The DS18b20 sensor is a digital programmable temperature sensor which works through the 1-wire interface. The temperature sensors were programmed to have a 12-bit response. One of the DS18b20 is a waterproof sensor used to retrieve measurements of the ambient air temperature, while the second DS18b20 is used to keep track of the temperature inside of the data logger. Solar irradiance is measured by silicon-based, in our case the LUNA PDB-C139 photodiodes. The photodiodes have a spectral range from 400 nm to 1100nm, coinciding with most of the shortwave radiation captured by solar photovoltaic systems, and a response time of 50ns, making this sensor highly sensitive to changes in the solar irradiance. 

The systems are also composed of two status LEDs: one used to indicate when the data logger is powered and the second is programmed to flash every time data is recorded. Data can be retrieved from the systems by using one of the computer’s USB port, or remotely, provided that an internet connection is available. The SID and ASE systems are programmed to sample data from the sensors every second; the samples are subsequently averaged to the minute and stored into the MicroSD card, which has 10 GB of memory allocated for data logging purposes (we opted to use 16 GB Sandisk memory cards, allocating 6GB for the OS, and the remaining for loggeing data), which should enable the systems to store approximately 20 years of data without running out of memory.

All of these components were soldered onto a designed printed circuit board (PCB). This circuit board permits all of our electrical components to connect and communicate with each other. 

 

The SID System

A complete list of the required electronic components to assemble SID system is: 

  • Raspberry Pi Zero - x1
  • Adafruit DS3231 – Precision Real Time Clock (RTC) - x1
  • DS 18B20 Temperature Sensors - x2
  • LUNA PDB-C139 Photodiodes - x2 
  • ADS1115 - Analog to Digital Converter (ADC) - x1
  • 5MM LED’s - green and yellow - x2
  • 4.7 k-ohm Resistors for the temperature sensors - x2
  • 470 Ohm Resistors for the photodiodes - x2
  • 330 ohm resistor for the LEDs - x2
  • Printed Circuit Board - x1

 

The ASE System

A complete list of the required electronic components to assemble ASE system is: 

  • Raspberry Pi Zero - x1
  • Adafruit DS3231 – Precision Real Time Clock (RTC) - x1
  • DS 18B20 Temperature Sensors - x2
  • LUNA PDB-C139 Photodiodes - x5 
  • ADS1115 - Analog to Digital Converter (ADC)-  x2
  • 5MM LED’s - green and yellow - x2
  • 4.7 k-ohm Resistors for the temperature sensors - x2
  • 470 Ohm Resistors for the photodiodes - x5
  • 330 ohm resistor for the LEDs-  x2
  • Printed Circuit Board - x1

 

We suggest:

  • EasyEDA - a website for designing printed circuit boards for free.
  • JLCPCB - manufacturer website for printing the printed circuit boards.