System at a Glance

EquiSat’s electronics were designed to accomplish the following tasks:

  • Supply a reliable means for operating and communicating with the radio.
  • Drive four high-power LEDs.
  • Handle data from our sensors and convert it into signals our processor can read.
  • Charge our batteries and convert voltages to allow our systems to operate.
  • Electrically ground the chassis.
  • Implement all power and radio transmission inhibits.
  • Contain low-power and Commercial Off-The-Shelf (COTS) parts.

Overview

At the core of our electronics is our ATMEL microprocessor; we are using a SAMD21J18A. It will generate all control signals, read in all signals, send all data to the radio, and make all decisions as to charging, LED flashing, and operational modes. You can learn more about our processor and its interaction with our Radiation-Safe Memory, MRAM (Magnetoresistive RAM), on the Avionics Software page.

There are three main signal paths in our satellite.

  • Power:  from our solar panels to all ICs (Integrated Circuits) and LEDs
    • Our five solar panels contain 120 solar cells that convert light to electricity.
    • We use Max Power Point Tracking (MPPT) ICs to optimize battery charging from solar cells and protect our batteries from damage.
    • Our batteries are inhibited from being connected to their loads by two kill switches: one on a flash panel and one in the rail of the chassis.
    • We have three voltage regulators that convert our batteries’ voltages to voltages that our other systems need.
    • Our driver board contains 4 Boost Regulators that convert 6.6V and 60A from our batteries, to 36V and 3A for our LEDs
  • Control: signals for demultiplexing and turning on other hardware
    • Our processor controls: LED flashing, antenna deployment, radio transmission enable, battery charge enables, and radio power enable.
    • Demultiplexing allows us to have 18 sensors and multiple sense voltages read on one analog input pin, our processor controls this with 8 control signals.
  • Data: signals, both analog and digital, containing information from our sensors and between our MRAM, radio, and processor.
    • We use I2C, SPI, and JTAG to communicate serially with various sensors, MRAM, and our programmer respectively
    • Our battery charge information is digital, we record the times when those signals change
    • All of our other sensors and signals are analog, and are demultiplexed to be read on one processor pin.

EquiSat’s PCBs

  • Flash Panel:  houses our 4 LEDs, our antenna deployment mechanism, 5 temperature sensors, an IR sensor, and a photodiode.
  • LED Driver Board: home to our 4 boost regulator circuits, each that draw 60A at 6.6V from out batteries and convert it into 36V and 2.7A to drive our LEDs; it also contains 2 temperature sensors and the drive circuitry for our antenna deployment mechanism.
  • Battery Board: sandwiched between our batteries, this board contains circuitry to perform Max Power Point Tracking (MPPT), which optimizes battery charging based on current solar panel outputs, and charge our batteries.
  • Control Board: the brain of the satellite, this board contains our processor and memory, as well as de-multiplexers to handle all of our data from all of the other boards. This board also interfaces with the radio and umbilical connection, and contains a temperature sensor and a magnetometer.
  • Radio Adapter Board: this is a simple board that provides a connector interface between our radio and the control board.
Carlos ('16) soldering the Control Board
Carlos ('16) soldering the Control Board

About

EquiSat’s electronics are designed, tested, and, with the exception of PCB manufacturing, assembled completely in house. In keeping with EquiSat’s mission, all parts are COTS and easily purchased from any online supplier. Additionally, everything was designed with simplicity and low cost in mind to help increase reproducibility. Checkout the resources page for more about our Avionics. We use CADSOFT’s EAGLE  software to design our schematics and layout our PCBs. We use GitHub for keeping all of our files synced between all of our members, our repo can be found below: