The aim of the payload we want to develop is twofold. First of is educative, we want to be able to produce a payload that can be placed inside SERA3 and that can work smoothly both during test phase and launch of the rocket. The second goal of this project is to measure the difference in the magnetic field of the Earth as the rocket gets further away from its surface. In this chapter we are going to explain the components of the payload and its technical and mechanical requirements.

Components

In this section we are introducing some of of the main elements we are going to use in the payload.

Arduino Uno

Arduino/Genuino Uno is a microcontroller board based on the ATmega328P. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz quartz crystal, a USB connection, a power jack, an ICSP header and a reset button.

We will use this board as the main board of the payload. We will connect to this microcontroller all the rest of the components we will need to do the aforementioned measurements. All the technical specifications of this board are detailed in table on a right.

For more information about the Arduino Uno schematics there is a whole electrical layout at https://www.arduino.cc/en/uploads/Main/Arduino_Uno_Rev3-schematic.pdf

arduino_uno

Microcontroller ATmega328P
Operating Voltage 5V
Input Voltage (recommended) 7-12V
Input Voltage (limit) 6-20V
Digital I/O Pins 14 (of which 6 provide PWM output)
PWM Digital I/O Pins 6
Analog Input Pins 6
DC Current per I/O Pin 20 mA
DC Current for 3.3V Pin 50 mA
Flash Memory 32 KB (ATmega328P)of which 0.5 KB used by bootloader
SRAM 2 KB (ATmega328P)
EEPROM 1 KB (ATmega328P)
Clock Speed 16 MHz
LED_BUILTIN 13
Dimentions 53.4 mm x 68.6 mm
Weight 25 g

Magnetometer

The chosen magnetometer for the payload has been the HMC5883L model. The HMC5883L is a surface-mount, multi-chip module designed for low-field magnetic sensing with a digital interface for applications such as lowcost compassing and magnetometry. It includes  high-resolution HMC118X series magneto resistive sensors plus an ASIC containing amplification, automatic degaussing strap drivers, offset cancellation, and a 12-bit ADC that enables 1° to 2° compass heading accuracy. The I2C serial bus allows for easy interface. The HMC5883L is a 3.0x3.0x0.9mm surface mount 16-pin leadless chip carrier (LCC).

Accelerometer

The chosen accelerometer for the payload has been the ADXL345 model. It is a small, thin, low power, 3-axis accelerometer with high resolution (13-bit) measurement at up to ±16 g. Digital output data is formatted as 16-bit twos complement and is accessible through either a SPI (3- or 4-wire) or I2C digital interface. It measures the static acceleration of gravity in tilt-sensing applications, as well as dynamic acceleration resulting from motion or shock. Its high resolution (4 mg/LSB) enables measurement of inclination changes less than 1.0°.

Gyroscope

The chosen gyroscope for the payload has been the ITG-3200 model. The ITG-3200 features three 16-bit analog-to-digital converters (ADCs) for digitizing the gyro outputs, a user-selectable internal low-pass filter bandwidth, and a Fast-Mode I2C (400kHz) interface. Additional features include an embedded temperature sensor and a 2% accurate internal oscillator.

The ITG-3200 can be powered at anywhere between 2.1 and 3.6V. For power supply flexibility, the ITG-3200 has a separate VLOGIC reference pin (labeled VIO), in addition to its analog supply pin (VDD) which sets the logic levels of its serial interface. The VLOGIC voltage may be anywhere from 1.71V min to VDD max. For general use, VLOGIC can be tied to VCC. The normal operating current of the sensor is just 6.5mA.

Image credits: CC-BY SparkFun Electronics from Boulder, USA