P19104: HABIP-BioX
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Communication System Preliminary Detailed Design

Table of Contents

Communication System Preliminary Detailed Design

Communication System Feasibility: Prototyping, Analysis

Power Analysis and Block Diagram

Calculations were done to determine the amount of power that is needed to support all the functionality that the communication system would need to support. It was calculated that:

The Video system draws a maximum of~14W of power while transmitting.

The 2m transceiver draws 11W in Tx mode, 3.1W in Rx mode, and 0.6W of power in standyby mode.

The rest of the communication system that will be housed on a custom PCB consumes a maximum of 1.7W of power.

Power Usage Scenarios

Power Block Diagram

Power Block Diagram

Data Block Diagram

The below image shows how data and signals will be sent within the comm board and to the other boards in the entire system.

Communication Board Data Block Diagram

Communication Board Data Block Diagram

Raspberry Pi Pin out

The below image shows how the Raspberry Pi pinout will be set up to deliver the required data communication and signaling to the communication board as well as the other PCBs in the system.

Pi 0 Connections

Pi 0 Connections

2m Transceiver Block Diagram

The same implementation for the 2m Transceiver that was done originally two years ago by MSD team P17104 will be used again. The implementation goes as follows:

The Raspberry Pi will be running an open source software called MiniModem, in two separate threads. One thread will handle receiving data from the Baofeng Radio; the other will handle transmitting data to the Baofeng Radio.

Minimodem uses FSK (Frequency Shift Keying) to modulate and demodulate digital data as audio, and vice versa. A USB sound card will be used to transmit and receive this data as audio.

With audio going out in both directions between the Baofeng radio and the USB sound card, through the audio out/mic in ports of each device, a bidirectional communication link is developed. Any digital data that needs to reach the Raspberry Pi in the HAB from the base station will be modulated into audio at Mission Control using MiniModem, and transmitted over 2m. The Baofeng radio will then receive this audio, and output it to the Raspberry Pi. The audio will be demodulated to digital data on the Raspberry Pi, using MiniModem in conjunction with the USB sound card.

If the Raspberry Pi wishes to reply with data, it must only use MiniModem to modulate this data into Audio over the sound card. The Raspberry Pi zero will at the same time pull the Push to Talk (PTT) line of the Baofeng radio low using a GPIO and BJT, causing the transceiver to go into Tx mode. In this state, all data send through the audio input to the transceiver will be transmitted over the 2m band, where it can be received by the base station.

A loop-back test with MiniModem running on a Raspberry Pi was done in the past with the USB sound card at 1200 bps. It fully worked which is why this solution will be reused, possibly with new parts.

A block diagram showing this implementation is shown below:

RPI0 to Baofeng Connection Diagram

RPI0 to Baofeng Connection Diagram

A website that gets more into this method of using Raspberry Pi's along with a data transceiver is listed below:

https://www.marcelpost.com/wiki/index.php/GPIO_pin_on_the_RPi_to_trigger_PTT

RF Connection Diagram

The below image shows the RF connections that will be between the 2m transceiver and the 2m antenna. This connection scheme is the same as was used previously in HABIP senior designs.

RF Connection Diagram

RF Connection Diagram

Ground Commands

This section includes preliminary lists of commands that will be sent to the platform as well as the commands sent from the communication system to the rest of the system. Ground commands will be received from the ground by the communication subsystem. The communication subsystem will then send certain commands to the rest of the system to acquire needed information to be sent down to the ground station.

Preliminary List of Commands to Payload

Preliminary List of Commands from Communication System to Rest of Payload

Commands to request data:

Command actions

Communication System Schematics

Power Management Schematic sheet

Power Management Schematic sheet

Power Mangagement Schematic sheet

Power Mangagement Schematic sheet

Power Connector Schematic sheet 1

Power Connector Schematic sheet 1

Temperature and Pressure Sensor Schematic sheet

Temperature and Pressure Sensor Schematic sheet

GPS&WDT Schematic sheet

GPS&WDT Schematic sheet

Data Connector Schematic sheet

Data Connector Schematic sheet

Data Connector Schematic sheet

Data Connector Schematic sheet

2m Connector Schematic sheet

2m Connector Schematic sheet

A link to a pdf of all the slides of the schematic can is here:

Preliminary Detailed Design Documents/Comms/Schematics/Comms_schematics.pdf

Communication System Bill of Material (BOM)

A high level BOM that contains most of the main parts of the system that will be purchased is listed below.

Communication System BOM

Communication System BOM

A link to this sheet, and all the other BOMs from in the project can be found here: (Communication BOM is on "Communication System BOM" sheet)

Preliminary Detailed Design Documents/Master_BOM.xlsx

Communication System Budget

Communication System Budget

Communication System Part Cost Breakdown

Communication System Part Cost Breakdown

Communication System Test Plans

Test Plans related to the communication subsystem that will verify that the engineering requirements are satisfied are listed below:

ER2: Commands decoded and executed at over 100m

Commands will be sent between the payload and the base station with a distance between them of at least 100m. This test can be conducted with the payload on the ground with the commands being one that can most easily be determined to have been executed. Commands that were received and executed and those that were not will be recorded. This will not be done in the 1 week lab test.

ER4: APRS Transmission Rate

The APRS will be set up to transmit commands at the desired rate. The APRS will be powered using 5V or 3.3V. The APRS will then start transmitting AX.25 APRS packets. The packets will be received by either the 2m receiving equipment in use or the general APRS network that will upload the results to the APRS network that is visible using the aprs.fi website on any computer that has internet access. This will be done during the lab test.

ER33: Telemetry Range

APRS

During a 3 hour flight the transmission range of the APRS will be tested so that at any point of its flight where it is within 50 miles of a APRS receiver, the APRS packet shall be received. This is to be tested separately on the ground by driving in a car up to 50 miles away. The APRS location shall be view able using the APRS.fi website, and there shall be no point where the APRS cannot be received.

Sensor Data

During a flight, the data sent via the 2m transceiver that is successfully received at the base station will be compared against the relative altitude of the balloon using the pressure sensor on the communication board. During a ground test, a powered payload will be driven around so that the distance between the payload and 2m receiver at the base station will extend to 50 miles. The telemetered data shall be received at all times during the car ride(assuming line of sight).

ER34: Telemetry Data Rate

Data pertaining to the biocell such as photos, sensor data as well as platform sensor data and photos shall be telemeterd to a receiver to satisfy the data rate stated. The amount of data sent over a fixed period of time will be used to calculate the average amount of bits sent per second.

A link to the excel document that contains all of the test plans can be found here: Preliminary Detailed Design Documents/Test_Plan_w_ERs.xlsx



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