Communication System Preliminary Detailed Design
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
- A maximum of 27 Watts of power is needed to transmit DTV, transmitt 2m at maximum power and to run all other functions of the communication system.
- A maximum of 13 Watts of power is needed to transmit 2m at maximum power and to run all other functions of the communication system.
- A maximum of 4.8 Watts of power is needed to continuously receive on the 2m band, and run all other functions of the communication system.
- A maximum of 2.2 Watts of power is needed to have the 2m transceiver on standby, and run all other functions of the communication system.
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.
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.
2m Transceiver Block DiagramThe 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:
A website that gets more into this method of using Raspberry Pi's along with a data transceiver is listed below:
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.
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
- Transmit Image
- Change camera/lighting for image(IR, RGB light)
- Change APRS transmission interval
- Change data transmission interval/rate
- Change data transmission power
- Command to turn the reaction wheel on/off
- Command to tell the reaction wheel to turn by a certain amount of degrees
- Cut down balloon
- Change Power mode
Preliminary List of Commands from Communication System to Rest of Payload
Commands to request data:
- Request temperature from various other boards
- Request photo with certain parameters
- Request pressure/altitude.
- Request IMU data from the DACQ
- Start all sensor logging
- Time sync for logging
- Command Biocell to change type of picture being taken
- Process status request
- Command heading for reaction wheel if add compass; if not, give it amount of degrees to turn
- Command to turn reaction wheel on/off
Communication System Schematics
A link to a pdf of all the slides of the schematic can is here:
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.
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)
Communication System Test PlansTest 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
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.
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