For BY70-1, an open telecommand is designed to allow radio amateurs to send commands to take and download an image. This article provides some details about it.
payload_mode-B7: Status for open telecommand. Set to 1 when enable.
payload_mode-B6: Status for camera task. Set to 1 when running.
payload_mode-B5: Status for valid image data. Set to 1 when valid.
payload_mode-B4: Status for camera power. Set to 1 when powered on.
cam_ham_en: Configuration for open command. 0x5A to enable.
cam_ham_interval: Minimum possible time between two commands in minutes.
A GNU Radio OOT module, gr-lilacsat is necessary for telemetry and image receiving. It can be downloaded here: https://github.com/bg2bhc/gr-lilacsat/
Radio Parameters for Open Telecommand
Frequency: 145.920 MHz
Date Rate: 1000 bps
Protocol: AX.25 UI
The open telecommand shares the same uplink channel with FM repeater. No PL required.
The 1000 bps FSK-FM is simply a frequency domain scaled version of common used 1200 bps AFSK. The mark and space frequencies are 1000 Hz and 1833.33 Hz.
A single byte command should be used in the data field. Samples in .wav format are also provided.
– 0x00: Take an image and send it via RF. http://lilacsat.hit.edu.cn/wp-content/uploads/2017/01/open_cam_cmd_00.wav
– 0x55: Take an image and store it in the memory. http://lilacsat.hit.edu.cn/wp-content/uploads/2017/01/open_cam_cmd_55.wav
– 0xAA: Read data from the memory and send it via RF. http://lilacsat.hit.edu.cn/wp-content/uploads/2017/01/open_cam_cmd_aa.wav
You can also use AFSK1200 TX block included in gr-lilacsat to generate these commands.
From our experience, command 0x55 and 0xAA are recommended.
To take an image:
– Check if payload_mode-B7 is set to 1.
– Send command 0x55. payload_mode-B4 and payload_mode-B6 will be set to 1 and payload_mode-B5 will be set to 0.
– Wait until payload_mode-B4 and payload_mode-B6 are set to 0 and payload_mode-B5 is set to 1.
To download an image:
– Check if payload_mode-B7 and payload_mode-B5 are set to 1.
– Send command 0xAA. payload_mode-B6 will be set to 1. The transmitter will start to send the data.
– Wait until the transmitter to stop. payload_mode-B6 will be set to 0.
For successful receiving, you may have to download several times. Some cooperation between amateurs, e.g. receive at the same time and keep an IQ record, may also be helpful.
After continuous running for a period, the system may have some difficult to create a task. A reset will recover it.