This code reads data from an accelerometer and four VESCs, writes it to SD card, and transmits it to another machine for recording and visualisation.
This requires the ADXL372 module from https://github.com/mjg59/ADXL372
At startup, 4 serial ports are configured for communication with the VESCs. These ports are set to use inverted signalling, in order to cope with the opto-isolators in the circuit. A command is sent to each, corresponding to the VESC "Get Values" command.
Another serial port is configured for over the air communication. This is not connected via opto-isolators, and so does not need signals to be inverted. However, the buffer size for serial transmission is increased.
An analogue pin is configured with a PWM frequency of 10kHz and a duty cycle of 10% in order to generate a 10kHz timer signal for external synchronisation.
If an SD card is present, the set of existing files will be examined and the first available number between 0 and 4095 will be used as a filename. This will be used to log data locally for later retrieval.
Finally, an SPI-attached ADXL372 will be configured to provide accelerometer data.
Event handlers are registered for each VESC serial port. Upon a byte of data being received by the hardware, the handler will be called and the byte will be read into the corresponding VESC's buffer. The data is parsed to ensure that it is valid, and the expected length of the packet is extracted from the data provided by the VESC. Once the entire packet has been read, the corresponding VESC's local structure is updated to indicate that it is complete and a timestamp is set to show the time of completion. The data is then written out to SD card.
The main loop cycles through each VESC structure in turn, looking for ones that have complete data packets. If it finds more than one, it will pick the one that has the oldest data. It will then check whether the telemetry serial port is currently sending any data, by checking whether the buffer is empty. If it isn't, it will write the data. This will not block, since the hardware is capable of performing serial writeout in the background. If data is currently being written, the loop will continue.
If a VESC hasn't updated in over a second, the code will assume that something has gone wrong, reinitialise local state and send another query command.
If data was previously being written but the output serial buffer is now empty, the VESC whose data was being output is sent another query command in order to trigger a new data query.
The accelerometer, if present, will then also be read and the values compared to the last transmitted acceleration data. If greater than a threshold difference, the accelerometer data will be transmitted and written to SD card.
Finally, the loop will check whether the remote machine sent an enter byte three times in a row in under two seconds. If so, it will enter interactive mode. In this mode no live telemetry data is sent - instead, the user can send commands to list the files on the SD card, dump the contents of a file or wipe files from the SD card. This allows recovery of logged data without having to disassemble the board.
The radios use the SiK firmware. Modules need to be appropriately configured to communicate with each other. To program a controller, connect it (either directly via USB, or with a USB to serial adapter) and run
screen /dev/ttyUSB0 115200
If the controller hasn't yet been configured, you'll need to use 57600 instead of 115200 - try both if the first doesn't work. Wait a second after connecting, and then rapidly type
+++
and wait a second. An "OK" prompt will appear, and you are now in command mode. Type
ATI5
and hit enter to view the current configuration, which will look something like:
S0:FORMAT=25
S1:SERIAL_SPEED=115
S2:AIR_SPEED=250
S3:NETID=25
S4:TXPOWER=20
S5:ECC=1
S6:MAVLINK=1
S7:OPPRESEND=1
S8:MIN_FREQ=915000
S9:MAX_FREQ=928000
S10:NUM_CHANNELS=50
S11:DUTY_CYCLE=100
S12:LBT_RSSI=0
S13:MANCHESTER=0
S14:RTSCTS=0
S15:MAX_WINDOW=131
Parameters are set by typing
ATSn=value
where n refers to the number in the ATI5 output. For example, to set serial_speed to 115:
ATS1=115
The important values are:
- serial_speed - set to 115 (115,200 bps). This is what the software assumes.
- air_speed - set to 250. If greater range is required, reduce this - valid values are 2, 4, 8, 16, 19, 24, 32, 48, 64, 96, 128, 192 and 250. Reducing this value will reduce available bandwidth, so only do so if necessary.
- netid - this pairs a transmitter with a receiver, and must be the same for both.
- ecc - set this to 1 to enable error checking and correction. This results in the actual bit rate available being half of air_speed (hence why air_speed is set to a larger value than serial_speed)
- num_channels - set to 50
- lbt_rssi - set to 0
- max_window - set to 131
But basically, make sure they all match. Once these values are programmed, save them:
AT&W
and reboot the radio
ATZ
Note that radios with different firmware versions may not be able to speak to each other even if all other values are set correctly! You can view the firmware version by running:
ATI
Alternatively, configuration can be performed with Mission Planner. This will also let you update firmware.