TOF1 Time of Flight

J2 carries the 5 V supply input and the CAN bus. The mating connector is the Phoenix Contact 1027605. The 5 V input is regulated to 2.8 V on the board, which powers the microcontroller, the sensor and the CAN transceiver logic supply.

Fitting a jumper on JP1 connects a 120 Ω termination resistor across the CAN bus. Fit it only on the two nodes at the ends of the bus. Jumper pitch: 1 mm.

J1 is designed for use with the ST-LINK-V3MINIE and can be used to debug the board or load firmware onto the microcontroller. The debugger must work at the 2.8 V logic level of the board (pin 3). The SWO and virtual COM port pins are not connected. Mating part: 14-pin STDC14 Cortex ribbon cable.

J3 is an 8-pin header (1.27 mm pitch) with four rows. Each row has a signal pin (odd pin numbers 1, 3, 5, 7) beside a ground pin (even pin numbers 2, 4, 6, 8). Every signal pin has a 10 kΩ pull-up to 2.8 V, so an open row reads 0 and a jumper fitted across a row pulls its signal low, which sets that bit to 1. The four rows form a 4-bit value (0 to 15), with row 1 as the least significant bit, and the node ID is 32 plus this value. Each fitted jumper draws 0.28 mA (2.8 V through 10 kΩ). The board silkscreen numbers the rows 1 to 4.

J3 pinout and function

Example J3 settings (1 = jumper fitted) and the resulting node ID

Every node on a DroneCAN bus has a unique node ID from 1 to 127, which is the source address of the messages it sends. The TOF1 uses a static node ID that is chosen as follows. If a node ID has been stored in flash over CAN (see below), that ID is used as is. Otherwise the node ID is 32 plus the value set with the jumpers on J3, giving IDs 32 to 47; with no jumpers fitted the ID is 32. The jumpers are read at start-up only, so reset or power-cycle the board after changing one. Give each board on the same bus its own node ID, and keep it different from the flight controller’s own node ID. The sensor_id field of the range message is set to the node ID.

To store an ID over CAN, use the standard DroneCAN parameter services (for example in the DroneCAN GUI tool, or tools/can_param.py from the firmware repository): write the integer parameter NODE_ID (1 to 127) with uavcan.protocol.param.GetSet. The stored ID overrides the J3 jumpers and is used after the node restarts, which can be requested with uavcan.protocol.RestartNode. Writing 0 removes the stored ID so that the J3 jumpers are used again. The ID can also be stored while programming with tools/flash_and_check.py --set-node-id. Writing flash stops the processor for a few tens of milliseconds, so do not change the ID while the sensor is in use.

The board publishes uavcan.equipment.range_sensor.Measurement (type ID 1050) at the measurement rate, 10 Hz by default. The table lists the fields exactly as defined in the DroneCAN DSDL [4]; the last column shows the value this board writes.

uavcan.equipment.range_sensor.Measurement (DTID 1050)

reading_type values

Four integer parameters can be read and written over CAN with uavcan.protocol.param.GetSet (for example from the DroneCAN GUI tool or tools/can_param.py). They are stored in flash and kept across restarts: the node ID in the flash page at 0x0801F000 (page 62), the distance mode in the page at 0x0801E800 (page 61) and the measurement period in the page at 0x0801F800 (page 63). An erased page means the default.

The beam orientation is sent in the beam_orientation_in_body_frame field as a DroneCAN coarse orientation: roll, pitch and yaw in multiples of 15° (90° is 6). The default, a beam pointing down, is pitch -90°. PX4 turns this into the distance sensor rotation (downward, upward, or horizontal in 45° steps of yaw); other angles it treats as a custom rotation.

The sensor timing budget is derived from the measurement period: it is the largest of 20, 33, 50, 100 and 200 ms that is no more than 80% of the period, so the default period of 100 ms uses a 50 ms budget. The headroom is needed: with the budget equal to the period the sensor gave a failed reading between valid ones. A longer budget gives a longer range and better repeatability, but needs a longer period, so the maximum range in the specifications table is reached only with the long distance mode and a slow measurement rate (a 200 ms budget needs a period of 250 ms).

In automatic mode (DIST_MODE 3) the firmware chooses the distance mode. It starts in long mode and changes to short mode after three readings in a row that are a valid distance below 900 mm, below the sensor’s minimum range, or unusable; it returns to long mode after three readings in a row that are out of range or unusable, or a valid distance above 1200 mm. The thresholds are 300 mm apart, changes are at least one second apart, and the first reading after a change is not sent. The mode in use is reported in the sub-mode field of NodeStatus (1 = short, 2 = long). The choice is kept in RAM, so a restart begins in long mode.

The board reports the state of the sensor in the health field of NodeStatus. If the VL53L1CB does not answer on the I²C bus, the health is ERROR; if the sensor answers but delivers no measurement for 3 seconds, the health is WARNING. The vendor-specific status code tells the two apart.

PX4 uses the TOF1 as a range finder through its uavcan driver. Set the following parameters (a reboot is needed after changing them). The parameter names and defaults are from the PX4 parameter reference [3].

Connect an ST-LINK-V3MINIE to J1 (STDC14) to load firmware or debug over SWD. The repository’s tools/flash_and_check.py programs the board and then checks over CAN that the node answers GetNodeInfo. The node ID, distance mode, measurement period and beam orientation stored in flash can be set and cleared with the tools below.

The firmware repository includes Python scripts for use with a serial USB-CAN adapter (a ‘USB-CAN analyzer’ at 2 Mbaud, set to 1 Mbit/s CAN). Any DroneCAN GUI tool can also read and set the parameters.

For example, can_param.py 32 set BEAM_ORIENT up changes the beam orientation reported by node 32 (the words down, up, forward, right, back and left, or a number from 1 to 10, are accepted), and can_param.py 32 set DIST_MODE auto selects automatic distance mode. Changes to DIST_MODE, MEAS_PERIOD_MS and BEAM_ORIENT take effect at once and are kept in flash; a new NODE_ID is used after the node restarts. The orientation in use is also carried in every range message, and can_range_live.py shows it.