VL53L8CH Motion Indicator doesn’t work correctly with 8x8 resolution

[KKKK9]

I’m using the VL53L8CH sensor with an ESP32 and developing a program in Arduino language based on Example_10_motion_indicator.c provided by ST. I successfully obtained the motion indicator output using a 4x4 map.

Next, I tried switching to an 8x8 map by applying the following settings:

VL53L8CH sensor(&Wire, LPn_PIN);

sensor.set_resolution(VL53LMZ_RESOLUTION_8X8);
sensor.motion_indicator_init(&motion_config, VL53LMZ_RESOLUTION_8X8);

However, when I checked the output, I noticed that the 1st and 2nd values, as well as the 9th and 10th values, are identical, resulting in behavior similar to a 4x4 map.

Could you please advise if there are any additional settings required or if this might be related to a library issue? Any suggestions or insights would be greatly appreciated.

[Anne BIGOT]

Hello

The reason for this is....
- The size of the Motion Indicator structure is 32 elements. This is determined by VL53L8CH firmware.
- For reference see the line "uint32_t per_aggregate_indicator_1[VL53LMZ_MI_INDICATOR_LENGTH];" in the file vl53lmz_plugin_motion_indicator.h
- Since we can't have 64 outputs from Motion Indicator we chose to reduce down from 64 to 16 to keep a regular 2x2 reduction.
- This is why in Motion Indicator mode the mi__agg_id array is mapping 64 zones to just 16 motion indicator output elements.
- Code in vl53lmz_motion_indicator_set_resolution() creates this map from 64 zones to 16 outputs.
- It is possible to use all 32 possible outputs with small changes in the vl53lmz_plugin_motion_indicator.c file. Doing this you could, for instance, have a mapping from 2x1 zones to Motion Indicator outputs
- In fact the mi__agg_id map allows a completely flexible mapping from zones to motion_indicator outputs.

Best regards