Tutorial: STMicroelectronics VL6180X Time-of-Flight LIDAR Sensor

For many of my applications I need to measure a distance. I have used ultrasonic sensors, but there view angle (beam) is not able to detect smaller objects, it very much depends on the object surface and angle, it is slow and not very precise. I have used infrared sensors, but here again it depends on the infrared reflection of the object in range, it depends the amount of reflected light is not really telling much about the distance, and yet IR reflection is subject of material and object targeted.

But there is yet another sensor type to consider: ToF! ToF (or Time-of-Flight) sensors have a built-in LIDAR: The sensor is sending out light pulses and measures how much time it takes for the light to come back. Similar to ultrasonic sensors (see “Tutorial: Ultrasonic Ranging with the Freedom Board“), but instead of ultrasonic it uses an infrared laser light. Or think about a radar system using an infrared laser light.

Vl6180x Breakout Board with tinyK20 (NXP Kinetis K20) Microcontroller-board

VL6180X

STMicroelectronics calls its technology ‘FlightSense’. It uses a SPAD (Single Photon Avalanche Diode) array and a VCSEL (Vertical Cavity Surface-Emitting Laser), combined with an ALS (Ambient Light Sensor) on the VL6180x. The ToF technology starts to be used in more and more applications: from gesture recognition, human presence detection in public transportation up to detect and measure object distances (e.g. how far a mobile phone is from the ear to adopt the audio volume).

The STMicroelectronics VL6180X sensor is a very small one. Its LGA package makes it a bit difficult to solder it, at least with my SMD soldering skills (my students are by far better!). That’s why breakout modules from Pololu , Sparkfun or Adafruit are a good starting point. Additionally the VL6180X device is operating at 2.8V: the breakout modules include the necessary voltage generator and level shifter to use the module in 3.3V or 5V systems. The sensor uses IR light at 850 nm and the VL6180X comes with an extra ALS (Ambient Light Sensor):

VL6180X Close View

The sensor is specified for ranging up to 10 cm with a resolution of 1 mm, but I have found it works fine with the default settings and good conditions up to about 20 cm. There range scaling factor which can be used:

1: ranging up to 20 cm, 1 mm resolution
2: ranging up to 40 cm, 2 mm resolution
3: ranging up to 60 cm, 3 mm resolution

The range scaling is not mentioned in the data sheet, but mentioned in UM1876.

Wiring

Below a picture of the Pololu breakout module:

Remove the I2C pull-ups if using multiple sensor boards on the same bus, or if the I2C bus already has pull-ups attached.

Vl6180x Breakout Board Top Side

The board has the following pins (left-to-right in the picture below):

GPIO1: programmable interrupt output
GPIO0/CE: driving this pin low puts the sensor into standby, otherwise it can be used as programmable interrupt output of the sensor. The CE function is needed if multiple sensors are on the same I2C bus (more about this later)
SCL: I2C clock
SDA: I2C data
GND: Ground
VIN: supply voltage (2.7-5V)
VDD: 2.8V regulator output

VL6180X Breakout Board Bottom Side

Wiring

Using a single sensor, only SCL, SDA, GND and VIN are needed. Below is how I have wired it up with a tinyK20 microcontroller board:

VL6180X Wiring

I2C Interface

To read and write the device registers over I²C, I’m using the following routines with the GenericI2C (GI2C1) driver:

uint8_t VL_WriteReg8(uint8_t i2cDeviceAddress, uint16_t reg, uint8_t val) {

uint8_t r[2];

r[0] = reg>>8;

r[1] = reg&0xff;

return GI2C1_WriteAddress(i2cDeviceAddress, &r[0], sizeof(r), &val, sizeof(val));

}

uint8_t VL_WriteReg16(uint8_t i2cDeviceAddress, uint16_t reg, uint16_t val) {

uint8_t r[2], v[2];

r[0] = reg>>8;

r[1] = reg&0xff;

v[0] = val>>8;

v[1] = val&0xff;

return GI2C1_WriteAddress(i2cDeviceAddress, &r[0], sizeof(r), &v[0], sizeof(v));

}

uint8_t VL_ReadReg8(uint8_t i2cDeviceAddress, uint16_t reg, uint8_t *valP) {

uint8_t tmp[2];

tmp[0] = reg>>8;

tmp[1] = reg&0xff;

return GI2C1_ReadAddress(i2cDeviceAddress, &tmp[0], sizeof(tmp), valP, 1);

}

uint8_t VL_ReadReg16(uint8_t i2cDeviceAddress, uint16_t reg, uint16_t *valP) {

uint8_t tmp[2];

tmp[0] = reg>>8;

tmp[1] = reg&0xff;

return GI2C1_ReadAddress(i2cDeviceAddress, &tmp[0], sizeof(tmp), (uint8_t*)valP, 2);

}

Sensor Initialization

The sensors need a special initialization sequence, explained in AN4545 and DT0037:

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/* Initialize sensor with settings from ST application note AN4545, section 9 -

"Mandatory : private registers" */

uint8_t VL_InitDevice(uint8_t i2cDeviceAddress) {

uint8_t res;

res = VL_WriteReg8(i2cDeviceAddress, 0x207, 0x01);

if (res!=ERR_OK) {