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Using Electronic Modules with Jim Rowe Quason VL6180X - Laser rangefinder - Light level sensor This module should be of particular interest if you want to build robotic devices. It uses infrared (IR) light to accurately sense the proximity of objects from 0mm to well over 100mm. It’s based on a technology known as FlightSense, patented by ST Microelectronics. T he Quason VL6180X range-­ sensing module comes on a tiny 17.8 × 20.3mm PCB with a handful of SMD components on it. As you can see from the photos, it includes three SOT23-3 devices and one 12-lead SMD IC, itself only 4.8 × 2.8 × 1mm. The secret is all inside that innocent-­ looking 12-lead IC in the centre of the PCB. There’s a lot more in that tiny package than you might expect. It’s a complete optical ranging system with a tiny IR (infrared) laser, two optical sensors (one for IR, the other for ambient light sensing), plus a microcontroller unit (MCU) with internal memory. This IC is the heart of the VL6180X sensing module – the rest of the components are there just to support it. Inside the VL6180X The IR laser driver section is shown in the centre, with the range detection section just above the MCU. To make a ranging measurement, the MCU first sends a command pulse to the IR laser driver to send out a short IR light pulse at a wavelength of 850nm. Then, it measures the time until the ranging detection section reports that a reflected IR pulse has been received. The MCU can then calculate the current distance to the object that reflected the IR pulse, by taking into account the speed of light in air and the time taken for the out-and-back journey. The speed of light in air is close to 299,702,458m/s (metres per second), which equates to 299.702m per microsecond or 0.2997m per nanosecond. Fig.1: the block diagram for the VL6180X rangefinder IC. The internals appear quite simple, with a separate section for the light sensing, IR emitter and ranging. However, very precise timing is required to make calculations down to the millimetre resolution, so the actual circuitry is more complicated than you might think. It’s made by European semiconductor manufacturer ST Microelectronics and uses its patented FlightSense technology. Unlike optical sensors that attempt to detect distance by measuring the proportion of light sent to an object that is reflected back from it, ST’s technology accurately measures the time the light takes to travel to the nearest object and reflect back to its sensor, which ST calls the ‘time of flight’. In short, it’s a kind of light-based radar or ‘LIDAR’. Fig.1 shows what’s inside the VL6180X and should help in understanding how it works. Near the bottom is the MCU with its ROM (readonly memory) and RAM (random-­ access memory) below it, while above it is the ambient light sensing section. siliconchip.com.au So light takes close to 3.336ns to travel one metre or 0.3336ns to travel 100mm. If the out-and-back journey of the light takes, say, 0.6672ns, the total path length is 200mm, so the distance between the sensor and the object must be 100mm. The key to this method of determining distance is precise measurements of very short time delays. To measure over a range of 1-100mm with 1mm resolution, the chip must have a timer capable of measuring the difference between emission and reception from just 7ps (picoseconds) to 667ps with 7ps resolution or better. One picosecond is one trillionth (10−12) of a second! Such capability is thanks to modern semiconductor manufacturing Australia's electronics magazine July 2023  31 Here the module is shown at nearly three times actual size for clarity. techniques that can make tiny transistors with predictable properties. In addition to this ‘time of flight’ range measurement, the VL6180X can also measure the ambient light level using the sensor and ambient light sensing (ALS) section shown at the top of Fig.1. This appears to be a ‘bonus’ feature as it does not factor into the distance measurements It can measure light levels between 0.002 lux and 20,971 lux, with what is described as a ‘photopic’ response. That means it responds to light wavelengths in the visible range of 400700nm (with a peak at around 550nm) as seen by the human eye at ‘well-lit’ lighting levels. The MCU in the VL6180X can take these measurements either once or repetitively and can also interleave range and ALS measurements. It accepts commands and makes the measurement data available via the Fig.2: the top of the VL6180X IC features three tiny holes that are critical for its functionality. These apertures are required for sensing and emission, with the largest being only 0.58mm in diameter. There is also an even smaller ‘vent’ hole. It’s important to note that the light sensor has a very narrow ‘cone’ and measures objects up to 150-200mm away. 32 Silicon Chip I2C port (pins 5 and 6) at lower right in Fig.1. You are probably wondering how all these impressive things can be done by the very small and innocent-­looking chip visible in the centre of the module PCB. Although they are not easy to see with the naked eye, there are actually three apertures on the top of the device, located on its centre line as shown in Fig.2 (which shows the top of the VL6180X at six times its actual size). The largest aperture (0.58mm diameter) near the centre is for the ALS sensor, while the smaller 0.5mm diameter one near the far end is for the IR ranging laser emissions. The even smaller 0.3mm diameter aperture near the ALS at the pin 1 end is for the IR ranging return sensor. A fourth and very tiny ‘vent’ hole is at lower centre, midway between pins 3 and 4. The VL6180X is designed to operate from a supply of 2.8V ±0.2V, with an average operating current of 1.7mA in ranging mode or 300µA in ALS mode. The current it draws in standby mode is less than 1µA. And the I2C interface can operate at up to 400kHz, with a 7-bit address of 0x29 (41 decimal). The full module Fig.3 shows the complete circuit of the Quason module, with the all-­ important VL6180X device (IC1) visible at lower left. At top centre is REG1, an XC6206 LDO voltage regulator used to step down the 5V input supply (at pin 7 of CON1) to the 2.8V needed by IC1. The 2.8V from REG1 is also made Useful links • www.aliexpress.com • www.st.com/content/st_com/ en.html • www.arduinolibraries.info/ libraries/vl6180-x • github.com/adafruit/Adafruit_ VL6180X available at pin 6 of CON1, for possible use by external circuitry. Both the GPIO0 and GPIO1 pins of IC1 are pulled up to 2.8V via 47kW resistors. The GPIO1 pin is then taken directly to pin 4 of CON1, while the GPIO0 pin is connected to pin 3 of CON1 via diode D1. This allows IC1 to be held in standby mode by pulling pin 3 of CON1 to ground. That is why this pin of CON1 is labelled “SHDN” (for “shutdown”). Mosfets Q1 and Q2, connected between the SCL and SDA pins of IC1 and the corresponding pins 2 and 1 of CON1, provide logic-level conversion. This way, the 2.8V signal swings at pins 5 and 6 of IC1 are converted into 5V swings at pins 2 and 1 of CON1, and vice versa. This allows the module to be connected to external circuitry running from a 5V supply, like an Arduino or similar MCU. The way this kind of ‘passive’ level shifter works is quite clever. Q1 & Q2 are N-channel devices, so they switch on when their gate voltage (“G”) is significantly higher than the source voltage (“S”). At idle, the source is pulled to +2.8V via one 10kW resistor, while the drain is pulled to +5V via another. Fig.3: the circuit diagram for the Quason module which utilises the VL6180X IC. Q1 and Q2 are used for logic-level conversion. Australia's electronics magazine siliconchip.com.au With the gate and source both at +2.8V, the Mosfet is off, so no current flows. If IC1 pulls its end low, the gatesource voltage becomes +2.8V, so the Mosfet switches on and the corresponding pin on CON1 also goes low. Alternatively, if the pin on CON1 is externally pulled low (eg, by an MCU), the Mosfet is initially off. Still, its parasitic ‘body diode’ (visible in Fig.3) allows the corresponding pin on IC1 to be pulled down to about +0.7V. The gate-source voltage of that Mosfet is then 2.8V − 0.7V = 2.1V, high enough for the Mosfet to switch on, pulling the pin on IC1 down to 0V. So when one side goes low, the other does too, but if both sides are allowed to be pulled high by the pull-up resistors, they remain high at different voltage levels. Fig.4: the Quason module can be easily connected to an Arduino Uno (or similar), with just four leads. Connecting it to an Arduino As you can see from Fig.4, connecting the module to an Arduino Uno or compatible is very straightforward. The module’s VIN pin connects to the Arduino’s 5V pin, its GND pin connects to one of the Arduino’s GND pins, and its SCL and SDA pins connect to the same pins on the Arduino. You will also need an Arduino library to get the two communicating, plus a sketch to use the library to make measurements. A couple of these libraries are listed on the Arduino website at www.arduinolibraries. info/libraries/vl6180-x – in both cases, they provide links to the library ZIP files on GitHub. When you download and unzip either of these libraries, they generously provide example sketches to get you going. I downloaded one of these libraries, added it to my list of libraries in the Arduino IDE and then loaded one of its example sketches. It was only a few minutes before I could wave my hand up and down above the VL6180X and see its As you can see from this enlarged photo, the Quason VL6180X is miniature, measuring just 17.8 x 20.3mm. siliconchip.com.au Australia's electronics magazine distance varying in the ranging data on the Arduino IDE’s Serial Monitor. It was as simple as that! So it’s pleasingly easy to get the Quason VL6180X IR range sensing module going with an Arduino. This, plus its low cost, suggests that it would be very suitable for DIY robotics. You might even be able to use a couple of the modules to make a digital Theremin! Where to get it We obtained the module in the photos from the Quason Official Store, one of the vendors on AliExpress (see www.aliexpress.com/ item/1005001572022389.html), for $4 including shipping. But there are several other vendors on AliExpress offering it for similar prices, such as SuperModule Store, DIY-Victor Store and HARYE Store. It is also available from eBay supplier Cakemol8 for just over $10, including shipping. And Australian firm AHEM Engineering (https://shop. ahem.net.au) also seems to have it for $12.45 (including GST) plus postage cost. A very similar VL6180X-based module can be found on the website of Newcastle firm Core Electronics (https://core-electronics.com.au) for $23.15 + $6.00 for shipping. While it is considerably more expensive than the AliExpress and eBay sellers, you are likely to get it within a couple of days rather than a few weeks due to being shipped from Australia. SC July 2023  33