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105 lines
3.9 KiB
105 lines
3.9 KiB
# Detect proximity - Raspberry Pi
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In this part of the lesson, you will add a proximity sensor to your Raspberry Pi, and read distance from it.
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## Hardware
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The Raspberry Pi needs a proximity sensor.
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The sensor you'll use is a [Grove Time of Flight distance sensor](https://www.seeedstudio.com/Grove-Time-of-Flight-Distance-Sensor-VL53L0X.html). This sensor uses a laser ranging module to detect distance. This sensor has a range of 10mm to 2000mm (1cm - 2m), and will report values in that range pretty accurately, with distances above 1000mm reported as 8109mm.
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The laser rangefinder is on the back of the sensor, the opposite side to the Grove socket.
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This is an I<sup>2</sup>C sensor.
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### Connect the time of flight sensor
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The Grove time of flight sensor can be connected to the Raspberry Pi.
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#### Task - connect the time of flight sensor
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Connect the time of flight sensor.
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1. Insert one end of a Grove cable into the socket on the time of flight sensor. It will only go in one way round.
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1. With the Raspberry Pi powered off, connect the other end of the Grove cable to one of the I<sup>2</sup>C sockets marked **I<sup>2</sup>C** on the Grove Base hat attached to the Pi. These sockets are on the bottom row, the opposite end to the GPI pins and next to the camera cable slot.
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## Program the time of flight sensor
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The Raspberry Pi can now be programmed to use the attached time of flight sensor.
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### Task - program the time of flight sensor
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Program the device.
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1. Power up the Pi and wait for it to boot.
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1. Open the `fruit-quality-detector` code in VS Code, either directly on the Pi, or connect via the Remote SSH extension.
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1. Install the rpi-vl53l0x Pip package, a Python package that interacts with a VL53L0X time-of-flight distance sensor. Install it using this pip command
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```sh
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pip install rpi-vl53l0x
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```
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1. Create a new file in this project called `distance-sensor.py`.
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> 💁 An easy way to simulate multiple IoT devices is to do each in a different Python file, then run them at the same time.
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1. Add the following code to this file:
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```python
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import time
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from grove.i2c import Bus
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from rpi_vl53l0x.vl53l0x import VL53L0X
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```
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This imports the Grove I<sup>2</sup>C bus library, and a sensor library for the core sensor hardware built into the Grove time of flight sensor.
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1. Below this, add the following code to access the sensor:
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```python
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distance_sensor = VL53L0X(bus = Bus().bus)
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distance_sensor.begin()
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```
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This code declares a distance sensor using the Grove I<sup>2</sup>C bus, then starts the sensor.
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1. Finally, add an infinite loop to read distances:
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```python
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while True:
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distance_sensor.wait_ready()
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print(f'Distance = {distance_sensor.get_distance()} mm')
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time.sleep(1)
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```
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This code waits for a value to be ready to read from the sensor, then prints it to the console.
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1. Run this code.
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> 💁 Don't forget this file is called `distance-sensor.py`! Make sure to run this via Python, not `app.py`.
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1. You will see distance measurements appear in the console. Position objects near the sensor and you will see the distance measurement:
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```output
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pi@raspberrypi:~/fruit-quality-detector $ python3 distance_sensor.py
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Distance = 29 mm
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Distance = 28 mm
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Distance = 30 mm
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Distance = 151 mm
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```
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The rangefinder is on the back of the sensor, so make sure you use the correct side when measuring distance.
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> 💁 You can find this code in the [code-proximity/pi](code-proximity/pi) folder.
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😀 Your proximity sensor program was a success!
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