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Slamtec RPLIDAR A1 on an Alphabot with a Raspberry PI

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This project describes how to connect a Slamtech RPLIDAR A1 directly to a Raspberry PI by using its in-built serial port. So no need to use the supplied USB interface.

This repository contains a C++ class which reads the coordinates and also does the motor control via PWM of the RPI.

A 360 degree scan is provided by a callback at the sampling rate of the LIDAR which is kept at 300RPM (5Hz).

Wiring

There are two sockets on the LIDAR. One is for the serial communication and the other for the motor control. The serial data is transmitted via the Raspberry PI serial port and the speed is controlled with GPIO pin 18.

Use the cable which comes with the LIDAR and plug its two plugs into the two sockets on the LIDAR and chop off the single connector at the other end.

Solder the wires to the serial port of the Raspberry PI and port 18:

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The motor can be receiving the unregulated battery voltage (<10V) or the 5V from the raspberry PI but the serial interface requires 5V.

Rapberry PI config

  • Start raspi-config
  • Select Serial Port Enable/disable shell messages on the serial connection
  • Answer No: Would you like a login shell to be accessible over serial?
  • Answer Yes: Would you like the serial port hardware to be enabled?
  • Reboot when prompted

Software

Prerequisites

Install the pigpio package and development headers:

apt-get install libpigpio-dev

Installation

cmake .

make

sudo make install

This installs the library and can then be used in your application.

A1Lidar class

The class has start() and stop() functions which start and stop the data acquisition and also start and stop the motor of the range finder.

The data is transmitted via DataInterface where the abstract function newScanAvail(float rpm, A1LidarData (&)[A1Lidar::nDistance]) = 0 needs to be implemented which then receives both the polar and Cartesian coordinates after a successful 360 degree scan. Register your DataInterface with registerInterface.

Example program

printdata prints tab separated distance data as x <tab> y <tab> r <tab> phi <tab> strength until a key is pressed.

Pipe the data into a textfile and plot it with gnuplot:

sudo ./printdata > tt2.tsv
gnuplot> plot "tt2.tsv"

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printRPM prints the current RPM until you press ctrl-C.

Credits

The rplidarsdk folder is the sdk folder from the official Slamtec git (latest v1.x):

https://github.com/Slamtec/rplidar_sdk