The Documentation can be found here
With this API you can control your LEGO EV3 connected with USB from your Linux PC. Its main purpose is to provide a fast interface for controlling the LEGO EV3.
The LEGO EV3 will create a HID file in /dev/. You can access this with the HIDRAW API by the Linux Kernal. Lego has developed its own Protokoll. Some of it is explained in the EV3 Communication Developer Kit which can be downloaded here. Definitions for commands and other protokoll related things can be downloaded from the original EV3 sourcecode. The availible byte codes can be seen here as well as the details for the communication.
To run this without sudo use
KERNEL=="hidraw*", SUBSYSTEM=="hidraw", MODE="0664", GROUP="plugdev"
and place it in /etc/udev/rules/99-hidraw-permissions.rules.
Its needed to access the hidraw interface.
The library provides the an easy interface with Brick.h. Just link the library and start like:
#include "Brick.h"
int main(void)
{
Brick brick();
// initialize
if (!brick.Initialize())
return 1;
// read sensor val
int val = brick.getSensorVal(Input::Port1);
// set power to +99%
brick.setMotorPower(Output::A, 99);
// stop motor
brick.setMotorPower(Output::A, 0);
return 0;
}
If you want to handle the communication yourself you can use the class Command to create the an arbitrary command and send it with the HIDCon class.
This would look like here:
// message counter should increment each message
int msg_cnt = 0;
// There are direct commands and system commands. Both can and can not have a reply
Command c1(DIRECT_COMMAND_REPLY, msg_cnt++);
addOpCode(opINPUT_DEVICE);
addParameter((uint8_t)GET_RAW);
addParameter((uint8_t)0);
addParameter(port);
// the return value will be stored in the global var
addGlobalVar(0); // global var with index 0
// If the command has a reply it will be stored in binary here.
CBuffer reply;
con.Send(com.toBytes(),&reply)
// With this method you have to decode it yourself.
// Depending on the size, the global variables will be on the reply starting with byte 5
return reply[5];
Dependencys: git, cmake, make, c++ compiler (e.g. g++), python3-dev
git clone --recursive https://gitlab.gwdg.de/m.schlueter01/lego-raspi-api.git
mkdir build && cd build
cmake .. && make
The library is called legoapi.cpython-[...].so. Copy this in your execution folder call in python
The python interface implements is oriented at the pybricks API. It implements a subset of the Motor class.
import time
import legoapi
ma = legoapi.Motor(legoapi.Output.A)
mb = legoapi.Motor(legoapi.Output.B)
print("1")
ma.run(80)
mb.run(80)
time.sleep(2)
print("2")
ma.run(0)
mb.brake()
time.sleep(2)
print("3")
ma.run_time(80,1500,legoapi.Then.Brake)
mb.run_time(80,1000,legoapi.Then.Brake)
time.sleep(3)
print("4")
ma.run_time(80,1500,legoapi.Then.Coast)
mb.run_time(80,1500,legoapi.Then.Brake)
time.sleep(3)
print("5")
ma.run_angle(80,1500,legoapi.Then.Brake)
mb.run_angle(80,1000,legoapi.Then.Brake)
time.sleep(3)
print("6")
ma.run_angle(80,1500,legoapi.Then.Coast)
mb.run_angle(80,1500,legoapi.Then.Brake)
time.sleep(3)
print("7")
print("Motor A angle: {}".format(ma.angle()))
print("Motor B angle: {}".format(mb.angle()))
ma.reset_angle()
mb.reset_angle()
print("Motor A angle: {}".format(ma.angle()))
print("Motor B angle: {}".format(mb.angle()))
ma.run_target(80,1000,legoapi.Then.Brake)
mb.run_target(80,1500,legoapi.Then.Brake)
time.sleep(3)
print("Motor A angle: {}".format(ma.angle()))
print("Motor B angle: {}".format(mb.angle()))
print("8")
cs = legoapi.ColorSensor(legoapi.Input.Port1)
print(cs.ambient())
print("9")
ts = legoapi.TouchSensor(legoapi.Input.Port2)
print(ts.pressed())
# ...
The API is almost the same as the Pybricks API for EV3.
The follwing diffrences are here mentioned:
- Class EV3Brick is not implemented
- Motor constructor has only the port argument
- Motor.speed() is not implemented
- Motor.reset_angle(angle) takes no argument so its reset_angle()
- Motor.run_until_target(...) is not implemented
- Motor.dc(...) is not implemented
- Motor.track_target(...) is not implemented
- Motor.control is not implemented
- ColorSensor has only the ambient() function
- InfraredSensor is not implemented
- UltrasonicSensor.distance() has no optional argument silent
- UltrasonicSensor.presence() is not implemented
- GyroSensor.speed() is not implemented
- GyroSensor constructor has only the port argument