==== Pan-Tilt unit Megarobot ==== Pan-Tilt Unit consits of two drives AI-701 manufactured by Megarobotics. Drive AI-701 form a servo which is controlled by commands via RS-232 interface. The servo directly interprets commands. There is no intermediary control unit between the PC and the drive. There are two drives always connected to the one computer via RS-232 bus. Recipient of the control command is determined by the identification number (ID). The azimuth drive (horizontal) has ID == 0, and the drive for the elevation (vertical) has ID == 1. ** Do not change the ID ** -- you can easily cause malfunction of the device. For the same reasons, it is also prohibited to change the speed of the serial communication interface (baud rate). * Manufacturer ([[http://www.megarobot.net/|MEGAROBOT.NET]]) provides also manual {{:help:common:aimotor701_manual_megarobot.pdf|AI-701}}. * For simple testing, one can use the "AI MOTOR - Tool v1.26", which is already installed in the workplace. * We encourage the student to read a short description of the "{{:help:common:zaciname_s_aimotorem.pdf|Zacínáme s AI-MOTORem}}", provided by ([[http://www.megarobot.net/|MEGAROBOT.NET]]), where the first step of working with the drive in that program are described. ==== How to control the PT unit ==== Pan-Tilt unit can be controlled in MATLAB using [[http://www.mathworks.com/help/matlab/matlab_external/getting-started-with-serial-i-o.html|Serial Port I/O]]. - Pan-Tilt is initialized by the following sequence of commands

ser = serial('COM1');
set(ser,'BaudRate',57600);
fopen(ser);

- You can control the PT unit by writing corresponding control bytes (see {{:help:common:aimotor701_manual_megarobot.pdf|manuál}}) to the file ''ser'' using command ''fwrite''. - To simplify the PT control the following function is provided:ptmove(ser, pan_pos, tilt_pos); where ''pan_pos'' corresponds to the absolute rotation angle around vertical axis, ''tilt_pos'' corresponds to the absolute rotation angle around horizontal axis. Range of values for ''pan_pos'' and ''tilt_pos'' is from 0 to 254. It covers approximately 80 degrees in a given direction. To set the unit into the initial position (i.e. the position, where camera optical axis is perpendicular to the LCD screen) use the following values ''pan_pos==127'', ''tilt_pos==127''.

function ptmove(ser, pan_pos, tilt_pos, speed)
    if nargin<4
        speed = 3;
    end

    sermove(ser, speed, 0, pan_pos);
    sermove(ser, speed, 1, tilt_pos);
end

function sermove(ser, speed, pantilt, pos)
    b1 = uint8(hex2dec('ff'));
    b2 = uint8(bitshift(uint8(speed), 5) + uint8(pantilt));
    b3 = min(max(uint8(pos), uint8(0)), uint8(254));
    b4 = uint8(bitand(bitxor(b2, b3), uint8(hex2dec('7f'))));
    fwrite(ser, [b1 b2 b3 b4]);
end

- In the end, the communication is closed as follows:

fclose(ser);
delete(ser);