Controlling *Servo Motor*s with an *RaspberryPi* + *Servo/PWM-Pi Hat!* using *MATLAB*

Hi, I have to control one or more Servo motors which are plugged in a Servo/PWM-Pi Hat which is plugged in a RaspBerryPi 3 on the other hand. VIA Matlab.

if true
  % >> rpi = raspi

rpi =

raspi with properties:

         DeviceAddress: 169.254.0.2                   
                  Port: 18732                         
             BoardName: Raspberry Pi 3 Model B        
         AvailableLEDs: {'led0'}                      
  AvailableDigitalPins: [4,5,6,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27]
  AvailableSPIChannels: {'CE0','CE1'}                 
     AvailableI2CBuses: {'i2c-1'}                     
      AvailableWebcams: {}                            
           I2CBusSpeed: 0                             

Supported peripherals

>> showPins(rpi) >> rpi.AvailableI2CBuses

ans =

cell

    'i2c-1'

>> rpi.I2CBusSpeed

ans =

     0

>> scanI2CBus(rpi,'i2c-1')

ans =

1×2 cell array

    '0x40'    '0x70'

>> i2csensor = i2cdev(rpi,'i2c-1','0x70')

i2csensor =

i2cdev with properties:

        Bus: 'i2c-1'
    Address: '0x70'

>> output1 = read(i2csensor,2)

output1 =

1×2 uint8 row vector

   17   17

>> output2 = readRegister(i2csensor,14)

output2 =

uint8

   0

>> i2csensor

%what do I type in here, to define the Servo motor which is connected to Pin 0 at the Servo/PWM Hat ?

>> s = servo(i2csensor,0) Undefined function 'servo' for input arguments of type 'raspi.internal.i2cdev'.

end

THANKS IN ADVANCE !!!!

[Kenan Wood]

Hi I had a bit of trouble with this too hope this helps.

With the data sheet for the PCA9685 https://www.nxp.com/docs/en/data-sheet/PCA9685.pdf and https://forums.adafruit.com/viewtopic.php?f=24&t=92012 is how I got mine to work.

   mypi = raspi;
   scanI2CBus(mypi,'i2c-1')
   i2cpwm = i2cdev(mypi,'i2c-1','0x40')

servoMin = 150;
servoMax = 600;

% Set all 4 PWM to 0
write(i2cpwm,[hex2dec('FA') hex2dec('0')])
write(i2cpwm,[hex2dec('FB') hex2dec('0')])

% To control all 16 servos in one write
% write(i2cpwm,[hex2dec('FC') hex2dec('0')])
% write(i2cpwm,[hex2dec('FD') hex2dec('0')])

while true
prompt = 'Set servo value between 0, 180 degrees (99 to exit): ';
degrees = input(prompt) 
    if degrees == 99
        return
    end
prompt = 'Select servo between 1, 16: ';
servoNum = input(prompt);

myServoWrite(degrees, servoMin, servoMax, i2cpwm, servoNum)
end

function myServoWrite(degrees, servoMin, servoMax, i2cpwm, servoNum)

offCount = floor(degrees/180 * (servoMax - servoMin) + servoMin)

write(i2cpwm,[(hex2dec('08') + 4*servoNum) bitand(offCount,hex2dec('FF'))]); % Low byte
write(i2cpwm,[(hex2dec('09') + 4*servoNum) bitshift(offCount,-8)]); % High byte 
end

[Tobias Schuster]

Hi Kenan, your script worked for me as well on Matlab R2021b and Raspberry Pi 4 B.

However, using the operating system of the file "mathworks_raspbian_R21.2.0.zip" coming from the MATLAB Support Package for Raspberry Pi Hardware, I'm not able to control the servos. I can execute the script without any error message, but nothing happens on the hardware.

So far, I managed to control a DC Motor (direction and speed) which is also connected to the same Raspberry Pi via a motor hat. By using built-in functions like "configurePin(rpi,Pin,'PWM')" or "writePWMDutyCycle(rpi,Pin,speed)" I can access the relevant GPIO Pins. Maybe there is a posibility to realise a servo motor control in a similar way.

The support package also provides the functions

s = servo(mypi, 12, 'MinPulseDuration', 1e-3, 'MaxPulseDuration', 2e-3);

and

writePosition(s, 90);

but I don't know how to acces the servo in this way. Maybe it is only possible if the servo is directly connected to the Raspberry Pi without the motor hat in between.

Thank you in advance!