Hello All,
I am newbie trying to learn some basic microcontroller programming. I am trying to control a servo (Tower PRO SG-50) using MSSC in Mini SSCII mode. Both MSSC and Baby-O are powered by a voltage regulator connected to a wall-wart. Here’s the code running on my Baby-O (I am using AVRLib for serial IO):
#include <avr/io.h> // include I/O definitions (port names, pin names, etc)
#include <avr/interrupt.h> // include interrupt support
#include "global.h" // include our global settings
#include "timer.h"
#include "buffer.h"
#include "uart.h"
#define START_POS 20
#define END_POS 200
void MoveServo(u08 Pos)
{
uartSendByte(0xFF);
uartSendByte(0x08);
uartSendByte(Pos);
}
int main(void)
{
uartInit();
uartSetBaudRate(9600);
u08 Pos = START_POS;
double Ctr;
while(1)
{
MoveServo(Pos);
Pos += 10;
if ( Pos > END_POS )
{
Pos = START_POS;
}
Ctr = 20000.0;
while(Ctr-- > 0.0);
}
}Running this code causes the servo to move to some random location and then it does not move any further. I was expecting the servo to move from one end to another in small steps. The green LED blinks on the controller as expected. A video showing the outcome can be found at http://www.youtube.com/watch?v=6mabttoQRqE
To debug, I connected the RX/TX from Baby-O to Pololu USB AVR Programmer in USB-Serial adapter mode (in addition to the signal pin on MSSC) and was able to verify that the commands sent to the MSSC matched the documentation (255 - 8 - Pos - where Pos value changed from START_POS to END_POS). This confirms that the Baby-O is indeed sending the correct data to the MSSC.
Also, I wrote a small C# program to control the MSSC from Windows. This program was able to control the MSSC and the same servo worked fine. Here’s the windows code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.IO.Ports;
namespace TestServoControllerCommands
{
class Program
{
private static SerialPort _com4 = new SerialPort("COM4", 9600, Parity.None, 8, StopBits.One);
private static int _ServoNumber = 0;
static void Main(string[] args)
{
_com4.DataReceived += new SerialDataReceivedEventHandler(_com4_DataReceived);
Console.WriteLine("Hit ENTER to open the serial port on COM4");
string cmd = Console.ReadLine();
_com4.Open();
if (cmd.ToLower().CompareTo("control") == 0)
{
ControlServo();
}
else
{
}
Console.ReadLine();
Console.WriteLine("Closing COM4 serial port");
_com4.DiscardInBuffer();
_com4.DiscardOutBuffer();
_com4.Close();
}
private static void ControlServo()
{
string pos = Console.ReadLine();
int nPos = 0;
while (pos.ToLower().CompareTo("end") != 0)
{
if (Int32.TryParse(pos, out nPos))
{
if (nPos >= 0 && nPos < 255)
{
MoveServo(nPos);
}
}
pos = Console.ReadLine();
}
}
private static void MoveServo(int nPos)
{
byte[] data = new byte[] { 0xFF, 0x08, Convert.ToByte(nPos) };
_com4.Write(data, 0, 3);
}
static void _com4_DataReceived(object sender, SerialDataReceivedEventArgs e)
{
while (_com4.IsOpen && (_com4.BytesToRead > 0))
{
Console.WriteLine(_com4.ReadByte());
}
}
}
}The C# program confirmed that the MSSC and the servo are functional. The video showing this can be found at http://www.youtube.com/watch?v=lk0UTldk9Oc
At this point I have run out of ideas to debug the problem further. Any help would be appreciated…
Thanks
-VK