Micro Serial Servo Controller

Support Servo controllers and servos
1

Hi,

I have one of your Micro Serial Servo Controllers but am having trouble
getting it to work.
I am using Pololu Mode with no jumper on the board.

When I power up the board the yellow LED comes on ok.
When I try to send data to the board, the red LED comes on and the green LED
flashes.
Even if I try to get the board to tell me the servo number settings.
This happens whatever baud rate I try and set.
e.g.

 // Open the serial port.
 g_hSerialPort = CreateFile (TEXT("COM1:"), // Pointer to the name of the 
port
       GENERIC_READ | GENERIC_WRITE, // Access (read/write) mode
       FILE_SHARE_READ | FILE_SHARE_WRITE,            // Share mode
       NULL,         // Pointer to the security attribute
       OPEN_EXISTING,// How to open the serial port
       0,            // Port attributes
       NULL);        // Handle to port with attribute to copy

 // If it fails to open the port, return FALSE.
 if ( g_hSerialPort == INVALID_HANDLE_VALUE ) {
  // Could not open the port.
  MessageBox (g_hWnd, TEXT("Unable to open the port"), TEXT("Error"), 
MB_OK);
  dwError = GetLastError ();
  return FALSE;
 }

 SerialPortDCB.DCBlength = sizeof (DCB);
 // Get the default port setting information.
 GetCommState (g_hSerialPort, &SerialPortDCB);

 SerialPortDCB.BaudRate = 9600;              // Current baud
 SerialPortDCB.fBinary = TRUE;               // Binary mode; no EOF check
 SerialPortDCB.fParity = FALSE;               // Enable parity checking.
 SerialPortDCB.fOutxCtsFlow = FALSE;         // No CTS output flow control
 SerialPortDCB.fOutxDsrFlow = FALSE;         // No DSR output flow control
 SerialPortDCB.fDtrControl = DTR_CONTROL_DISABLE ; // DTR flow control type
 SerialPortDCB.fDsrSensitivity = FALSE;      // DSR sensitivity
 SerialPortDCB.fTXContinueOnXoff = FALSE;     // XOFF continues Tx
 SerialPortDCB.fOutX = TRUE;                // No XON/XOFF out flow control
 SerialPortDCB.fInX = FALSE;                 // No XON/XOFF in flow control
 SerialPortDCB.fErrorChar = FALSE;           // Disable error replacement.
 SerialPortDCB.fNull = FALSE;                // Disable null stripping.
 SerialPortDCB.fRtsControl = RTS_CONTROL_DISABLE;          // RTS flow 
control
 SerialPortDCB.fAbortOnError = FALSE;        // Do not abort reads/writes on 
error.
 SerialPortDCB.ByteSize = 8;                 // Number of bits/bytes, 4-8
 SerialPortDCB.Parity = NOPARITY;            // 0-4=no,odd,even,mark,space
 SerialPortDCB.StopBits = ONESTOPBIT;        // 0,1,2 = 1, 1.5, 2


 // Configure the port according to the specifications of the DCB structure.
 if (!SetCommState (g_hSerialPort, &SerialPortDCB)) {
  // Could not create the read thread.
  MessageBox (g_hWnd, TEXT("Unable to configure the serial port"), 
TEXT("Error"), MB_OK);
  dwError = GetLastError ();
  return FALSE;
 }


 buff[0]=0x80;//start byte
 buff[1]=0x02;//device id
 buff[2]=16;//command number
 WriteFile(g_hSerialPort, &buff, 3, &len, 0);

Please advise what I am doing wrong.

Thanks
Simon

2

Your problem may be as simple as having your serial and ground communications lines swapped! I’m running a micro servo controller from a PC serial port, and that’s the LED pattern I see when I plug the connector in backwards. With a standard DB9 connector you want pin 5 to be ground, and pin 3 to go to the RS-232 serial input. The problem might be the same if you’re going through a logic-level converter to the TTL level inputs.

Your code looks fine to me, but if you’d like you can try this very simple one I made this morning for a co-worker to run a servo at our weekly meeting:
engin.umich.edu/~aborrell/prog/flipper.exe
It’s called flipper because the servo was actuating, well, a flipper on one of our robots. Anyway, it controls just one servo, and it will tell you all the key commands (and optional command-line arguments) when you run it the first time. If you’d prefer not to download and run a strange executable, here is the source code (in C for win32 console applications):

/*
Flipper Servo Demonstration Program
Adam Borrell
4/12/06
 */

#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <conio.h>

HANDLE openPort(int);
void put(int, int);
void move(int, int);
void servoOff();
HANDLE fd;

void main(int argc, char *parameters[])
{
	char input[32];
	int il=0,ol=0;
	int done=0;
	int min=2000, max=4000, step=50, neutral=3000, servoNumb=0;
	int ang;
    fd=openPort(CBR_19200);

	printf("Flipper Flipper\n\n");
	printf("Commmands:\n");
	printf("A - Increase servo position\n");
	printf("Z - Decrease servo position\n");
	printf("Q - Send servo to min\n");
	printf("W - Send servo to neutral\n");
	printf("E - Send servo to max\n");
	printf("Spacebar - Emergency Servo Stop (no effect on digital servos)\n");
	printf("Backspace - quit\n\n");
	
	if(argc==1){
		printf("Argument Format:\n");
		printf("Servo Neutral Position 500-5500 (Defualt 3000)\n");
		printf("Servo Min Position 500-5500 (Defualt 2000)\n");
		printf("Servo Max Position 500-5500 (Defualt 4000)\n");
		printf("Servo Step Size (Defualt 50)\n");
		printf("Servo Number (Default 0)\n\n");
	} else {
		if(argc>1){
			neutral=atoi(parameters[1]);
		}
		if(argc>2){
			min=atoi(parameters[2]);
		}
		if(argc>3){
			max=atoi(parameters[3]);
		}
		if(argc>4){
			step=atoi(parameters[4]);
		}
		if(argc>5){
			servoNumb=atoi(parameters[5]);
		}
	}

	ang=neutral;

	while (!done) {
		*input = getch();
		switch(*input){
			case 32:
				servoOff();
				printf("Emergency Servo Stop\n");
				break;
			case 8:
				done = 1;
				break;
			case'a':
				if(ang<=(max-step)) ang+=step;
				put(servoNumb,ang);
				break;
			case'z':
				if(ang>=(min+step)) ang-=step;
				put(servoNumb,ang);
				break;
			case'q':
				ang=min;
				put(servoNumb,ang);
				break;
			case'w':
				ang=neutral;
				put(servoNumb,ang);
				break;
			case'e':
				ang=max;
				put(servoNumb,ang);
				break;
			
			default:
				break;
		}
	}
	servoOff();
	printf("done!\n");
	return;
}

void put(int servo, int angle) {
	unsigned char buff[6];
	DWORD len;

	unsigned short int temp;
	unsigned char pos_hi,pos_low;
	
	temp=angle & 0x1f80;
	pos_hi=temp>>7;
	pos_low=angle & 0x7f;

	buff[0]=0x80;//start byte
	buff[1]=0x01;//device id
	buff[2]=0x04;//command number
	buff[3]=servo;//servo number
	buff[4]=pos_hi;//data1
	buff[5]=pos_low;//data2
	WriteFile(fd, &buff, 6, &len, 0);

	printf("%s%d\n", "Servo Position ", angle);

	return;
}

void servoOff() {
	unsigned char buff[6];
	DWORD len;
	int servo;

	buff[0]=0x80;//start byte
	buff[1]=0x01;//device id
	buff[2]=0x00;//command number
	buff[4]=0x0f;//data1
	for(servo=0;servo<8;servo++) {
    	buff[3]=servo;//servo number
    	WriteFile(fd, &buff, 5, &len, 0);
    	}    
	return;
}

HANDLE openPort (int baud) {
	HANDLE fd;
	COMMTIMEOUTS joy_timeouts = {0,0,0,0,0};
	DCB joy_dcb;
	fd=CreateFile("COM1", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, 0, 0);
	if(fd==INVALID_HANDLE_VALUE) {
		fprintf(stderr, "BOO: Could not open COM1 port!\n");
		return (HANDLE) -1;
	}
	if(!GetCommState(fd, &joy_dcb)){
		CloseHandle(fd);
		fprintf(stderr, "BOO: Could not read COM1 state!\n");
		return (HANDLE) -1;
	}
	joy_dcb.BaudRate=baud;
	joy_dcb.ByteSize=8;
	joy_dcb.fParity=0;
	joy_dcb.Parity=NOPARITY;
	joy_dcb.StopBits=ONESTOPBIT;
	if(!SetCommState(fd, &joy_dcb)){
		CloseHandle(fd);
		fprintf(stderr, "ERROR: Could not set COM1 State!\n");
		return (HANDLE) -1;
	}
	if(!SetCommTimeouts(fd, &joy_timeouts)){
		CloseHandle(fd);
		fprintf(stderr, "ERROR: Could not set COM1 Timeouts!/n");
		return (HANDLE) -1;
	}
	return fd;
}

Another potential problem is the one I had with my first Pololu micro servo controller…after I accidentally shorted power to the TTL input pin (puff of smoke, sad day). Servos connected to it still go to their neutral positions after I start sending commands of any sort, and sometimes it takes a few just flashing the green light, but sooner or later I get a different pattern of unhappy looking LED flashing.

Anyway, I hope some of this helps. Please post to let us all know how it works out!

3

Many thanks for the quick reply, and thanks for the code.

After laying awake last night I found the problem!

I was testing the controller with a serial cable with 2 wires jammed into the plug. It turns out that my serial cable is a NULL modem cable so pins 2 and 3 are crossed (Doh!)
As soon as I connected it to the right pin it worked fine!

Now all I have to do is modify the servos for linear motion!

Thanks again
Simon