Servo - July 2008

website at www.servomagazine.com. Here’s the code that will put the menu up in a terminal emulator window:

void show_menu(void)
{

 cls();
 cls();
 printf(“%c[2;4H SERVO A3959 MOTOR CONTROL
MENU”,esc);
 printf(“%c[5;7H F - ROTATE CW”,esc);
 printf(“%c[6;7H R - ROTATE CCW”,esc);
 printf(“%c[7;7H S - STOP”,esc);

Entering an F, an R, or an S invokes the main routine code, which is looping continuously:

//*******************************************************
//* MAIN SERVICE LOOP
//*******************************************************
 show_menu();
 do{
 if(CharInQueue())
 {
 bytein = recvchar();
 switch(toupper(bytein))
 {
 case ‘F’:
 motion_HALT;
 mdelay1(100);
 motion_CW;
 break;
 case ‘R’:
 motion_HALT;
 mdelay1(100);
 motion_CCW;
 break;
 case ‘S’:
 motion_HALT;
 break;
 }

 }
}while(1);

The CharInQueue() function informs the main routine that a character is waiting in the EUSART’s external buffer. When a character arrives from the personal computer, we retrieve it from the external buffer and parse it. If the character is an F, we stop the BDPG-60-110-24V-3000-R326, wait for 100 ms and rotate the BDPG-60-110’s shaft in the clockwise direction. An incoming “R” stops the motor, waits for 100 ms, and forces the BDPG-60-110’s motor shaft to rotate in the counterclockwise direction. To stop the motor shaft, we simply drop the ENABLE line to a logical low. That’s all there is to it!

Spinning Out

My version of the A3959 motor controller is shown attached to its demonstration board in Photo 4. When you’re ready to put the A3959 to work in a real-world

PHOTO 4. You’ll want to build up an A3959 motor driver board without the socket if you plan to run a motor for an extended length of time. It is important to make sure that the A3959 heatsink tabs are soldered to the copper heatsink area.

SOURCES

Allegro MicroSystems — www.allegromicro.com A3959 A3959 Demonstration Board

Microchip — www.microchip.com PIC18F4620

HI-TECH Software — www.htsoft.com HI-TECH PICC- 18 C Compiler

Anaheim Automation — www.anaheimautomation.com BDPG-60-110-24V-3000-R326

motor driver application, be sure to solder the A3959 directly to the PCB. The A3959 tabs need to be soldered to a copper heatsink area provided on the PCB. Give the heatsink area as much of the PCB’s copper as you can.

The download package firmware was written using the HI-TECH PICC- 18 C compiler and contains lots of goodies you can use in other projects, such as timer manipulation routines, timer interrupt handlers, serial communication routines, and serial communications interrupt handlers. The A3959 is a really robust and easy to use part. I have no doubt you’ll have your aluminum human doing some heavy lifting in no time flat. See you next time! SV