Picbasic serial commands

I am interfacing with a PIC16F84 using the RS232 serial port. I am using Picbasic to compile the software for the microcontroller.

currently this is my MCU code -

Code:

---

  Include "modedefs.bas"  ' Include serial modes
si    var  PORTA.0
pos    var  byte
servo  var  byte
cont  var  byte
trisb = 0  'make all of port B outputs

start:
  serin si,N2400,servo,pos
for cont = 0 to 50
  pulsout  servo,pos
  pause    15
next      cont
  goto    start

---

It is to control an array of servo motors.

There is a problem with the code, in that when i send the servo and pos data to the chip, it pulses the servos 50 at the required rate. Then it stops and the servo can move out of place again.

Is there any way i can create a loop that checks for any data coming in. If not it pulses it again before looping back, if there is data, it collects it, changes the values of the variables accordingly, luses, and then loops.

Thanks

Harry

This really should be in the Other Basic forum, but ...

There are two ways of holding the servo in its current position:

1) If you're controlling the servo directly (not through a servo controller chip) - keep DC on the last pair of poles.

2) Using a selsyn (or other position sensor), ALWAYS turn the servo to the required position with a voltage proportional to the error. If it's in the right position the voltage will be 0. As soon as it moves it'll get a pulse driving it in the opposite direction. (You don't even need a servo with this method - any DC motor will give you an accuracy of around 14-16 bits. That's about 1 part in 10^12 - it should be accurate enough for any real-world use. This is the method used to drive the 5 axes of the Zeiss planetarium projector in the Hong Kong Space Museum.)

Quote:

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Originally Posted by Al42

This really should be in the Other Basic forum, but ...

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Agreed. :)

Moved

Is the drive tuned correctly?
When the drive is tuned to the motor you should have a stiff shaft (no comments from the peanut gallery please)
The motor should not drift unless the load is heavier than then the motor can stabilize. Sounds like you may have some slop.
How much is the motor moving out of place?