Vincent Chan wrote:
>
> hi,
>         I just begin programming pic.  I have question about rc servo, motor a
nd
> sensor.  Do you know where can I find above items for cheap price?  Cost is
> my most important factor.
>         I am also wondering what kind of above items I should use.  I am just
> planning to build a little car that can detect object and avoid to collide
> with it and find a way around the object.  The main component of my car are
> just rc servo, motor, sensor, a regular(2"x6") breadboard(don't plan to do
> soldering my 16F84 for now)and chip;  so should not weight too much.
>         Also, I am wondering if I have to use seperate chips for each componen
t.
>         Do you know if there are any sample code and circuit for controller mo
tor,
> sensor and rc servo that I can read as reference?
>
> thanks. bye.

Vincent,
RC servos use a variable pulsewidth signal proportional to arm position
or speed.
U can use one PIC pin per servo for control ie
-> set up tmr0 for high frequency interupt.
-> use one counter per channel; decrement every interupt.
-> every interupt check counter for equal setpoint; if equal then turn
pulse on
-> every time a counter reaches zero turn pulse off.

-> you can use AN513 as a guide to analog to digital conversion off
digital pins, I have developed similiar code for this that goes even
further and uses macros.

for direct control of a DC motor I recomend the SGS Thomson L293D as a
quick and easy solution, two years ago I trained a PIC16C84 to
bidirectionally drive two geared motors using an X-Y joystick under I.R.
control with this setup. The L293D is power hungry even in low power
mode so helps to use a transistor/mosfet to it for a power down mode.

Be carefull driving mosfets in a bridge configuration, the internal
diodes can "cog" the motor and prevent proper PWM control with out
correct drive sequence, this takes 4 pins per bridge where as you can
get away with only 2 for a L293D bridge(2 per package).
regards,
Graham Daniel