Help with pwm and servos.

Angel

Would someone help me, I can't get to work the SX for controlling a hobby servo , I tried the PWM command, but its giving me some error that says "byte parameter expected"

what I wrote., well actually I used the template that comes in the help.

**********
'

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' Device Settings
'

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DEVICE········· SX28, OSC4MHZ, TURBO, STACKX, OPTIONX
FREQ··········· 4_000_000
'

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' IO Pins
'

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Sio············ VAR···· Ra.0··················· ' 1 IO pin
'

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· INTERRUPT
'

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ISR_Start:
· ' ISR code here
ISR_Exit:
· RETURNINT ' {cycles}································
' =========================================================================
· PROGRAM Start
' =========================================================================
Pgm_ID:
· DATA· "SX/B Template", 0
'

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' Program Code
'

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Start:
· ' initialization code here

Main:
· ' main code here
pwm RA.0, .0015, 8· 'What I expect here is that on port RA.0 i will get a PWM signal with .0015 seconds of duty cycle and for 8 seconds of duration.

· GOTO Main

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the idea·of the·project·is to control a robot and to vary the times on each servo to make it move while the other servos stay in the same position..., I know I am far from that, but, well I gotta make 1 servo move first lol..

thanks.

Jon Williams

PWM is not for motor control; it is used for charging an RC network to create an analog ouput (which should be buffered). For servo control you need to use PULSOUT or, when you get more advanced, use an interrupt-driven routine that can update your servos in the "background."

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Jon Williams
Applications Engineer, Parallax

Angel

I had the feeling something was wrong, but aren't the signals that control servos similar to pwm? maybe not.. well thanks , I will check that pulseout command, thanks

Mike Cook

Angel,

Here's a little SX/B program that operates a servo. This was just for testing the movement for various positions, should be commented enough to determine it's operation.

Mike

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Post Edited (Mike Cook) : 3/2/2006 11:38:17 PM GMT

Jon Williams

PULSOUT is used to send the pulse, and you'll need to do it every 20 milliseconds or so (unless you're using a digital servo).· If you want to do it in the background, you'll need an ISR -- which is possible in SX/B as you can see from the attached demo.

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Jon Williams
Applications Engineer, Parallax

Angel

Thanks Mike Cook and Jon Williams , I will check the files