Giving out pulses using propeller chip

Comments

• JonnyMac Posts: 9,550

  2010-08-04 20:02 edited 2010-08-04 20:02

  I wrote the attached program a couple months ago. It actually launches another Spin cog that serves as an 8-channel servo driver. As the whole thing is coded in Spin you might find it helpful.
  
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  Jon McPhalen
  Hollywood, CA
  
  Post Edited (JonnyMac) : 8/4/2010 8:14:29 PM GMT

  spin

  spin

  jm_servo8_ez.spin

  5K

  jm_servo8_ez.spin 4.8K
• Javalin Posts: 892

  2010-08-04 20:04 edited 2010-08-04 20:04

  have you looked at the servo objects in the OBEX? http://obex.parallax.com
  
  It does look like your code is wrong.· Maybe :
  

  us := clkfreq / 1_000_000   ' micro-seconds
  ms := clkfreq / 1_000       ' milliseconds
   
  twenty_ms := ms * 20        ' so we don't have to count each time
  one_pt_five_ms := us * 1500
   
  repeat
      outa[noparse][[/noparse]Led] := 1
      waitcnt(one_pt_five_ms + cnt)
      outa[noparse][[/noparse]Led] := 0
      waitcnt(twenty_ms + cnt)
  

  
  Might be a simple way to do it.· Note the indentation!
  
  edit - or this is a better way, as it provides a syncronised 1.5ms pulse - i.e. it begins every 20ms, rather than every 21.5ms as in previous loop.· (look at page 220 in the propeller manual)
  
  

  VAR
      long    syncDelay
      long    ms, us
   
  PUB Start
   
      us := clkfreq / 1_000_000     ' micro-seconds
      ms := clkfreq / 1_000         ' milliseconds
   
      twenty_ms := ms * 20          ' so we don't have to count each time
      one_pt_five_ms := us * 1500   '
   
      dira[noparse][[/noparse]Led]~~                   ' set to output
      syncDelay := cnt              ' setup syncronised delays
   
      repeat
          outa[noparse][[/noparse]Led] := 1
          waitcnt(one_pt_five_ms + cnt)     ' wait for 1.5ms
          outa[noparse][[/noparse]Led] := 0
          waitcnt(syncDelay += twenty_ms)   ' wait for the remainer of the 20ms
  
  

  
  
  James
  
  Post Edited (Javalin) : 8/4/2010 8:25:03 PM GMT
• prabhat Posts: 4

  2010-08-04 20:34 edited 2010-08-04 20:34

  I tried both the codes.. But surprisingly the same thing keeps happening. its driving me nuts because I am sure the mistake is something very fundamental. My servo would also wind up at one extreme and in fact pushing to go past it.
• Javalin Posts: 892

  2010-08-04 20:39 edited 2010-08-04 20:39

  what crystal and hardware board are you using?
  
  james
• prabhat Posts: 4

  2010-08-04 20:42 edited 2010-08-04 20:42

  I am using the prop stick usb platform. It has a 5 Mhz built in crystal
• W9GFO Posts: 4,010

  2010-08-05 01:30 edited 2010-08-05 01:30

  Are you sure that you have the servo hooked up correctly?
  
  waitcnt((clkfreq/1_000_000) * 1500 + cnt) is easier to understand (in my opinion) and will work at any _clkmode or _xinfreq without modification.
  
  Rich H
  
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  The Simple Servo Tester, a kit from Gadget Gangster.
• Javalin Posts: 892

  2010-08-05 08:09 edited 2010-08-05 08:09

  >waitcnt((clkfreq/1_000_000) * 1500 + cnt)
  but requires the delay to be calculated each and every time you run the line.
  >will work at any _clkmode or _xinfreq without modification.
  so will mine.
  
  I'll run up the code on my dev board tonight & put the o'scope to work on it.
  
  Cheers,
  
  James
• Javalin Posts: 892

  2010-08-05 17:23 edited 2010-08-05 17:23

  Code from the second example posted works fine - full code·as run on my·prop-demo-board·is:

  CON
      _clkmode                = xtal1 + pll16x
      _xinfreq                = 5_000_000
      LED                     = 5
  VAR
      long    syncDelay
      long    ms, us
      long    twenty_ms, one_pt_five_ms
   
  PUB Start
   
      us := clkfreq / 1_000_000     ' micro-seconds (so we don't calc each time)
      ms := clkfreq / 1_000         ' milliseconds
   
      twenty_ms := ms * 20          ' so we don't have to calculate each time
      one_pt_five_ms := us * 1500   '
   
      dira[noparse][[/noparse]Led]~~                   ' set to output
      syncDelay := cnt              ' setup syncronised delays
   
      repeat
          outa[noparse][[/noparse]Led] := 1
          waitcnt(one_pt_five_ms + cnt)     ' wait for 1.5ms
          outa[noparse][[/noparse]Led] := 0
          waitcnt(syncDelay += twenty_ms)   ' wait for the remainer of the 20ms
  

  
  Attachments to this post show the 1.5ms pulse (1ms per division) and the 20ms gap between the pulses (5ms per div).
  
  Cheers,
  
  James

  

  

  1_5_ms_pulse.jpg

  800 x 600 - 86K

  

  

  20ms_gap.jpg

  800 x 600 - 86K

  1_5_ms_pulse.jpg 86.1K

  20ms_gap.jpg 85.6K