School Project - suggestions welcomed

g3cwi · 2012-02-21 12:53

Some lads at school have made a game with a racing car. Basically it consists of a rotating arm with a magnet on each end. This rotates below an acrylic racetrack. A small car is carried round by the magnet. The idea is to see how fast you can do 10 laps. If you go too fast the car flies off. I said that i would make a timing system for this using a Propellor Platform USB and the UI module. Jonny Mac's timer and LCD driver looked useful so I kludged together the following code:

obj

  ui : "jm_lcd_ui"

  Timer :"jm_etimer"



var

   Long mytimer[5] 
 
pub main | b


  ui.init         ' initialize LCD UI 
  Timer.init(16)  ' initialise timer
                        
  ui.cls          'A few graphics to start                                         
  ui.scrollstr(1, 1, 8, 250, @Congleton)                     
  ui.scrollstr(1, 2, 8, 250, @High)
                              
  Waitcnt(clkfreq + cnt)
  
  ui.cls 'display starting instructions
  ui.moveto(1, 1)
  ui.str(string("   Press"))
  ui.Moveto(1,2)
  ui.str(string("  Button"))                                                       
  
  
  repeat
    b := ui.getbtns      ' check buttons
                                                 

    ui.moveto(1, 1)                                          
    if (b & ui#BTN_ESC)
      ui.cls 'countdown from button press to race start
      ui.str(string("3"))
      
      Waitcnt(clkfreq + cnt)
      
      ui.cls
      ui.str(string("2"))
      
      Waitcnt(clkfreq + cnt)
      
      ui.cls
      ui.str(string("1"))
      
      Waitcnt(clkfreq + cnt)
      
      ui.cls 'the race starts
      ui.str(string("GO!"))
      Timer.Clear 'timer set to zero
      Waitcnt(clkfreq + cnt)

      

        Repeat 'this displays the time while the race is going
               'need some way to count 20 reedswitch closures
               'from race track and use that to halt timing
          ui.cls
          ui.moveto(1, 1)
          Timer.read(@mytimer)
          ui.dec(mytimer[1])
          ui.moveto (5,1)
          ui.str(string("Secs"))
          
          ui.moveto(1, 2)
          Timer.read(@mytimer)
          ui.dec(mytimer[0])
          ui.moveto (5,2)
          ui.str(string("ms"))
       
          Waitcnt(clkfreq/4 + cnt) 'update display every 250ms
           
      Timer.Hold 'race end detected somehow!
      
      ui.cls 'display the final time
      ui.moveto(1, 1)
      Timer.read(@mytimer)
      ui.dec(mytimer[1])
      ui.moveto (5,1)
      ui.str(string("Secs"))  'this does not work for some reason
          
      ui.moveto(1, 2)
      Timer.read(@mytimer)
      ui.dec(mytimer[0])
      ui.moveto (5,2)
      ui.str(string("ms"))     
      
    else
      ui.str(string("   ")) 'do I need this?

    

    waitcnt(clkfreq / 25 + cnt) 


dat

Congleton      Byte   "        Conglton", 0
High           Byte   "        High", 0

This only sort of works. The race will be monitor with a reed switch. 20 closures will equate to 10 laps at which point the timer must stop. Should I use a separate cog to count the pulses (and if so, how?) or should I do the detection in the main loop. If I use a separate cog, how do I use it to signal to the main object that the race has ended?

All ideas welcome.

Cheers

Richard N

Oldbitcollector (Jeff) · 2012-02-21 13:35

@Richard,

Yes you could create a separate cog for this and check it on each pass of your repeat loop..

Might be even easier to create a "lapcount" variable and do a lapcount++ at each pass of your repeat loop, then an IF statement to see if lapcount > 20, meaning end of race.

OBC

JonnyMac · 2012-02-21 14:00

If the pulses are clean then you could use a counter in EDGE DETECT mode to count them independent of the rest of your code.

groggory · 2012-02-21 14:06

JonnyMac wrote: »

If the pulses are clean then you could use a counter in EDGE DETECT mode to count them independent of the rest of your code.

Or if they're not clean you can clean them up with a little circuitry similar to a button debounce circuit.

JonnyMac · 2012-02-21 14:15

Or if they're not clean you can clean them up with a little circuitry similar to a button debounce circuit.

A 555 in single-shot mode is easy to implement. Or, one could write a debouncing cog to clean-up input pulses and count them.

groggory · 2012-02-21 14:45

JonnyMac wrote: »

debouncing cog to clean-up input pulses and count them.

I like this solution. It means no extra circuitry for the op.

jmg · 2012-02-21 16:04

Or, if you want to avoid adding delays to your sensor, you can use either of
a) SPDT reeds wired to a CMOS or PinKeeper input, has no bounce effect as the contacts either connect to Vcc or GND - any open time, holds the previous state.

b) Use 2 SPNO reeds, spaced so they cannot both be on, one to Vcc, one to GND, operates as in a).

in both cases the leading edge will be the precise contact closure

School Project - suggestions welcomed

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