using different frequencies

Kris Cardoen · 2013-01-28 12:33

Hi,

Normally I use the following freq in my programs

> system.Clock(80_000_000) 'Setting the clock

Now, I have connected encoders that support up-to Frequency = up to 30khz

I'm having trouble using the encoders, I guess that 80kz is too fast...

But when I change my setting to system.Clock(25_000_000) for example my Parallax Serial Terminal Plus gives strange symbols.

Is it possible to have different fequencies for different cogs and if not how can I solve this problem?

 OBJ  Encoder : "Quadrature Encoder"
  pst     : "Parallax Serial Terminal Plus"
  pin     : "Input Output Pins"                'instance for using I/O pins
  time    : "Timing"                           'instance for timing
  system  : "Propeller Board of Education"     'instance for board of education    


VAR
  long Pos[3]                            'Create buffer for two encoders (plus room for delta position support of 1st encoder)
  long forwardCounts
  long backwardsCounts 
PUB Main
  system.Clock(30_000_000) 'Setting the clock                                  'Initialise clock  
  pst.Start(115_2000)  
  Encoder.Start(0, 1, 1, @Pos)           'Start continuous two-encoder reader (encoders connected to pins 8 - 11) 
  repeat
    pst.Str(String("pos 0 = "))
    pst.dec(Pos[0])
    pst.newline


    pst.Str(String("forwardCounts = "))   
    '<read Pos[0]
    ' or Pos[1] here>         'Read each encoder's absolute position
    forwardCounts := Encoder.ReadDelta(0)   'Read 1st encoder's delta position (value since last read)
    pst.Dec(forwardCounts)
    pst.newline
    time.Pause(2000)

any help would be much appriciated

jmg · 2013-01-28 13:28

Kris Cardoen wrote: »

Now, I have connected encoders that support up-to Frequency = up to 30khz

I'm having trouble using the encoders, I guess that 80kz is too fast...

This does not quite make sense. Where does ' that 80kz ' come from ?
What does 'trouble using' mean, exactly ?

Encoders are state/edge based, so will work from seconds-per-click, up to some HW/SW ceiling, and usually a library will say what it is tested to.
Some libraries will give error flags on illegal states, which can indicate over-run issues, and/or they may miss counts above a certain rate.

Kris Cardoen · 2013-01-28 13:59

I've got the system.Clock(80_000_000) from the examples http://learn.parallax.com
I'm quite new at this so please forgive my ignorance :-)

I was not able to read the signals from the encoders. Because it says max 30MZ max for the encoders I was wondering if
I had to modify my setting in the spin code to a lower value.

If I understand from your feedback this should not be a problem.
I guess I will have to look at the output signal of the encoders, maybe there is another reason for the problem.

Anyway thanks for helping to rule out this as a possible problem.

jmg · 2013-01-28 14:13

Kris Cardoen wrote: »

I was not able to read the signals from the encoders. Because it says max 30MZ max for the encoders

but above you said 30KHz ? - where exactly is 'it says' ?

Kris Cardoen wrote: »

If I understand from your feedback this should not be a problem.
I guess I will have to look at the output signal of the encoders, maybe there is another reason for the problem.

Can you control the speed of the encoders ?
Do they count Ok at low speeds ?
You need to report what does work, and what does not, and what test points you have tried.

NWCCTV · 2013-01-28 16:15

but above you said 30KHz ? - where exactly is 'it says' ?

I think he meant MHz.

kuroneko · 2013-01-28 17:27

Kris Cardoen wrote: »

But when I change my setting to system.Clock(25_000_000) for example my Parallax Serial Terminal Plus gives strange symbols.

This method only accepts 5M/10M/20M/40M/80M as valid clock frequencies (see method description). Anything out of range will result in 5M overall speed which is too slow for 115200 baud.

using different frequencies

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