Go Down

Topic: From linear to exponential PWM output (Read 19 times) previous topic - next topic


If i correct the X for i then after the switch point the line goes straigth roof high. See screenshot.

If you're trying to store a curve in the array, why don't you just calculate the values you want and put them in a static initialiser?

If you're trying to approximate the curve with three straight lines then I don't see the benefit of the lookup table - you might just as well do a range check, scale and offset. If execution time is critical then you could implement that logic during setup and cache the result, but I'd still calculate it doing three linear transforms rather than trying to write it as a single expression. But the circumstances where it's sensible to pre-calculate a linear transform are pretty unusual imo.
I only provide help via the forum - please do not contact me for private consultancy.



Do not fully understand what you mean with Offline calculation of the mapping.


This whole slotrace controller project is not standard so we try the things step by step.
Currently all controllers that have an exponential curve just run from the startspeed point to full speed.

For those just stepping in and try to help.
With the selectable XY switchpoint we try to be different and this has not been tried or tested before.
Now for this step in the project we like only to curve the last straight line by changing a curve value.
1 is a straight line and 3 a full curve.
We have to test if good slot race drivers can benefit from this last line to be linear or to be curved.
Also even if the lines are linear we not yet tested with drivers if this would be enough and the curving is not needed at all.
But I like to have it already and then test drive all possible options at one day to have comprehensive comparising with same drives and track conditions.

All settings to XY and curve value need to be changeable while the controller is plugged in and in use.

This is where the project currently stands and we are not ready yet.
I am eager to learn but my level of programming and mathematics in not at the same level you guys are. :-(

Your given options are acabadabra to me so I cant say if this or that would be better or give an other result that is desired.

Cheers, Paco

Never to old to learn and I learn every day



Can you chime in?.
SpeedfinaleValue never starts at speedstartValue when the lookuptable is used.
VB nicely shows the lookuptable is filled with correct values.
If startspeed is 100 and Y value is 175 as soon as the trigger leaves deadband zone it jumps to 183 instead of 101.
Looks like it does not use the first part of the line from startspeed to XY point.

Code: [Select]
void fillLookupTable()
  speedstartValueold = speedstartValue;
  switchpointXValueold = switchpointXValue;
  switchpointYValueold = switchpointYValue;


  switchpointXValue = constrain (switchpointXValue,deadbandXvalue, 255);
  switchpointYValue = constrain(switchpointYValue,speedstartValue, 255);
  for (int i=0; i<256; i++)
    if (i < deadbandXvalue)
      lookupTable[i] = 0;
    //++ knicked powerline at X and Y value ++ SETTING
    if (i < switchpointXValue)
    lookupTable[i] = map(i, 0, switchpointXValue, speedstartValue, switchpointYValue);
    lookupTable[i] = map(i, switchpointXValue, 255, switchpointYValue, 255 );       // this could get replaced by a curve after all is working

It looks as it does not use the
Code: [Select]
lookupTable[i] = map(i, 0, switchpointXValue, speedstartValue, switchpointYValue);

and always starts from the XY Value point set.


Never to old to learn and I learn every day


Can you post the output of the function?
What are the values used in the function??
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)


Rob the output of the function I read too into the VB application for displaying where the immidiate screen nicely show the lookuptable values to be correct and start at 104 and go upto 255.
See the screenshot.

Never to old to learn and I learn every day

Go Up