Edge finding improvements

A

AllyCat

Senior Member
Hi,

That's the second time the forum software has done that to me recently. Hopefully fixed now.

Cheers, Alan.
 
B

BESQUEUT

Senior Member
erco said:
edmunds: Sounds like you are making good progress. Getting back to that similar project in the Parallax forum, I'm attaching the BS2 code here, which could be tweaked to run in PICAXE BASIC. At a quick glance, I see that for speed, Phil only looked at the even # pixels.

Code: 
' =========================================================================
'
'   File...... tsl1401_follower.bs2
'   Purpose... Line follower program for the BOE-Bot, using the TSL1401-DB.'
'   Author.... Phil Pilgrim, Bueno systems, Inc.
'   E-mail....
'   Started... 18 August 2007
'   Updated... 28 November 2009
'
'   {$STAMP BS2}
'   {$PBASIC 2.5}
'
' =========================================================================


' -----[ Program Description ]---------------------------------------------

' This program uses the TSL1401-DB linescan imager daughterboard in
' conjunction with a BASIC Stamp 2 on a BOE-Bot to guide the BOE-Bot along
' dark line made with black tape on a light-colored floor.

' -----[ I/O Definitions ]-------------------------------------------------

ao       PIN 0            'TSL1401R's analog output (threhsolded by Stamp).
si       PIN 1            'TSL1401R's SI pin.
clk      PIN 2            'TSL1401R's CLK pin.
led      PIN 3            'LED strobe input.
servopal PIN 12           'ServoPAL control pin.

' -----[ Constants ]-------------------------------------------------------

DARK     CON 0            'Value assignd to "which" for dark pixels.
LIGHT    CON 1            'Value assigned to "which" for light pixels.

' -----[ Variables ]-------------------------------------------------------

pdata    VAR Word(8)      'Pixel data, as acquired LSB first from sensor.
pixels   VAR pdata.BIT0   '128-bit pixel array mapped onto pdata.
exp      VAR Word         'Exposure (integration) time in 2uSec units.
avg      VAR Word         'avg for averaging.
i        VAR Byte         'General-purpose index.
cnt      VAR Byte         'Result of pixel-count routine.

' -----[ Program Code ]----------------------------------------------------

which    CON DARK                      'Set for dark line on light floor.
                                       'Change to LIGHT, otherwise.
line     CON 22 >> 1                   'Line width for 1/2-inch tape.
                                       'Adjust proportionally for other sizes.

INPUT servopal                         'Wait for ServoPAL to power up.
DO: LOOP UNTIL servopal
LOW servopal                           'Reset the ServoPAL.
PAUSE 100
HIGH servopal

exp = 15                               'Set initial exposure (strobe) time.

DO                                     'Begin the scan-and-process loop.
  GOSUB GetPix                         'Obtain a pixel scan.
  GOSUB AvgPix                         'Find the dark pixel count and
                                       'average position.
  DEBUG HOME, DEC avg, " ", DEC cnt, CLREOL 'For testing...
  IF (cnt < line - 2) THEN             'If count is too low,
    exp = exp - 1 + (which << 1)       'Adjust exposure according to line color.
  ELSEIF (cnt > line + 2) THEN         'If too high,
    exp = exp + 1 - (which << 1)       '  adjust the other way.
  ENDIF
  exp = exp MIN 1 MAX 20               'Make sure exposure time is reasonable.
  IF (cnt >= line >> 1 AND cnt <= line << 1) THEN 'If count isn't WAY off, use position.
    IF (avg <= 64) THEN                'If line is to the left,
      PULSOUT servopal, 718            '  steer left proportional to the error.
      PULSOUT servopal, 750 + (avg >> 1)
    ELSE                               'Else, if line is to the right,
      PULSOUT servopal, 750 - (127 - avg >> 1) '  steer right proportional to the error.
      PULSOUT servopal, 782
    ENDIF
  ELSE                                 'If pixel count is WAY off,
    PULSOUT servopal, 2000             '  just stop until we get the
    PULSOUT servopal, 2000             '  exposure time right.
  ENDIF
LOOP

' -----[ Subroutines ]-----------------------------------------------------

' -----[ GetPix ]----------------------------------------------------------

' Acquire 128 thresholded pixels from sensor chip.
' exp is the exposure time in microseconds.

GetPix:

  SHIFTOUT si, clk, 0, [1\1]           'Clock out the SI pulse.
  PWM clk, 128, 1                      'Rapidly send 150 or so CLKs.
  PWM led, 1, exp                      'PWM LED low for exposure time.
  SHIFTOUT si, clk, 0, [1\1]           'Clock out another SI pulse.
                                       'Read 8 words (128 bits) of data.
  SHIFTIN ao, clk, LSBPRE, [pdata(0)\16, pdata(1)\16, pdata(2)\16, pdata(3)\16]
  SHIFTIN ao, clk, LSBPRE, [pdata(4)\16, pdata(5)\16, pdata(6)\16, pdata(7)\16]
  RETURN

' -----[AvgPix]------------------------------------------------------------

' Find average location of pixels of the type indicated by which (0 = dark;
' 1 = light). For the sake of speed, consider only the even pixels. The
' position will still cover the full range, but the count will be half of
' what it would be if if every pixel were considered.

AvgPix:

  cnt = 0
  avg = 0
  FOR i = 0 TO 127 STEP 2
    IF (pixels(i) = which) THEN
      avg = avg + i
      cnt = cnt + 1
    ENDIF
  NEXT
  IF (cnt) THEN avg = avg / cnt
  RETURN
Click to expand...
Averaging black pixels is the best algorithm to find center of line.
I just explain that in the other thread Signed-numbers-in-a-PID-statement
But this has nothing to do in an "edge finding" thread as it does not rely on finding edges...
 
S

stan74

Senior Member
"Certainly far larger than would have gone through my letterbox (that's a 15 cm ruler)"
Alan,I had to send a package back and the post office have a "standard letter box" they see if it will go through but it's smaller than my letter box which is in a upvc front door. It' a con.
I am thinking of a line follower section in the robot parts of the forum and stick my 1st effort in there and other interesting stuff like this in there under a different heading. Any thoughts about some organisation of threads that so easily go off topic :) ?
 
Buzby

Buzby

Senior Member
That TSL 1401 chip is obsolete, as is the TSL 214 which I've had in my bits box for 20 years, literally !.

Dusted it off, plugged into bread board, added some code, and it works !.

TSL214_on_breadboard2.png

Now what do I do with it ?
 
B

BESQUEUT

Senior Member
Buzby said:
That TSL 1401 chip is obsolete, as is the TSL 214 which I've had in my bits box for 20 years, literally !.

Dusted it off, plugged into bread board, added some code, and it works !.

View attachment 20751

Now what do I do with it ?
Click to expand...
Maybe you can draw a line on a white paper and show it to your TSL.
So you can add to your code a sertxd to show how far from center you are and/or what is the current steering command.
 
E

edmunds

Senior Member
Buzby said:
That TSL 1401 chip is obsolete, as is the TSL 214 which I've had in my bits box for 20 years, literally !.
Click to expand...
TSL 1401 CL is not really obsolete, I'm sure you can get some if you really try. Even with the big lens on, like in the parallax/basic stamp design. But it is not recommended for new designs. However, TSL 1401 CCS, which is what I'm using is new and in full production and one of the few linear photo diode arrays out there with 'hold' function and reasonable number of pixels (<256).

Buzby said:
Now what do I do with it ?
Click to expand...
Build a line-follower! Seems several people have got the bug already :). Your 64 pixels are a tad easier to deal with than 128 I have.


Cheers,

Edmunds
 
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