HEDS5540 optical encoder

[louislouis]

Thank You Richard for helping me. That's great, now the "core" of my distance meter works perfectly. Yes, the max. distance what I can measure is near six and a half meter which is enough for me. If I want to measure more than 6,5m simply zeroed the reading and start count from that point. Now I must implement negative reading when I go to opposite direction from zero the reading must be from -1..... to -655,3.
Your explanation helping me a lot, once again Thank You.

[louislouis]

I finally assembled my distance meter based on rotary optical encoder and precision wheel. But still I have problem with math and precision.
For example, wheel circumference is 157mm, and when I take a 30 revs the result must be 4710mm, but the MCU calculates only 4708,1mm which is 1,9mm difference. Is there a way to improve the precision?
I use Richard's math:
157/1440 = .109 mm per encoder tick
.109 * 256 * 10 = 279
distance * 10 = (counts * 279)/256

counter = enc_counter */ 279 
lcdout  Dec counter/10 ,".", dec counter//10     ; display counter value on LCD

The precision 0,1mm is enough for me, the max. measurable distance want be 6000mm. I try some change, if I improve the precision to 0.01mm then the max. measurable distance shortened to 600mm and this not enough.

[richard]

you could look at nbit math or use a pic18 and long vars

you can glean a bit more precision breaking the calc up a bit

where 43200 counts would give 4709.2

 
frac = enc_counter.lowbyte * 1090         
posn1  = div32 100          ;mm*100          ;mv 2790
posn2 = (enc_counter.highbyte&15) * 2791  ; mm*100   mv 41865
frac = (enc_counter.highbyte>>4) * 44657
posn3 =  div32 100                       ;mm     mv6698

posn3=  posn3 + (posn1+posn2)/100       ;mm
frac=   ((posn1+posn2)//100 +5)/10        ;round it up
serout2 PORTa.0,84, [13,10,#enc_counter,9,dec posn3,".",#frac       ]

[louislouis]

Hello Richard, thank you again for help. Your code works and take a little improvement. I make some changes, first got a smaller precision wheel dia. 25mm (circ. 78,53975mm) and divide the encoder reading /2. Now the encoder reading is only 720 per one rev.
The code is as follows:

Main_Loop:
enc_counter = enc_counter /2
if Flag = 1 then 
frac = enc_counter.lowbyte * 1090         
posn1  = div32 100          ;mm*100          
posn2 = (enc_counter.highbyte&15) * 2794  ; mm*100   
frac = (enc_counter.highbyte>>4) * 44680
posn3 =  div32 100                       ;mm     
posn3=  posn3 + (posn1+posn2)/100       ;mm
frac=   ((posn1+posn2)//100 +10)/10        ;round it up
 
Lcdout $fe, 1
lcdout  "Dist: ",dec posn3,".",#frac
Flag = 0
endif 
goto Main_Loop

Now I can measure up to 7100mm, but still more or less precise.
Next step will be order one of the PIC18x mcu and try long variables.
Here are suitable to use the same encoder reading code (written in ASM) and simple change the word var to long var?
I think its not that easy. When I have the 18x PIC I think, I will need more help with this project. Thanks.

[richard]

frac= ((posn1+posn2)//100 +10)/10 ;round it up

is incorrect , it will round the number up always

frac= ((posn1+posn2)//100 +5)/10 ;round it up

is the way to round the number up if the last digit is 5 or more

[richard]

using n-bit math

result

ready v3
turns 23 f 489
33609 3664.3145
turns 23 f 486
33606 3663.9875
turns 23 f 484
33604 3663.7694

 Include "N-Bit_MATH.pbp" 
 
enc_new VAR BYTE   bank0
enc_old VAR BYTE   bank0
enc_counter VAR WORD   bank0
Flag var BYTE        bank0
tmp         var  byte[4]
res         var  byte[4]
tmp1        var  byte[4]
posn        var WORD
turns       var word
frac        var WORD
 
 
 
; Set variable value @ startup
Flag = 1                   ;preset a value    for testing
enc_new = 0
enc_old= 0
enc_counter = 33609      ;preset a value    for testing

 
Main_Loop:     
if Flag = 1 then
turns=  enc_counter /1440
frac=   enc_counter //1440
serout2 PORTa.0,84, [13,10,"turns ",#turns,9,"f ",#frac ] 
if frac then
@  MOVE?CP 157000, _tmp  
@  MOVE?WP _frac, _tmp1  
@  MATH_MUL  _tmp1, _tmp, _res 
@  MOVE?CP 1440000, _tmp
@  MATH_DIV  _res, _tmp, _tmp1
@  MOVE?PW _tmp1, _posn
@  MOVE?CP 144, _tmp
@  MATH_DIV  REG_Z, _tmp, _tmp1
@  MOVE?PW _tmp1, _frac
endif
posn=posn+turns*157
serout2 PORTa.0,84, [13,10,#enc_counter,9,dec4 posn,".",dec4 frac       ] 
 
 
 
Flag = 0
endif
goto Main_Loop
end

[louislouis]

I try to compile your code. I downloaded the N-Bit_MATH.pbp include, but the compiler stops with this error message:
"Bad data type"

If I try to compile only the N-Bit_MATH.pbp (only for test) and its do not compile. Stops on first line:
REG_X VAR BYTE[PRECISION] BANK0 SYSTEM
with the same error message MCU is the same 16F628A, For test I try also 16F688 with the same result. Something I'am doing wrong, I think.