Sin

[AndyP]

Does anyone have any example code or have a good explanation of how to use the SIN operator? In the manual it says that SIN starts with a value in binary radians as opposed to normal degrees. I have done a few debug tests and have got quite weird results.

e.g
SIN 0 =0
SIN 255=65533
SIN 127=3

It says that the output is from -127 to 127 in two's compliment. Does that mean that -127 would be represented as 65408?

Regards,

Andy Peaple

[FinchPJ]

I realise the question was asked several years ago - I came across it on a search - the problem with SIN() and COS() in PICBASIC is that they return a twos complement number. Also they deal with "binary radians" (not the same as trig radians) where 0 is 0 degrees/radians and 255 is 360 degrees or 2PI radians.
Here is my solution to displaying a barchart of the sine wave function 128+sin(i)
(using http://www.picbasic.co.uk/forum/showthread.php?t=2359 to display):

Value var word 'must use word variable for BARGRAPH
twoC var byte 'must use byte variable
include "LCDbar_INC.bas"
'BARgraph Value, Row, Col, Width, Range, Style

'........... I use in a loop and increment i etc............

twoC = sin(i)
if (twoc & %10000000)=0 then PosS 'else negative 2's complement
' value = 127-((twoc ^ %11111111) +1) 'restore negative value
value = 126 - (twoc ^ %11111111) 'I wanted a 128 offset
goto ShowS
PosS: value = 128 + twoc
ShowS:
@ BARgraph _Value, 1, 0, 16, 256, lines

'............ Fiddle/pause and go round the loop..........

Peter Finch

[dragons_fire]

here is a link to a website i found a while ago, that helps with a lot of the math. the site was written for a basic stamp, but it all works out the same.

http://www.emesystems.com/BS2math3.htm#arcCos

and here has a bunch of other math functions for the stamp along with explaining some of the other functions that can be done with it..

http://www.emesystems.com/BS2index.htm

[BrianT]

Hello,
The code below was used in an incubator. The user could set the mean temperature and the range. The day was divided into 96 fifteen minute segments and at 6 AM and 6 PM the temperature was set to the user commanded mean temperature. the "range" is a sinusoidal function that adds or subtracts from the mean. For example a mean of 24 with a range of 10 would cause the incubator to be at 24 degrees at 6 AM and 6 PM. At noon the temperature would be 24 + 10 = 34 and at midnight the temperature would be 24 - 10 = 14 Celsius.


CalculateSetPoint:
read 0, meantemp
read 1, range
' SetPoint = 10* (meantemp + range * sine (timeslot * 255/96)) with allowances
' for the sign and integer truncation plus an 18 hour time shift.

w = (255 * timeslot/96) ' 0 to 255 in 2.667 chunks
b = sin w ' 0 to 127 in 2's complement
if b.7 = 1 then negative
positive:
x = 10*meantemp + (20*b*range/255)
goto timeslotdone
negative:
b = (b ^ %11111111) + 1 ' 2's complement to unsigned integer
x = 10*meantemp - (20*b*range/255)
TimeSlotDone:
setpoint = x

HTH
BrianT