LM35 Temp and Pseudocode help wanted

[Jeff]

I can blink a few leds, now I would like to try to turn on an led when my LM35 temp sensor reaches about 80 degrees F (27C), eventually running it out serially to a display.
I have a few questions about digitizing the analog signal. I am in the process of setting up the AN registers. I was going to use the internal Vref but not sure how to do it. Datasheet gives option (p43) for vdd or Vref pin. It is shown disconnected on my schematic. How do I scale this? The LM gives 10mv/degreeC (21 = 210mV = 69.8F about ROOM TEMP) Is there another way to calibrate it? Do I need to put a reference voltage on this pin?? I am including what I have so far- far from complete - just getting things configured. I am having a hard time writing the pseudocode especially with the above info missing. I guess what I want to do is:
set up an
set up digital output
read an input
compare it to vref
if vref register<AN input, scan again
if vref register>AN input, change states of GPIO2
maintain this state while scanning again

http://ww1.microchip.com/downloads/en/devicedoc/41190c.pdf



SYMBOL ANSEL = $9F 'SET TO AI, NOT DI
'SET OSC - p44 DATASHEET

SYMBOL ADCON0 = $1F 'SET PIN0 TO ANALOG IN p43
'TURN ON AD
'START AD
'SET CHAN AN0
'VREF PIN ???????????????
'LH JUSTIFIED
SYMBOL CMCON = $19 '001 ON/OFF COMPARE MODULE. BIT6 IS STATUS CHANGE FLAG P37
symbol VRCON = $99 'INTERNAL VREF CTRL REGISTER
'================================================= ==============================
POKE ANSEL,%00011111 'SEE ABOVE
POKE ADCON0,%01100011 'SEE ABOVE
POKE CMCON,%01000001 'COMPARITOR CONTROL CONFIG
POKE VRCON,%01000111 'SET LOW RANGE
'CVREF ENABLE ????????????????
'================================================= ==============================
SYMBOL TRISA = $85 'IO ADDRESS DIRECTION
POKE TRISA,%00000011 'SET PIN0 AS INPUT – TEMP SENSOR
'SET PIN1 AS INPUT – VREF
'SET PIN2 AS OUTPUT
SYMBOL GPIO = $05 '
SYMBOL TEMPSENS_IN = B1 'BYTE VAR TO STORE ANALOG DATA
SYMBOL VREF = B2 'BYTE VAR TO STORE REF DATA
SYMBOL FAN_ON = BIT8 'SET BIT8 TO ENABLE FAN ON
'================================================= ==============================
SYMBOL TEMP_PIN = PIN0
SYMBOL VREF_PIN = PIN1
SYMBOL FAN_PIN = PIN2

Thanks for any help or kick in the right direction. Jeff

[b1arrk5]

Hi Jeff,
Go to this site,
http://www.rentron.com/PicBasic1.htm
scroll to the bottom, and read Bruce's great tutorial on precision temperature measurement. He is using a different version of the sensor that you are using, but he discusses the differences, shows how to set up the A/D registers and how to set up vref. You can spend hours on Bruce's website, he shares a lot of knowledge, and I'm certain you'll find what you need there.

Jerry

[Jeff]

Brilliant, I'll check it out! Thanks!