[SOLVED] Pic18 Interfacing with LM35DZ

Praveen Kumar P S · Oct 8, 2014

Hello guys....
I wanted to interface my Lm35 with pic18f4550...

here is my code::

Code:

#include <18f4550.h>
#device ADC=10
#fuses XT, HS, NOWDT, NOPROTECT, BROWNOUT, NOLVP, PUT 
#use delay(clock=48000000)
//#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7,ERRORS)
#include<flex_lcd216.c>

void main()
{
float32 T , val;
delay_ms(500);
lcd_init();
lcd_setcursor_vb(1,1);
printf(lcd_putc,"\f ");
setup_adc_ports(AN0);
setup_adc(ADC_CLOCK_INTERNAL); 
for(;;)
{
set_adc_channel(0);
delay_ms(2);
T=read_adc();
delay_ms(10);
val=T*20*(5/1023);
lcd_gotoxy(1,1);
delay_ms(10);
printf(lcd_putc,"Adc Read:%3.2f ",T);
lcd_gotoxy(1,2);
delay_ms(10);
printf(lcd_putc,"Tem Read:%3.2f \xDFC",val);
delay_ms(500);
output_toggle(PIN_D1);
delay_ms(10);
output_toggle(PIN_E1);
delay_ms(10);
}

}

The output i got in my lcd is

Adc Read:87.00
Tem Read:0.00 C

i dont know why is it giving 0.00 ...plz help..

Thank You...

milan.rajik · Oct 8, 2014

Please Zip and post complete CCS C project files so that the code can be compiled and tested.

Praveen Kumar P S · Oct 8, 2014

milan.rajik said:
Please Zip and post complete CCS C project files so that the code can be compiled and tested.

Thanks for the quick replay milan...
Here is my whole project:::

Thank You....

milan.rajik · Oct 8, 2014

Please Zip and post flex_lcd216.c file. I can't compile without that file

ashad · Oct 8, 2014

Code:

delay_ms(10);
val=T*20*(5/1023);
lcd_gotoxy(1,1);

change above lines with val= (T*5)/1000;
May solve ur problem

milan.rajik · Oct 8, 2014

I changed the code a little and compiled for 20 MHz and it worked. If you use 48 MHz crystal or HSPLL then you need to adjust delay_cycles() in the flex_lcd216.c file. Increase the delay and it will work fine. Instead of

Code C - [expand]
1
delay_cycles() use delay_us(500).

Praveen Kumar P S · Oct 8, 2014

milan.rajik said:
Please Zip and post flex_lcd216.c file. I can't compile without that file

Sorry for that....

Here is my lcd driver::
Thank You...

- - - Updated - - -

milan.rajik said:
I changed the code a little and compiled for 20 MHz and it worked. If you use 48 MHz crystal or HSPLL then you need to adjust delay_cycles() in the flex_lcd216.c file. Increase the delay and it will work fine. Instead of

Code C - [expand]
1
delay_cycles() use delay_us(500).

thanks for replay....
I tried to run the code with 20Mhz...but still not working..Every thing is working fine except Temp Read...it is still 0.00
Thank you..

- - - Updated - - -

ashad said:
Code:

delay_ms(10); val=T*20*(5/1023); lcd_gotoxy(1,1);

change above lines with val= (T*5)/1000;
May solve ur problem

Thanks for the replay..

I did what you have said..but still no effect....

Thank you...

milan.rajik · Oct 8, 2014

Post your circuit.

I changed the delays in flex_lcd216.c file and it worked in Proteus 8.1. If it still doesn't work then increase the delays. I compiled for 48 MHz.

paulfjujo · Oct 8, 2014

hello,

What is the ref for ADC , is it 5V as +Vref and -Vref=0
so, you get 205 points for 100 °C
calculus becomes
Temp= ReadADC*100/205;

if you can use +4.096V for +VRef
you will get 250 points for 100°C
so more easy
Temp=ReadADC* 100/250;
or Temp= ReadADC *0.4;

or without floating point use:
Temp as an integer value.
Temp=ReadADc*40;
result is ! 87*40=3480
place the decimal point after the 2 first digits..

Praveen Kumar P S · Oct 8, 2014

milan.rajik said:
Post your circuit.

I changed the delays in flex_lcd216.c file and it worked in Proteus 8.1. If it still doesn't work then increase the delays. I compiled for 48 MHz.

Hey milan .....

Finally it worked....i give a 500ms delay after all equation part as you said...it worked...
now it shows the Temp read...but now its not showing the correect temp...

Thank You

- - - Updated - - -

paulfjujo said:
hello,

What is the ref for ADC , is it 5V as +Vref and -Vref=0
so, you get 205 points for 100 °C
calculus becomes
Temp= ReadADC*100/205;

if you can use +4.096V for +VRef
you will get 250 points for 100°C
so more easy
Temp=ReadADC* 100/250;
or Temp= ReadADC *0.4;

or without floating point use:
Temp as an integer value.
Temp=ReadADc*40;
result is ! 87*40=3480
place the decimal point after the 2 first digits..

Hi paul....
I have not given any Vref...Are u saying that i should give a 5v supply to +vref pin directly....and what should be the current rating for it???

Thank You

paulfjujo · Oct 8, 2014

No, it is internaly connected to Vdd (+5V) by default config..
Except if you want to use external +VRef ( it is RAx pin ) as a voltage reference of 4.01V

you get 87 points , is the ambiant temperature around 34°C ?

milan.rajik · Oct 8, 2014

Use my code. It shows the correct value for Temperature. You don't have to give 5V to Vref+ pin as you have not enabled Vref+ pin. 500 ms delay is too much. Try using 30 ms delay and see if it works.

Praveen Kumar P S · Oct 8, 2014

milan.rajik said:
Use my code. It shows the correct value for Temperature. You don't have to give 5V to Vref+ pin as you have not enabled Vref+ pin. 500 ms delay is too much. Try using 30 ms delay and see if it works.

Hey milan,
Its working with 30ms delay....but the problem is my calculation,i suppose..Lm35dz will vary by 1 deg cel/10 mV..
but i m geting adc read between 80 and 90...i.e for 85 adc value i have a temprature of 8.5 deg cel... :-?

help me plz...
Thank you..

- - - Updated - - -

paulfjujo said:
No, it is internaly connected to Vdd (+5V) by default config..
Except if you want to use external +VRef ( it is RAx pin ) as a voltage reference of 4.01V

you get 87 points , is the ambiant temperature around 34°C ?

i m trying to use the internal vref...actually i didnt get what you said....i dont know how to calculate the points....
also i have this strange doubt..that i have given supply of 3.6V to Pic...so my internal Vref may be 3.6V..not 5V.correct...??

Thank You..

milan.rajik · Oct 8, 2014

Did you try my code ? Try my code in while(1) loop.

- - - Updated - - -

Read this and configure fuses properly. https://www.mikroe.com/forum/viewtopic.php?t=10646

Try attached .hex file with a 4 MHz crystal and reply.

- - - Updated - - -

Test also this .hex file which is compiled for 20 MHz crystal.

also i have this strange doubt..that i have given supply of 3.6V to Pic...so my internal Vref may be 3.6V..not 5V.correct...??

Yes, Internal Vref+ will be VDD. If you have given 3.6V as VDD then 3.6V will represent 1023 raw adc value.

Provide 5V VDD and use below fuses and a 20 MHz Crystal.

Code C - [expand]
1
#fuses HS, PLL5, CPUDIV1, NOWDT, NOPROTECT, BROWNOUT, NOLVP, PUT, NOMCLR

Try rev1 code with 20 MHz crystal and 3.6V VDD.

paulfjujo · Oct 9, 2014

hello,

but the problem is my calculation,i suppose..Lm35dz will vary by 1 deg cel/10 mV..
but i m geting adc read between 80 and 90...i.e for 85 adc value i have a temprature of 8.5 deg cel...

you are mixing points and mV.

ADC read gives points as result ..in your case, with +Vref=internal Vdd=3,6V
1023 pts for 3,6V or 3600mV
this full scale 3600mV represente 360°C or 1023 pts
so scaling is : Temp(°C)= ADC reading (Pts) *360/1023
if ADC read 85 pts => 85*360/1023=> 29.9°C

Praveen Kumar P S · Oct 10, 2014

milan.rajik said:
Did you try my code ? Try my code in while(1) loop.

- - - Updated - - -

Read this and configure fuses properly. https://www.mikroe.com/forum/viewtopic.php?t=10646

Try attached .hex file with a 4 MHz crystal and reply.

- - - Updated - - -

Test also this .hex file which is compiled for 20 MHz crystal.

Yes, Internal Vref+ will be VDD. If you have given 3.6V as VDD then 3.6V will represent 1023 raw adc value.

Provide 5V VDD and use below fuses and a 20 MHz Crystal.

Code C - [expand]
1
#fuses HS, PLL5, CPUDIV1, NOWDT, NOPROTECT, BROWNOUT, NOLVP, PUT, NOMCLR

Try rev1 code with 20 MHz crystal and 3.6V VDD.

Hey milan
sorry for the late replay .
i tried your code...and it is working very well...
But i didnt understand the following code

Code:

 setup_adc_ports(AN0 | VSS_VDD)

and

Code:

 T = T / 2.84167;  //2.046;

AN0|VSS_VDD----> Is it for directly using internal Vref...
and
2.84167----->why is this used?

Thank You...

- - - Updated - - -

paulfjujo said:
hello,

you are mixing points and mV.

ADC read gives points as result ..in your case, with +Vref=internal Vdd=3,6V
1023 pts for 3,6V or 3600mV
this full scale 3600mV represente 360°C or 1023 pts
so scaling is : Temp(°C)= ADC reading (Pts) *360/1023
if ADC read 85 pts => 85*360/1023=> 29.9°C

Hey paul

I understand the logic completely...
Is there any way to use the internal Vref with the help of software..i mean without specifying Vref=3.6

Thank You...

Venkadesh_M · Oct 11, 2014

not possible. but you can give constant voltage in vref pin with a zener.

milan.rajik · Oct 11, 2014

AN0|VSS_VDD----> Is it for directly using internal Vref...

Yes, It is for using VSS and VDD as Vref- and Vref+ but it is optional. You can use just AN0. It is mentioned in your device header file.

2.84167----->why is this used?

5V = 1023 = x
1.5V = 306.9 = 150 deg C

x = 1023 * 150 / 306.9 = 500

You can use temp = adcVal * 500 / 1023

500 / 1023 = 0.4887585532746823

adcVal * 500 / 1023 can be replaced by 0.4887585532746823 or

1 / 2.046 (1/0.4887585532746823 = 2.046)

I was getting 308 instead of 306.9 as raw adc value for 150 deg C, so to adjust I used 2.84167.

Praveen Kumar P S · Oct 11, 2014

Hello milan....

5V = 1023 = x
1.5V = 306.9 = 150 deg C

x = 1023 * 150 / 306.9 = 500

You can use temp = adcVal * 500 / 1023

500 / 1023 = 0.4887585532746823

adcVal * 500 / 1023 can be replaced by 0.4887585532746823 or

1 / 2.046 (1/0.4887585532746823 = 2.046)

I was getting 308 instead of 306.9 as raw adc value for 150 deg C, so to adjust I used 2.84167.

I understand This clearly.........

but i didnt understand..

Code:

setup_adc_ports(AN0 | VSS_VDD);

if VSS and VDD can be used as Vref- and vref+ can we use

Temp=adc_read*100*(Vref+/1023);

Also venkadesh_M is saying that we cant use the internal Vref directly with the help of software..for that we have to use Vref pins....If it is so how to use Vref Pins?

Also i m new to ccs c compiler and pic..sorry for asking noob questions...
could u plz suggest me a good book for ccs c compiler...i have the ccs c manual...but it is not well enough...

Thank u...

milan.rajik · Oct 11, 2014

ould u plz suggest me a good book for ccs c compiler

Embedded C Programming and the Microchip PIC by Barnett, O'Cull, Cox and of course CCS C Compiler Manual.

If you use AN) or AN0 | VSS_VDD they both are same. It will use Internal Vref- and Vref+ which is your VSS and VDD. You can use just AN0. The | VSS_VDD is optional. Default is VSS will be Vref- and VDD will be Vref+.

Just use the right equation to get temperature value from raw adc value.

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