DS1820 versus DS18S20

[Darrel Taylor]

I think it's beacuse i'm using the DS18S20P. Can somebody confirm this?

I think that means it uses "Parasitic Power" only.

If so, you have to drive the DQ line HIGH for 750ms during the conversion.
After that you can read it like normal.
It doesn't get power from the VDD pin.

[biggej]

DT is on the right track but maybe for not exactly the right reason. The DS18S20 does not have to run with parisitic power but it can if needed. However this from Maxim..
"Specification Differences: The primary specification difference between the two parts is the temperature conversion time: DS1820 = 500ms (max) and DS18S20 = 750ms (max)."

I believe you may also be using "count remain" improperly to signal the end of conversion. End of conversiion may be determined by issing a "Read time slot" command until the result is non zero. (Yes, it is in the data sheet!) All that being said, you can probably get by with only adding the 750ms delay after the conversion command.
Jim

[Darrel Taylor]

DT is on the right track but maybe for not exactly the right reason. The DS18S20 does not have to run with parisitic power but it can if needed.

The DS18S20 doesn't, but the DS18S20P also called DS18S20-PAR, only uses "Parasitic Power".

The datasheet ...
http://datasheets.maxim-ic.com/en/ds/DS18S20-PAR.pdf

[biggej]

I should have know Darrel had it right!
It will take a wiring change to make Parasitic Power work too.
Jim

[Bill Legge]

Thought the following code might interest someone?
It's based on the code for the DS18B20 by Bruce on the Reynolds/Renton web site.

The chip I used is the DS18B20-PAR ( the device is marked 'DS18B20P') and will only work with parasitic power. Achieved by using an 2N7000 MOSFET (gate on PORTC.1, source on the DQ line and the drain on +5 supply).

The DQ line must be driven high within 10uS of the 'convert' command and maintained for the duration of the conversion (750mS for 12 bit conversion).

The extra code to do this follows the conver command.

' -----[ Title ]-----------------------------------------------------
'
' File...... WVL Water Remote
' Purpose... Remote station for control of water heater
' Date...... June 2010
'
' 7. DS18B20P measures tank temp. Parasitic power only with DQ pulled hard
'    high after 'read temp' command by MOSFET 2N7000 with gate on PORTC.1

' 8. The DS18B20P range +125C to -55C

' 9. The DQ line must be high for the conversion period. Periods and resolution:
'       9  bit   93.7mS     0.5C        1/2  degree
'       10 bit  187.5mS     0.25C       1/4  degree
'       11 bit  375.0mS     0.125C      1/8  degree
'       12 bit  750.0mS     0.0625C     1/16 degree
'    12 bit resolution used so conversion delay is 750mS and conversion factor is
'    625 that gives temperature in 1/10000 degrees C

' 10. The code is based on the DS18B20 pages at web site REYNOLDS/RENTON
'
' ----[ Includes / Defines ]-------------------------------------------
'
clear
define OSC 20				' Use HSPLL during compilation
DEFINE LCD_DREG	PORTB	    ' Define PIC port used for LCD Data lines
DEFINE LCD_DBIT	4		    ' Define first pin of connected to LCD
DEFINE LCD_RSREG PORTB	    ' Define PIC port used for RS line of LCD
DEFINE LCD_RSBIT 2		    ' Define pin used for RS connection
DEFINE LCD_EREG	PORTB   	' Define PIC port used for E line of LCD
DEFINE LCD_EBIT	1		    ' Define pin used for E connection
define LCD_RWREG PORTB      ' Define PIC port used for RW
DEFINE LCD_RWBIT 3          ' Define pin used for RW
DEFINE LCD_BITS	4		    ' Define 4 bit communication mode to LCD
DEFINE LCD_LINES 4		    ' Define using a X line LCD
DEFINE LCD_COMMANDUS 1500	' Define delay time between sending LCD commands
DEFINE LCD_DATAUS 44	    ' Define delay time between data sent
FLAGS=0
include "modedefs.bas"      ' Include serout defines
'
' ----[ Variables ]----------------------------------------------------
'
TempR       VAR word        ' DS18B20P reading. raw data
TempC       VAR WORD        ' Temp in deg C
Float       VAR WORD        ' Holds remainder for + temp C display

Heartbeat	var	PORTA.0		' Heartbeat each cycle

DQ          var PORTC.0     ' DS18B20P. Comms
Pullup      var PORTC.1     ' DS18B20P
'
' -----[ Initialization - PIC ]--------------------------------------
'
ADCON1	= %00000110			' All ports digital
CMCON	= %00000111			' Comparators off. Essential or PORTF won't work
'
' -----[ Identify ]--------------------------------------------------
'
LCDOUT $fe,$80,"Water Heater"
pause 1000
LCDOUT $fe,1
'
' *****************************************************************************
' *                                                                           *
' *                         M A I N   P R O G R A M                           *
' *                                                                           *
' *****************************************************************************
									    
Main:	
    GOSUB Get_temp
    LCDOUT $fe,$c0,"Temp  : ",DEC TempC,".",DEC Float
		
	toggle Heartbeat
    pause 1000	
	goto Main	
	
' *****************************************************************************
' *                                                                           *
' *                         S U B R O U T I N E S                             *
' *                                                                           *
' *****************************************************************************


Get_temp: 
    OWOUT   DQ,1,[$CC, $44]         ' Skip ROM search & do temp conversion
    high Pullup                     ' Turns MOSFET on to make DQ line high
    pause 750                       ' Conversion time for 12 bit reading
    low Pullup                      ' Turn MOSFET off after read temp command     

    OWOUT   DQ,1,[$CC, $BE]         ' Skip ROM search & read scratchpad memory
    OWIN    DQ,2,[TempR.Lowbyte,TempR.Highbyte]' Read two bytes / end comms

Convert_Temp:
    TempC = DIV32 10                        ' Use Div32 value to calculate precise deg C
    TempC = (TempR & $0FF0) >> 4            ' Mask middle 8-bits, shift into lower byte
    Float = ((TempR.Lowbyte & $0F) * 625)   ' Lower 4-bits of result * 625
  
    RETURN

END

The MCU is an PIC16F877A running at 20MHz.

Regards Bill Legge

[gadelhas]

Hi,

Thanks to everyone,

I i'll try the code and circuit that Bill Legge posted.

Regards
Gadelhas

[barcosta]

hi im elie,im doing my final project :temperature regulator system
im newer in the picbasic pro
i need to know a code t read the tempeature from the sensor ds1820
thank you all for your replys