ds1820 error

[CrazyCooter]

hi all. think i got the correct spot. i am having a issue with the dallas ds1820 temp sensor. i know it has been written many times. but think this is a different issue. i keep getting the same temp (85.00 deg c) even when i put the hair drier on it. is it stuffed????????

my code for a 16f88 internal osc set at 4 mhz

OSCCON = %01101000 'INTRC = 4 MHz
TRISA = %11111111
ANSEL = 0 'DISABLE ALL ADC
CMCON = 7 'DISABLE ALL ANALOG COMPARATOR
WHILE OSCCON.2=0:WEND 'STABILISE THE CLOCK
ADCON1 = 1
DEFINE OSC 4
PAUSE 1000
DEFINE LCD_DREG PORTB
DEFINE LCD_DBIT 4 '4,5,6,7
DEFINE LCD_RSREG PORTB
DEFINE LCD_RSBIT 3
DEFINE LCD_EREG PORTB
DEFINE LCD_EBIT 2
DEFINE LCD_BITS 4
DEFINE LCD_LINES 2
DEFINE LCD_COMMANDUS 2000
DEFINE LCD_DATAUS 50
pause 1000
lcdout $fe, 1

' One-wire temperature for DS18S20

' This program must be compiled with PBP version 2.40 or later


temperature VAR WORD ' Temperature storage
count_remain VAR BYTE ' Count remaining
count_per_c VAR BYTE ' Count per degree C

DQ VAR PORTA.1 ' One-wire data pin


mainloop: OWOUT DQ, 0, [$B4] ' READ POWER SUPPLY
OWOut DQ, 1, [$CC, $44] ' Start temperature conversion

waitloop: OWIn DQ, 4, [count_remain] ' Check for still busy converting
IF count_remain = 0 Then waitloop

OWOut DQ, 1, [$CC, $BE] ' Read the temperature
OWIn DQ, 0, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

' Calculate temperature in degrees C to 2 decimal places (not valid for negative temperature)
temperature = (((temperature >> 1) * 100) - 25) + (((count_per_c - count_remain) * 100) / count_per_c)
LCDOut $fe, 1, DEC (temperature / 100), ".", DEC2 temperature, " C"

' Calculate temperature in degrees F to 2 decimal places (not valid for negative temperature)
temperature = (temperature */ 461) + 3200
LCDOut $fe, $c0, DEC (temperature / 100), ".", DEC2 temperature, " F"

Pause 500 ' Display about once a second
LCDOUT $FE, 1, "DALLAS DS1820"
PAUSE 1000
GoTo mainloop ' Do it forever


any ideas of maybe where i went wrong

thanks

crazy cooter

[Darrel Taylor]

The fact that you're getting 85°C is a good sign.

That's the power-on default for the temperature registers of the DS1820. So at least you know the hardware is working.

My guess is that the "READ POWER SUPPLY" line is not allowing the "start conversion" to work. Try it with that line commented out.
<br>

[CrazyCooter]

i have tried it without the READ POWER SUPPLY. I have also tied a 4.7k resistor from the DQ line to 5V. Am i initialising it correctly??? This was a direct copy from melabs using "onewire.bas"

[james]

Did you set internal osc?

Right after you compile, the screen comes up to program the chip. if you click view -> configuration. You can set INTOSC.

a place I've tripped up before, just a thought.

hope it helps

[Bruce]

Try changing this;
OWIn DQ, 0, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

to this;
OWIn DQ, 2, [temperature.LOWBYTE, temperature.HIGHBYTE, Skip 4, count_remain, count_per_c]

I beleive you need mode 2 after the last read to issue the reset pulse so the sensor
is ready for the next on return to the start of your program.

[Darrel Taylor]

I had to try it out, but all I have is a DS18B20.

The original code worked fine, except I had to change the formula. But the communications seems OK.
<br>

[CrazyCooter]

Thanks To Everyone Who Gave Me Advice Here. It Ended Up Being Two Dead Ds18s20. I Got Some New Ones Now And Its All Working Well.


Regards

Crazy Cooter