ds1820 error

[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.
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[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.
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[CrazyCooter]

ok have got it to work. i replaced the 4k7 resistor with a 2k4 resistor and rererererereread the data sheet for the ds1820 and put a pause 750 after the start temp conversion. IE.
OWOUT DQ,1, [$CC, $44]
PAUSE 750 ' Max conversion time
OWIN DQ, 4, [count_remain]

i found it on pg 20 under AC Electrical Characteristics temperature conversion time

i found its not as fast as i would have thought. is there any other way to make it faster or is this the speed of using the 1 wire devices

the code

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, 1, [$CC, $44] ' Start temperature conversion
pause 750 'NEEDED FOR TEMP STABILIZING
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)," C"

GoTo mainloop ' Do it forever
end

thanks

crazy cooter

[Darrel Taylor]

Hmmm, something doesn't seem right.

The lower value pull-up, and pause 750 shouldn't be needed.
The OWIn DQ, 4, [count_remain] will check the busy bit until the conversion is complete.

..... Unless it's running on "Parasite Power". In which case you need a Strong Pull-up on DQ during the conversion, and you can't read from the device for 750ms.

If that fixed your problem, then you probably don't have 5V on pin 3 of the 1820.
And if "Parasite Power" was intentional, you may need to do things differently.
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