Remote temperature sensor

[x3.exe]

Hi everyone,

I have a question about interfacing a temperature sensor to microcontroller, which is 5m away from the sensor. There are a couple of things that I want to find out:

1) How would this separation between the uC and the sensor affect the acuuracy of readings? If the sensor's gain is 10mV/C, than voltage drop across the cable could result in significant error.
2) Are there any methods that could reduce this error.
3) What type of temperature sensor should I use for this purpose?

Looking forward to your replies, Thanx in advance.

 

[pakitos]

there should be no problem any way you can amplify the signal and then send the result
about the sensor a simple lm35 or LM 335 will do the work. It you need the answer in degree C kelvin or F? although you are using MC better to get result in the unit you need

 

[karesz]

Hi x3exe,
Thes is depend on your senors type.
Use a supply line extra & signal & GND in a shielded cable.
But if you have thermo cross/element_is some others to do...
In all cases for better precision are 3/or 4 wire (Kelvin connection) solutions to apply.
K.

 

[Tahmid]

Hi,
Take a look at DS1820.
It uses the one-wire protocol. Isn't too hard too implement with mikroC/mikroBASIC.
It can be used upto 300 metres.
Hope this helped.
Tahmid.

Added after 2 minutes:

I have a code written in mikroBASIC and ATmega88. If you want, I can post it.
Tahmid.

 

[x3.exe]

Thank you all for your replies, they were really helpful.

Tahmid, DS1820 seems to be perfectly suitable for my application. I would appreciate if you could send me the code for interfacing it to uC.

Tnanx in advance.

 

[Tahmid]

Hi,
Here is the code in mikroBASIC for ATmega88 microcontroller.

program Temp_DS1820

'Microcontroller: ATmega88 (Atmel AVR)
'Programming Language: BASIC
'Compiler: mikroBASIC PRO for AVR v2.10
'Sensor: DS18S20
'Programmer: Tahmid

dim LCD_RS as sbit at PORTB2_bit
dim LCD_EN as sbit at PORTB3_bit
dim LCD_D4 as sbit at PORTB4_bit
dim LCD_D5 as sbit at PORTB5_bit
dim LCD_D6 as sbit at PORTB6_bit
dim LCD_D7 as sbit at PORTB7_bit

dim LCD_RS_Direction as sbit at DDB2_bit
dim LCD_EN_Direction as sbit at DDB3_bit
dim LCD_D4_Direction as sbit at DDB4_bit
dim LCD_D5_Direction as sbit at DDB5_bit
dim LCD_D6_Direction as sbit at DDB6_bit
dim LCD_D7_Direction as sbit at DDB7_bit


sub procedure ConversionDelay()
    delay_ms(800)
end sub

sub procedure StabilizeDelay()
    delay_ms(200)
end sub

dim Temperature as word
dim TempH as byte
dim TempL as byte
dim TLow as byte
dim vDisp as string[9]
dim DecimalPoint as byte

main:
     DDRC = $FE 'RC0 input for One-Wire
     LCD_Init()
     LCD_Cmd(_LCD_CURSOR_OFF) 'LCD Cursor off
     LCD_Cmd(_LCD_CLEAR) 'Clear LCD
     StabilizeDelay() 'Wait for sensor and LCD to stabilize
     vDisp = "+124.5 'C"
     LCD_Out(1, 1, "Temp:")
     while true
         OW_Reset(PORTC, 0) 'Reset command to initialize One-Wire
         OW_Write(PORTC, 0, $CC) 'Skip ROM Command
         OW_Write(PORTC, 0, $44) 'Convert_T command
         ConversionDelay() 'Provide delay for conversion
         OW_Reset(PORTC, 0) 'Reset command to initialize One-Wire
         OW_Write(PORTC, 0, $CC) 'Skip ROM Command
         OW_Write(PORTC, 0, $BE) 'Read Scratchpad Command
         Temperature = OW_Read(PORTC, 0) 'Read Temperature low byte
         Temperature = Temperature + ((OW_Read(PORTC, 0)) << 8) 'Read Temperature high byte and convert low and high bytes to 16-bit
         TempH = Hi(Temperature) 'High 8 bits of Temperature
         TempL = Lo(Temperature) 'Low 8 bits of Temperature
         DecimalPoint = Temperature.B0 'Check if Temperature is integer or fractional
         if (Temperature and $8000) then 'If reading is negative
            vDisp[0] = "-"
            TempL = byte((not TempL + 1) >> 1)
         else 'If reading is positive
            vDisp[0] = "+"
            TempL = TempL >> 1 'Shift one position right (divide by 2) to get integer reading and get rid of decimal point
         end if
         vDisp[1] = TempL div 100 + 48 'Get hundreds and convert to ASCII
         vDisp[2] = (TempL div 10) mod 10 + 48 'Get tens and convert to ASCII
         vDisp[3] = TempL mod 10 + 48 'Get units and convert to ASCII
         if (DecimalPoint) then 'If reading is fractional, ie has 0.5 at end
            vDisp[5] = "5"
         else 'If reading is a whole number
            vDisp[5] = "0"
         end if
         LCD_Out(1, 8, vDisp) 'Show temperature
     wend
end.

Fuse bit settings:
   SUT1 = 0(PROGRAMMED)
   CKSEL3 = 0(PROGRAMMED)
   CKSEL2 = 0(PROGRAMMED)
   CKSEL0 = 0(PROGRAMMED)
   SPIEN = 0(PROGRAMMED)
   Everything else = 1(UNPROGRAMMED)

Hope this helps.
Tahmid.