Tempurature using Dallas DS1621 (BASCOM)

Measures temperatures from -55°C to +125°C

Three LED's to indicate in what range the temparature is.

User definable thermostat with high and low settings

Output via a relay to control a heater element or a blower fan (or something else)

Power supply ......................4.5 to 5.5 VDC

Power consumption ...........15mA

This circuit uses a Dallas DS1621 temperature sensor which indicates the temparature of the device. The temperature sensor has an termal alarm output, which becomes high when the temperature of the device exceeds a user defined value. When the temperature drops below a user defined value, the alarm output becomes low. In this way any amonut of hysteresis can be programmed. The values are stored in a special register of the device that is nonvolatile. The signal of the alarm output is amplified by a BC557 PNP transistor, that drives a relay that can switch a heater element or a blower on or off. The temperature settings and readings are communicated to/from the device over a simple 2-wire serial interface. An ATMEL 90S2313 microcontroller controls the serial communication to/from the DS1621.The microcontroller also controls three LED, only one of the LED's is on when the temparature is within a certain range. The range of the temperature in which the LED's are on can be set by the user in the program code. The circuit needs to be powered by a 5V power supply, which can be obtained from a wall-wart.

CODE

' ***************************************************************************
' *
' * Title : Temperature indicator
' * Version : 1.0
' * Last Updated : 15.03.2003
' * Target : At90s2313
' * Author : r.meurs@planet.nl
' * Program code : BASCOM AVR
' * Hardware req. : Temperatue indicator board
' *
' *
' * Description
' * This application reads the temperature from an DS1621 temp. sensor
' * One of three LED's is on when the temperature is within a certain range.
' *
' ****************************************************************************

Dim Tempmsb As Byte
Dim Templsb As Byte
Dim L_on As Byte
Dim L_off As Byte
Dim Tl As Byte
Dim Th As Byte
Dim Confg As Byte
Dim Count As Byte
Dim Slope As Byte
Declare Sub Get_temp
Declare Sub Write_th
Declare Sub Write_tl

Config Portb = Output
Portb = 255
Config Sda = Portd.0
Config Scl = Portd.1

Cls
Cursor Off
Goto Main

Sub Write_th
I2cstart
I2cwbyte &H90
I2cwbyte &HA1
I2cwbyte L_on
I2cstop
End Sub Write_th
'--------------
Sub Write_tl
I2cstart
I2cwbyte &H90
I2cwbyte &HA2
I2cwbyte L_off
I2cstop
End Sub Write_tl
'--------------
'read TH
I2cstart
I2cwbyte &H90
I2cwbyte &HA1
I2cstop

I2cstart
I2cwbyte &H91
I2crbyte Th , Nack
I2cstop
'--------------
'read TL
I2cstart
I2cwbyte &H90
I2cwbyte &HA2
I2cstop

I2cstart
I2cwbyte &H91
I2crbyte Tl , Nack
I2cstop
'--------------
'read config
I2cstart
I2cwbyte &H90
I2cwbyte &HAC
I2cstop

I2cstart
I2cwbyte &H91
I2crbyte Confg , Nack
I2cstop
'--------------

'read counter
I2cstart
I2cwbyte &H90
I2cwbyte &HA8
I2cstop

I2cstart
I2cwbyte &H91
I2crbyte Count , Nack
I2cstop

'--------------

'read slope
I2cstart
I2cwbyte &H90
I2cwbyte &HA9
I2cstop

I2cstart
I2cwbyte &H91
I2crbyte Slope , Nack
I2cstop
'--------------

Sub Get_temp:
'start convert
I2cstart
I2cwbyte &H90
I2cwbyte &HEE
I2cstop
'-------------
'read temperature
I2cstart
I2cwbyte &H90
I2cwbyte &HAA
I2cstop

I2cstart
I2cwbyte &H91
I2crbyte Tempmsb , Ack
I2crbyte Templsb , Nack
I2cstop
'read config
I2cstart
I2cwbyte &H90
I2cwbyte &HAC
I2cstop

I2cstart
I2cwbyte &H91
I2crbyte Confg , Nack
I2cstop
End Sub Get_temp
'--------------

Main:

L_on = 25 'if Temp > 25 the load will be switched on
L_off = 20 'if Temp < 20 the load will be switched off
Gosub Write_th
Gosub Write_tl

Loop:

Wait 1

Gosub Get_temp

Select Case Tempmsb

Case Is < 21 : Portb = &B00000001 'if Temp <21 then the yellow LED is on
Case 21 To 25 : Portb = &B00000010 'if Temp is between 21 and 25 then the green LED is on
Case Is > 25 : Portb = &B00000100 'if Temp >25 then the red LED is on

End Select

Goto Loop