I'm finishing up a refrigerator/freezer control, logging, display and statistics project using the DS18B20 as my sensors. The way this chip handles crossing zero is problematic for simpletons like me. To save a new minimum temperature requires code like this:
Fairly nasty stuff...
So I hit on the idea of rescaling the DS18B20 output to get a linear progression of numbers. The rescale code looks like this:
Now saving a new minimum looks like this:
WHEW! That is easier. Imagine how much easier the compressor cut in and cut out code would be! (I never even tried...)
The DS18B20 output, rescale and temperature conversions work out like this:
Conversions work like this:
The above two code samples are designed to be copied and pasted into the PICAXE Program Editor and then run in Simulate. These also demonstrate a fairly slick (to me) way of passing variables to a sub procedure.
What do you all think?
Was there a much easier way to do this that I missed?
Code:
if RCTemp<128 AND Rmin<128 then
if RCTemp < Rmin then
Rmin = RCTemp
end if
elseif RCTemp>127 AND Rmin>127 then
if RCTemp > Rmin then
Rmin = RCTemp
end if
elseif RCTemp<128 AND Rmin>127 then
'temp>0 min<0 DO NOTHING!
elseif RCTemp>127 AND Rmin<128 then
if RCTemp > Rmin then
Rmin = RCTemp
end if
end ifSo I hit on the idea of rescaling the DS18B20 output to get a linear progression of numbers. The rescale code looks like this:
Code:
if RCTemp < 127 then
RCTemp = RCTemp + 100
else
RCTemp = 128 - RCTemp + 100
end if
Code:
if RCtemp < Rmin then
Rmin = RCtemp
end ifThe DS18B20 output, rescale and temperature conversions work out like this:
Code:
DS18B20 Rescale C F
------- ------- --- ---
10 110 10 50
9 109 9 48
8 108 8 46
7 107 7 45
6 106 6 43
5 105 5 41
4 104 4 39
3 103 3 37
2 102 2 36
1 101 1 34
0 100 0 32
129 99 -1 30
130 98 -2 28
131 97 -3 27
132 96 -4 25
133 95 -5 23
134 94 -6 21
135 93 -7 19
136 92 -8 18
137 91 -9 16
138 90 -10 14
139 89 -11 12
140 88 -12 10
141 87 -13 9
142 86 -14 7
143 85 -15 5
144 84 -16 3
145 83 -17 1
146 82 -18 0
147 81 -19 -2
148 80 -20 -4
149 79 -21 -6
150 78 -22 -8
151 77 -23 -9
152 76 -24 -11
153 75 -25 -13
Code:
'convert RESCALED whole number temperature values from READTEMP to Celsius
SYMBOL Temp = b0
SYMBOL Sign = b1
Main:
sertxd ("Enter RESCALED DS18B20 value", cr,lf)
Serin C.1,N9600_8,Temp
ptr = 0
@ptr = Temp
if Temp > 44 AND Temp < 226 then
gosub RescaledDS18B20toC
ptr = 0
Temp = @ptr
ptr = 1
Sign = @ptr
SERTXD (Sign, #Temp,"C", cr, lf)
else
SERTXD ("Values must be above 44 and below 226", cr, lf)
end if
GOTO Main
RescaledDS18B20toC:
if @ptr = 100 then '0C
ptr = 1
@ptr = " "
ptr = 0
@ptr = 0
else if @ptr < 100 then 'below 0C
ptr = 1
@ptr = "-"
ptr = 0
@ptr = 100 - @ptr
else 'above 0C
ptr = 1
@ptr = "+"
ptr = 0
@ptr = @ptr - 100
endif
Return
Code:
'convert RESCALED whole number temperature values from READTEMP to Fahrenheit
'mostly stolen from marks and ehow.com
'www.ehow.com/how_7414093_convert-negative-celsius-fahrenheit.html
SYMBOL Temp = b0
SYMBOL Sign = b1
Main:
sertxd ("Enter RESCALED DS18B20 value", cr,lf)
Serin C.1,N9600_8,Temp
ptr = 0
@ptr = Temp
if Temp > 44 AND Temp < 226 then
gosub RescaledDS18B20toF
ptr = 0
Temp = @ptr
ptr = 1
Sign = @ptr
SERTXD (Sign, #Temp,"F", cr, lf)
else
SERTXD ("Values must be above 44 and below 226", cr, lf)
end if
GOTO Main
RescaledDS18B20toF:
if @ptr = 82 then '0F
ptr = 1
@ptr = " "
ptr = 0
@ptr = 0
else if @ptr < 82 then 'below 0F
ptr = 1
@ptr = "-"
ptr = 0
@ptr = @ptr * 9 / 5
@ptr = 148 - @ptr
else 'above 0F
ptr = 1
@ptr = "+"
ptr = 0
@ptr = @ptr * 9 / 5
@ptr = @ptr - 148
endif
ReturnWhat do you all think?
Was there a much easier way to do this that I missed?