DS2760 module

rePete

Hi,

A propeller newbie here...

I'm getting to know the propeller with some baby steps. Right now I'm trying to read the output from the DS2760 TC module and am hoping somebody can point me in the right direction.

Very simple code but don't seem to be getting the correct results

CON

_clkmode = xtal1 + pll16x
_xinfreq = 5_000_000


OBJ

debug : "FullDuplexSerialPlus"
ow : "OneWire"


PUB TwoWayCom | a, b, c, tc_volt1, tc_volt2, tc_volt

ow.start(15) ' DS2760 on pin 15
debug.start(31, 30, 0, 57600)

repeat
ow.reset
ow.writeByte($CC)
ow.writeByte($69)
ow.writeByte($18)
a := ow.readByte
b := ow.readByte
debug.dec(c)
debug.str(string(" "))
debug.dec(a)
debug.str(string(" "))
debug.dec(b)
debug.str(string(10,13))

ow.writeByte($CC)
ow.writeByte($69)
ow.writeByte($0E)

tc_volt.byte[noparse][[/noparse] 0]:=ow.readByte
tc_volt.byte[noparse][[/noparse] 1]:=ow.readByte

' tc_volt:=tc_volt >> 3
' tc_volt:=tc_volt/4000
debug.dec(tc_volt)
debug.str(string(" "))
debug.dec(tc_volt.byte[noparse][[/noparse] 0])
debug. str(string(" "))
debug.dec(tc_volt.byte[noparse][[/noparse] 1])
debug.str(string(10,13))
waitcnt(clkfreq + cnt)



The ambient temperature seems to come out OK -> 19 C
I the tc voltage comes out off scale high...

431 18 224
65535 255 255

Help?

-Pete

lyons5959

I haved worked with this module on another project and found the same. The problem is caused because of the way a thermocouple works. The high numbers you are seeing are actually negative numbers meaning that the thermocouple junction is actually cooler than the chip itself. Try pinching the tip of the thermocouple between your fingers, it should read atleast a positive voltage, though probably not that high.

rePete

Thanks Lyons,

I hit the TC with a butane torch (buhuhahahaha) and still nothing [noparse]:([/noparse]

Was just thinking that maybe I don't have the TC seated as well as I think. Do you know what you get out of it if it's open circuited?

have two modules - one I use with a BS2P, that I know is working fine. Same result - must be doing something silly...

Post Edited (rePete) : 4/16/2007 2:42:51 AM GMT

rePete

do I need to call ow.reset in between each series of writeByte(XX) calls?

Mike Green

I believe you do have to call ow.reset before each command sequence so there would need to be one before the second ow.writeByte($CC).

lyons5959

Mike is right. You only need to call a reset for every set of commands.

Example

ow.reset 'get thermocouple voltage
ow.writebyte(SkipNet)
ow.writebyte(RdReg)
ow.writebyte($0E)
tCuV.byte := ow.readbyte

ow.reset 'get thermocouple voltage
ow.writebyte(SkipNet)
ow.writebyte(RdReg)
ow.writebyte($0F)
tCuV.byte[noparse][[/noparse]0] := ow.readbyte

T Chap

Here is some 2760 SX code Bean put together and I might have only slightly altered, maybe you can get some info from it, it works great btw. This code should read the temp and output a string with the temp once per sec.

rePete

Thanks all - got it working

ow.reset
ow.writeByte($CC)
ow.writeByte($69)
ow.writeByte($0E)

tc_volt.byte[noparse][[/noparse] 1]:=ow.readByte
tc_volt.byte[noparse][[/noparse] 0]:=ow.readByte

needed the extra reset - in my hasted I had accidentally multiplied by 15.625 twice - thought I was running a fever of 111 F [noparse]:)[/noparse]

rePete

for what it's worth

I think there are other (better) examples of using the DS2760 in the forums - but wanted to put up the start of a program that uses that module in case it is helpful. Also dropped in a small code to generate the thermocouple table.

Note my tc table is a bit odd - (farenheit-32)/15.625*1000 - looking up temperature by DS2760 units instead of microvolts

used the NIST coefficients for a ktype TC

Post Edited (rePete) : 4/16/2008 3:26:44 AM GMT

rePete

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