TMP04 temperature sensor ? ?

Don Pomplun · 2006-03-16 16:23

SEARCHing finds no hits for the AD TMP04 temperature sensor, so I'll ask if anyone has tried these with the Stamp. It outputs a TTL level pulse train at about 30 Hz whose duty cycle is linearly proportional to temperature. I'd like to incorporate temperature control as a lab project in my upcoming course, and this seems like a good candidate without having to add analog input circuitry.
TIA
Don

Tracy Allen · 2006-03-17 02:16

Try this from one of Prof. Peter Anderson's highly motivated students:
www.phanderson.com/stamp/tmp04.html

That shows how easy it is to read the high and low times with PULSIN. The math there can be greatly simplified.
The calculation of temperature uses this formula:
TC_CALC: ' 2350 - (4000 * T1)/T2
and in the program the multiplication is done in a highly instructive manner as 4000 iterated additions and the diviision also as iterated subtractions.

If you want to pursue it, I could hobble together something faster and shorter using the Stamp's ** operator and a quick binary long division.. Also instructive, in its own way.

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Tracy Allen
www.emesystems.com

Paul Sr. · 2006-03-17 13:28

Tracy Allen said...
Try this from one of Prof. Peter Anderson's highly motivated students:
www.phanderson.com/stamp/tmp04.html

That shows how easy it is to read the high and low times with PULSIN. The math there can be greatly simplified.
The calculation of temperature uses this formula:
TC_CALC: ' 2350 - (4000 * T1)/T2
and in the program the multiplication is done in a highly instructive manner as 4000 iterated additions and the diviision also as iterated subtractions.

If you want to pursue it, I could hobble together something faster and shorter using the Stamp's ** operator and a quick binary long division.. Also instructive, in its own way.

Dr. Allen,

I would definately like to see that if you have the time to put it together. I do have the components from Prof. Anderson..

TIA,
Paul

Don Pomplun · 2006-03-17 16:32

Good news -- looks like the TMP04 is a winner. There a few gotchas associated with the integer arithmetic & 16 bit word limitations. The device defines Farenheit temperature as 455 - (720 * Ton / Toff) . Numbers returned by pulsin are in the thousands, so you have to be careful of overflows. The code below outputs the temperature in 1/100ths of degrees, though no claim is made for that accuracy. Blasting the TO-92 device with a can of Freeze, or a hair dryer works well from temperatures down in the 20's, and up over 130. Still have to watch for numbers out of the 16 bit range, but it should work well for a temperature control lab. Somewhere on the Parallax site I saw an excellent writeup on PID, which I'll probably steal ;=)
These devices are over $5 at DigiKey, even though the Analog Devices site shows them as half that in quantity. This might be a candidate for the Parallax store, eh?
-- Don

Ton VAR Word
Toff VAR Word
Temp VAR Word

start: PULSIN 0,1,Ton
PULSIN 0,0,Toff
Toff=Toff/100
Temp = 10*Ton/Toff*72
Temp=45500-Temp
DEBUG "Ton=", DEC Ton," Toff/100=",DEC Toff, " 100xTemp=", DEC Temp, CR
PAUSE 1000
GOTO start

Tracy Allen · 2006-03-17 19:11

Hi Don,

That calculation makes it easy! I looks to me like that would give a real resolution of about 1/3 degree Fahrenheit.

The data sheet informs us that T1 (Ton) will be around 10 milliseconds, 12 maximum, and does not depend much on temperature, while T2 (Toff) will range from around 44 milliseconds at 125 degC down to around 15 milliseconds at -25 degC. On the Stamp, that is PULSIN values in the range of Toff = 7500 to 22000 (at 2 microseconds per count), and around 5000 for Ton.

Don, are those values typical of what you are seeing?

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Tracy Allen
www.emesystems.com

Don Pomplun · 2006-03-17 19:50

Hi Tracy,
I guess I hadn't read the (16 page) data sheet very carefully, especially the part about Ton being pretty constant. But, yes it does seem to follow that. It's a little tough to follow my quick temp changes, but Ton seems to hover around 8.3 - 8.4 ms over a temp range of 4 - 117 F (pulsin values of 4144 - 4226). Over that same range, the Toff variation is 13.4 - 18.1 ms (pulsin 6694 - 9055).
What I tried may not be the optoimal approach for getting the best temperature reading. It was just the first thing that worked! It will start out being a good class discussion on the topic of overflow, and overcoming the limitations of integer arithmetic.
It looks like it should give enough resolution to do a temperature control lab.
-- Don

Tracy Allen · 2006-03-17 23:18

Here is another version that gives better precision:

' {$STAMP BS2pe}
' {$PBASIC 2.5}
' TMP04.bse
' version author: Tracy Allen, EME Systems
' Code for TMP04 temperature sensor (Analog Devices)
'  Temperature proportional to duty cycle
' degrees Fahrenheit = 455 - (720 *T1/T2)
' where T1 and T2 are as in data sheet, time high and time low
' program displays various intermediate values, including:
' --- compute1: easy calculation
' --- compute2: using binary long division to comute T1/T2

t1 VAR Word
t2 VAR Word
degf VAR Word
idx VAR Nib

DO
  PULSIN 15,1,t1
  PULSIN 15,  0,t2
  DEBUG DEC t1,TAB,DEC t2,TAB
  GOSUB compute1
  DEBUG DEC degf/100,".",DEC2 degf,TAB
  GOSUB compute2
  DEBUG DEC degf/100,".",DEC2 degf,CR
  PAUSE 100
LOOP

compute1:
  degf = t2/100
  degf = 10*t1/degf*72
  degf  = 45500 - degf
  RETURN

compute2:
  FOR idx=15 TO 0   ' binary long division
    t1 = t1 // t2 << 1
    degf.BIT0(idx) = t1/t2
  NEXT
  DEBUG TAB,DEC degf,TAB   ' intermediate result T1/T2 = degF/65536
  degf = 22750 - (36000**degf) * 2   ' values * 5 * 2
  RETURN

I did have a TMP04 (out of a box of samples!) At room temperature, I was getting T1 = 4346 and T2 = 8177 from a BS2pe. Using the data sheet formula, the temperature is 455 - (720 * 4346/8177) = 72.326 degrees Fahrenheit.

The easy compute1 formula loses precision in the T2/100 step, which is necessary to keep the computation in bounds, and it comes up with a reading of 69.08 degrees Fahrenheit, with a resolution of about 4.3 degrees. Did I get your formula right Don? As the sensor warmed up, the reading went from 69.08 to 73.4

The compute2 routine first uses binary long division to compute T1/T2 , approximated by the fraction degf/65536, and it finishes the computation to give a reading of 72.34 degrees Fahrenheit, with a resolution of 0.02 degrees.

I don't know if your students would be scared by the binary long division, but they shouldn't be. It is one of the most useful routines for math work/sensor signal processing on the Stamp.

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Tracy Allen
www.emesystems.com

Tracy Allen · 2006-03-18 18:30

Hi Don,

I was taken aback by the course 4.3 degree resolution in the compute1 algorithm, but it makes sense when you follow it through. Here is an improvement, not quite as good as compute3, but about 0.3 degree Fahrenheit. (The accuracy Analog Devices claims for the sensor is 1.5 degrees Celsius typical, 4 degrees worst case).

compute3:  ' uses remainder from division to get an extra significant figure
  degf = t2 / 10
  degf = 10 * t1 / degf * 10 + (10 * t1 // degf * 10 / degf) 
  degf = 45500 - (degf * 72)
  RETURN

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Tracy Allen
www.emesystems.com

Don Pomplun · 2006-03-21 06:46

Tracy,
Thanks for the effort on your temperature Compute algorithms. It took some "soul searching" to the early days of long division to sort out. I like the 3rd one even better ;=)
Regards,
Don

TMP04 temperature sensor ? ?

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