Thermometer Converts from Celsius?
 

The temperature around here has been fluctuating around 32 degrees last couple of days and I was noticing that the outside temperature read-out jumps from 32 to 34 or from 32 to 30. At first I thought that it was only showing even number degrees.

At colder temperatures I noticed it indicates in odd numbers. This makes me come to a conclusion that the temperature must be sent to the computer in Celsius and then converted to Fahrenheit.

I have a Japanese built Camry. Wondering if the US built are the same way. Not that it affects my life in the least little bit, but just curious of this little observation. I don’t recall my 2004 Camry having the same temperature behavior.

Re: Thermometer Converts from Celsius?
 

I haven't payed attention to this. I typically have my MFD set at the MPG screen so that's why I haven't noticed. I'll have to switch it over to the temp screen to check it out. I also have a Japan built TCH.

Re: Thermometer Converts from Celsius?
 

skata — All the internal car data is measured and transmitted in metric units (liters, kilometers, etc.). That's probably been true of all the car companies for decades now. That's one reason why the bolts have been metric for some time now. The CAN bus carries this metric data, which is being converted to US units for the US market. The Canadian TCHs are metric, and so read temperatures in degrees Celsius. You're probably right that the jumps seen in your degrees Fahrenheit readout is due to the conversion from Celsius to Fahrenheit — nearly two (actually 9/5) degrees F to each degree C.

Stan

Re: Thermometer Converts from Celsius?
 

Not that I want to highjack this thread, but has anyone noticed that the MFD thermometer readout seems to be always 2-4 degrees Fahrenheit higher than what's reported on the news? Looks like it may not be calibrated correctly, akin to the MPG and MPH readouts this forum has discussed in the past (i.e. MPG being off by 1-2% from manual calcs, MPH stating lower speeds than actual, etc).

This could be due to the thermometer being too close to the ICE (and measuring residual heat), but I've noticed this discrepancy even when the engine is "cold"...

FYI, for comparison purposes: my TCH is Japan-built, low(ish) VIN, US market (i.e. miles/Fahrenheit).

Re: Thermometer Converts from Celsius?
 

Mine seems to be pretty good. I have 2 wireless thermometers in different parts of my yard and all three seem to be pretty close to one another.

Re: Thermometer Converts from Celsius?
 

I agree - my thermometer has seemed very accurate compared to the remote outdoor thermometer at my house.

Re: Thermometer Converts from Celsius?
 

I agree, I find the temp readout to be very accurate to local conditions. My Sienna has a temp display too that is also pretty accurate. On both vehicles I've always been impressed how well it seems to handle sitting in the sun. Although it will register a few degrees high at startup, it seems to find the right temp pretty quickly after 3 or 4 of driving.

Re: Thermometer Converts from Celsius?
 

Today, in the desert SW, it is a balmy 60ish degrees F. The TCH's thermometer changed several times from 59-61, and back to 59 over a 30-45 minute errand run around town, never displaying 60.

(Just more info for this thread.)

Re: Thermometer Converts from Celsius?
 

This is what I was indicating in the begining of this thread. I don't recall my 2004 Camry skipping digits.

Re: Thermometer Converts from Celsius?
 

More info: Over the last few days the temps here have varied from mid 40s F to just over 70. I have noted the temps that our TCH displays in that range and their C conversion on the left, and on the right, as if the thermometer was in fact reading in C, and converting to F for display purposes:

Converting from F to C:........................ Converting from C to F
F ....... C............................................... C............F ... rounded/will display as
43........6.11 ............................................6......42.8......43
45........7.22 ............................................7......45.........45
46........7.77 ............................................8......46.4......46
48........8.88 ............................................9......48.2......48
50........10 ..............................................10......50........50
52........11.11 .........................................11......51.8.....52
54........12.22 .........................................12.......53.6....54
55........12.77..........................................13......55.4.....55
57........13.88..........................................14......57.2.....57
59........15 ............................................. 15......59........59
61........16.11 ..........................................16....60.8.......61
63........17.22 ..........................................17....62.6........63
64........17.77.......................................... 18.....64.4.......64
66........18.88 ..........................................19......66.2......66
68........20 ..............................................20......68.........68
70........21.11 ..........................................21....69.8.......70

So..It in fact appears that skata is right, the info is collected in degrees C and converted to F and then rounded to the nearest whole digit!

Re: Thermometer Converts from Celsius?
 

jbollt — One couldn't ask for better data than that!

Stan

Re: Thermometer Converts from Celsius?
 

There seems to be a potential fly in the ointment here! Look at the attached pages from the TCH Repair Manual's section on the air conditioning system. From the "Measurement Item/Range" and "Normal Condition" columns one can deduce quite a lot about the step size/resolution and number of binary bits being used by the data system in representing each of the variables in the list. From my reading of these pages, the Ambient Temperature Sensor (the second item in the list) is sending data with an increment (step) size of 0.25 degrees C, from a lower limit of -23.3 degrees C to an upper limit of +65.95 degrees C. This requires 358 levels, and so a 9-bit code would be needed (which can accommodate up to 2^9 = 512 levels).

If this is correct, the temperature data (in degrees C) steps in increments of 0.25 degrees C, which is steps of 0.45 degrees F, from -9.94 degrees F to +150.71 degrees F. The steps are apparently not 1 degree C!

jbollt, I'll leave it to you to see whether this can still explain the observed temperatures in degrees F.

Stan

Re: Thermometer Converts from Celsius?
 

Stan, I'm not a mathematician or engineer...however, I've looked at the attached doc you provided several times, and I see what you are referencing... the fact that it shows the AMBI TEMP SENS with a min. temp of -23.3 C, and max temp of 65.95C. The part about "358 levels, and 9-bit code" is, unfortunately, WAY above my head.

I do understand your paragraph:

"If this is correct, the temperature data (in degrees C) steps in increments of 0.25 degrees C, which is steps of 0.45 degrees F, from -9.94 degrees F to +150.71 degrees F. The steps are apparently not 1 degree C!"

You have a metric TCH, right? Do your outside temp readings in the TCH correlate with the steps you reference? Or are they rounded off?

edit: looked at the doc again, and it seems that it is talking about connecting an "intelligent tester." Could this be the where the 0.25 degrees C steps you mentioned are, rather than the actual sensor in the TCH?

Jeff

PS Somewhat related to the discussion...
we are experiencing 78 degrees F here in Tucson today... :angel:
But, we pay for our wonderful winters with 100F+ May thru Sept! :omg:

Re: Thermometer Converts from Celsius?
 

SPL is referring to the fact that provided temperature range from -23.3C to 65.95 for 89.25C difference, which could only be divided by .25C, if the divider was different, the temperature range would be different and if you divide 89.25 by .25 you get 357 steps plus one = 358. All digital computers use binary code, 0 and 1. So if you have 2 digits, you can describe 4 different numbers 00 =(0),01=(1),10=(2),11=(3) with 3 digits (or bits ) =8 numbers, 4 digits =16 etc, until you get to 8 digits called byte = 256 , which is not enough to send all 358 different possible readings, therefore Toyota should be using at least 9 digits, capable of total 512 numbers (0 to 511). It's just a computer way way of writing a number, nothing more . But the document talks about adjusted ambient temperature as well and it seems to me, that's where the numbers get rounded and possibly translated to F if required after the rounding is done, leaving your table still valid. I think it would be much easier to program C to F translation as the last step , in other words first they process raw binary data from sensor, adjust it, round it up and then display or add extra step to translate to F and then display in US cars. BTW, it seems the inside temperature data is there, but how do you display it?
or am I missing something obvious for all this years?

Re: Thermometer Converts from Celsius?
 

Peter, thanks for explaining the binary code to me! You must be a teacher, and a good one at that, because I actually understand that now...imagine, after all these years!

You also wrote: "BTW, it seems the inside temperature data is there, but how do you display it? or am I missing something obvious for all this years?"

At least on Auto-climate controlled cars, the HVAC system, of course, must read the inside temp, as one of many data points it uses to determine how to adjust the air flow, fan speed, amount of heat added, or AC compressor need etc. to keep the interior temp as requested by the user. Does it display this temp? Nowhere obvious. If so, it is hidden....like the actual vehicle speed (via GPS) is available on the NAV equipped TCHs in a hidden menu. Most GPS units also provide elevation data, but I have yet to find that (even in a hidden menu) on the TCHs Nav.

Re: Thermometer Converts from Celsius?
 

jbollt — Pete4 has answered most of your questions excellently, so I won't duplicate what he said. You ask about the metric temperature display; it's in whole degrees C only, and so is being rounded (or truncated) to full degrees. I would expect that this is being done in the display, and not before. I'm sure that the various ECUs that access this data on the CAN bus use the full precision data. I'd also expect that the display will do the necessary Celsius to Fahrenheit conversion for the US model — the US display is a different unit, since its gauges are labelled in mph and mpg. It may indeed be true that the Celsius temperature is being rounded to an integer before being converted to Fahrenheit, and if so it's bad software design in my opinion. This would account for the observed readings. I'd guess that, if only we knew the requisite codes, we could access the inside temperature (and many other useful things, like the motor-generator speeds, battery SoC, etc.) using ScanGauge's new XGauge feature. I don't know of any TCH-specific access codes yet published, and the Prius codes given on the ScanGauge Web site don't work. Help!

Stan

Re: Thermometer Converts from Celsius?
 

Dear Stan,

The solution is simple: the unit should be set to express the temperature in degrees Celsius. There is no need for the unit to convert; the user must think in metric terms.

david

Re: Thermometer Converts from Celsius?
 

Haha, I say "yay" but who knows what the rest of America would do.

Re: Thermometer Converts from Celsius?
 

Dear Mikie,

I arrived in the US from London in the Summer of 1960. When I went to school in upstate New York in September, 1960, I learned in the seventh grade Science class that the US was moving to metric through a process called gradualism. It is now 48 years later and I believe that I have been more than patient. Everything must now go metric immediately. The time for the burying of "gradualism" arrived long ago.

By the way, when I arrived here, the Yanks made fun of the Brit money system: 12 pennies to the shilling and 20 shillings to the pound. They told me that they had a far superior system of 100 cents to the dollar. The Brits changed the money system in the early Seventies and it is clear that the time for just revenge has arrived.

Metric now! Everyone will learn to think in metric when there is no choice.

Yours, david

Re: Thermometer Converts from Celsius?
 

Haha. Yes, I have heard that story of switching to the metric system before. Sadly it did not happen. No doubt because someone felt it would send the country into chaos! Ha.

It is funny how things evolve...

Re: Thermometer Converts from Celsius?
 

I remember in the 70s when Canada converted to metric. The gov't said, we're switching, that's all there is to it, get over it. The *****in' and moanin' and whinin' was pretty intense, but the world didn't come to an end. People learned and carried on with their lives. Same when the gov't converted from a $1 bill to a $1 coin because it was far more cost effective. Outrage, people refused to take it. But when the supply of $1 bills finally vanished and they had no choice, looking back, man what a waste of hot air. When the $2 bill gave way to the $2 coin a few yrs later, it was not nearly as big a deal. However, lately they have been toying with the idea of scrapping the expensive to make penny and rounding cash transactions to the nickel. Entire organizations have assembled to champion the cause of the penny. Oh the horror of paying $1.95 for coffee instead of $1.93. I digress but I guess the point is change is hard and people will always resist it no matter the possible benefit. Being much smaller population and used to more gov't control of things, I guess it was easier to drag Canadians kicking and screaming thru these changes than it could be done in the US.

Re: Thermometer Converts from Celsius?
 

Just some brief comments. In the metric TCH, the center console's temperature display increments in 0.5-degree Celsius steps. So, the internal temperature data certainly has at least this precision — likely much higher. I assume that in the US TCH the temperature increments in 1-degree Fahrenheit steps? [Incidentally, 0.5 degree Celsius is slightly finer than 1 degree Fahrenheit.]

Regarding the issue of metric units, I couldn't agree more with the comments expressed above.

Stan