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

Stan

 

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

 

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...
But, we pay for our wonderful winters with 100F+ May thru Sept!

 

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?

 

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.

 

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

 

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

 

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

 

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

 

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...