Oil temp measuring

[JeepsAndGuns]

Ok, showing my noobness. I see this mentioned on this site a lot but have no idea what it means.
What is "A/D" Like you speak of just above.

[RobertISaar]

analog to digital:

it's how the PCM interprets sensors. long story shorter, the ECM reads a 0-5V sensor and then converts it into binary format so that it can know what a certain sensor is doing for all of it's various purposes.

[EagleMark]

Where's the 0 to 255 come in?

[RobertISaar]

well, the A/D system in these ECMs are 0-5 volt 8-bit converters. 0 volts means 0 A/D counts. 5 volts means 255 counts. each count is 0.01953125 volts. notice 255 * 0.01953125 = 4.98volts. can't express decimal 256 in 8 bit numbering.

if it was a 10-bit system(like the autoPROM has), then it would be 0 to 1023 counts. assuming a 5 volt system, each count is 0.0048875855327468230694037145650049 volts.

notice, it's 2 to the nth power minus 1. 2 being that there are only two states (binary 1 and 0), and N being the bit resolution. 2^8 = 256, then subtract 1 due to not being able to express $100(decimal 256) in 8 bit format, and you have the 0-255 range.



now, once you get that figured out, think about the other analog inputs that are used by the ECM that aren't 5 volts... O2 sensor is 0-roughly 1.127 volts over a 0-255 range. and then you have ignition and fuel pump voltage available in a 0-25.5 volt range.... to read over 5 volts with a 5 volt A/D converter, you need to make a voltage divider network. let's say we have a 0-10 volt sensor, since it's easy to calculate. we make a voltage divider with the sensor signal going through a resistor (let's say a 1K, since it's a common unit), then on the other side of this 1K resistor, there is another 1K resistor, this one connected to ground. now, the A/D channel will be connected between the two resistors(since before the first will still be 10 volts and after the second will be ground), and that will allow a 0-10V sensor to be read using a 0-5V A/D unit.

the O2 sensor.... well, that's why the O2 sensor amplifier is there. i'm not entirely certain how it works, but from what i understand, it simply takes the 0-1.127 volt signal and multiplies the voltage by a factor of ~4.43, and at that point, it outputs a signal for the A/D system to read.

[JeepsAndGuns]

Umm, so in laymans terms, its just a lot of un used possiable sensor inputs?

[RobertISaar]

depending on the mask you want to run, yes. certain ones only want to see the basic coolant temp, IAT, TPS, MAP and maybe a couple of others...

some want those + trans temp, oil temp, a/c pressure, etc, etc....



keep in mind, that was a description only for the analog inputs, there are also discrete inputs, which are a little less confusing to explain, those are basically switches.

[EagleMark]

Umm, so in laymans terms, its just a lot of un used possiable sensor inputs?

well, the A/D system in these ECMs are 0-5 volt 8-bit converters. 0 volts means 0 A/D counts. 5 volts means 255 counts. each count is 0.01953125 volts. notice 255 * 0.01953125 = 4.98volts. can't express decimal 256 in 8 bit numbering.

if it was a 10-bit system(like the autoPROM has), then it would be 0 to 1023 counts. assuming a 5 volt system, each count is 0.0048875855327468230694037145650049 volts.

notice, it's 2 to the nth power minus 1. 2 being that there are only two states (binary 1 and 0), and N being the bit resolution. 2^8 = 256, then subtract 1 due to not being able to express $100(decimal 256) in 8 bit format, and you have the 0-255 range.

I think he said 0 to 5.0 volts is divided by 256 counts, expressed as 0 to 255 because computers count from 0.

Haven't tried to figure out the other one yet...

[RobertISaar]

correct, Mark.