A/D counts vs voltage conversion

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Re: A/D counts vs voltage conversion

Post by Pontisteve » Sun May 18, 2014 1:43 am

I forgot about this thread, but just wanted to mention that at this point, it seems most likely that 5.115 is the reference voltage. I base this on the fact that I have seen over 5v a few times on VREF, and that all the numbers in tables add up and display nicely if you assume 5.115. It also puts A/D counts per volt at exactly 200.

For example, in the error code thresholds for min and max voltages, you often see 985 and 990 max, and 30 or 40 min. Dividing these by 200 works out voltages of 4.925, 4.95, .15, and .20 respectively. I also saw TPS min and max readings of 150 and 250, which works out to .75 and 1.25 volts. All these just seem to fit well. Using 5.00 or even 5.12 don't round so nicely.

So I'm a believer at 5.115 until someone convinces me otherwise.
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Re: A/D counts vs voltage conversion

Post by XantheFIN » Sun May 18, 2014 6:13 am

I won't bring anything useful but i see that year 94 EEC-IV which i have is using 5.12 (on FN044 and MAF) and from year 98 is 5.00 because MAF Voltages looks crap on 94 than 98. Other things is that 98 has weird engine size. Maybe someone wanted quick solutions.

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Re: A/D counts vs voltage conversion

Post by jsa » Sun May 18, 2014 4:30 pm

Could the input ADC's be ratiometric to Vref ?

If yes, then a/d count voltage value becomes a moot point, so long as sensor output is ratiometric.

MAF output could not be ratiometric to Vref, as they have a seperate 12v feed.

TPS is, as it is just a pot.
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Re: A/D counts vs voltage conversion

Post by Pontisteve » Sun May 18, 2014 5:02 pm

That's a good point I keep forgetting. Everything is VREF except the MAF. Since it gets a 12v input, it must be internally regulated. So how can I determine what its regulated to? I wouldn't even know if its a pull up or pull down design without depinning a wire or something.

Since it uses the same AD converter, wouldn't they want it referencing the same voltage as the other 5v sensors are regulated to?

I can't even short vref to signal without FMEM kicking in and substituting a value. Perhaps the only solution is to just simulate some 4.5 volts with a resistor to signal and measuring voltage and loggi g AD counts.
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Re: A/D counts vs voltage conversion

Post by tvrfan » Sun May 18, 2014 9:48 pm

I have been reading/scanning this thread, and it occurred to me that the questions about 1023 counts = 5.0V or 5.12v are actually completely irrelevant.

Why ?

Well remember that the raw A/D count is ALWAYS fed into one or more lookup functions to convert that value into something more meaningful for the EEC code, so any error can be corrected in those function numbers. An easy example is engine temp, where the Raw A/D is converted into a temperature value, which ALSO might be scaled in a useful manner for later calculations. On early Euro boxes this appears to be degrees C. I think the A9L is in degrees F ?

Remember that temp sensors are typically non-linear too, so the lookup functions take acount of this as well.

So there is plenty of places where any inherent 'error' can be eliminated.....at least down to typical build variations (a few percent or less)

[sorry if that's been said somewhere above - I didn't see it, so added it here....]
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Re: A/D counts vs voltage conversion

Post by Pontisteve » Mon May 19, 2014 2:30 am

The question is very relevant, particularly with the MAF. If you are trying to enter in a MAF flow sheet into various brands of software, you will find that the actual numbers you enter vary depending on the brand of software, and whether they believe the VREF for that sensor is 5.0 or 5.12 or whatever.

If you were dyno tuning the MAF, then what the software says MAF output is, is irrelevant as long as your commanded air/fuel = your target air/fuel. But if you manually enter in flow data, you have to get this right.

Also it would be handy to know what the correlation is if you were diagnosing a problem. You can read voltage under the hood, but would see AD counts in the scantool or SCT datalogs. Knowing for sure what the conversion factor is should be beneficial.
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Re: A/D counts vs voltage conversion

Post by jsa » Mon May 19, 2014 2:38 am

Pontisteve wrote:That's a good point I keep forgetting. Everything is VREF except the MAF. Since it gets a 12v input, it must be internally regulated. So how can I determine what its regulated to? I wouldn't even know if its a pull up or pull down design without depinning a wire or something.
The OEM Hitachi MAF on my thing supposedly will output greater than 5v. Apparently they'll go all the way to battery volts. Can't imagine the ADC being able to read that, or what voltage the ADC lets the smoke out.
Since it uses the same AD converter, wouldn't they want it referencing the same voltage as the other 5v sensors are regulated to?
That's not the case on my hardware. There are a pair of wires from the MAF to a pair of pins on the EEC-IV (9&50). Those pins run to a standalone device on the PCB and are at least 30kohm to Vref and Ground. The PCB label for it is RN3. The device is 6 pins. Pins 1 & 6 are from the MAF. I have not traced the other 4 entirely. The printing on the device is F07F-AA, DACO & 9436.
I can't even short vref to signal without FMEM kicking in and substituting a value. Perhaps the only solution is to just simulate some 4.5 volts with a resistor to signal and measuring voltage and loggi g AD counts.
Vref and the ground pins do not connect to any RN3 pins directly. I think you will need to try and external source.
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Re: A/D counts vs voltage conversion

Post by tvrfan » Mon May 19, 2014 1:09 pm

Pontisteve wrote:The question is very relevant, particularly with the MAF. If you are trying to enter in a MAF flow sheet into various brands of software, you will find that the actual numbers you enter vary depending on the brand of software, and whether they believe the VREF for that sensor is 5.0 or 5.12 or whatever.

If you were dyno tuning the MAF, then what the software says MAF output is, is irrelevant as long as your commanded air/fuel = your target air/fuel. But if you manually enter in flow data, you have to get this right.

Also it would be handy to know what the correlation is if you were diagnosing a problem. You can read voltage under the hood, but would see AD counts in the scantool or SCT datalogs. Knowing for sure what the conversion factor is should be beneficial.
Ah...right. I see your point. Sorry, I was thinking only in EEC code itself.
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Re: A/D counts vs voltage conversion

Post by Pontisteve » Mon May 19, 2014 1:33 pm

jsa wrote:The OEM Hitachi MAF on my thing supposedly will output greater than 5v. Apparently they'll go all the way to battery volts. Can't imagine the ADC being able to read that, or what voltage the ADC lets the smoke out.
I do believe the MAFs will output greater than 5 volts, perhaps all the way to battery voltage. (The slot MAFs apparently won't do that). But the PCM won't recognize more than 5.00 anyway.
jsa wrote:That's not the case on my hardware. There are a pair of wires from the MAF to a pair of pins on the EEC-IV (9&50). Those pins run to a standalone device on the PCB and are at least 30kohm to Vref and Ground. The PCB label for it is RN3. The device is 6 pins. Pins 1 & 6 are from the MAF. I have not traced the other 4 entirely. The printing on the device is F07F-AA, DACO & 9436.
Are you saying the MAF has it's own AD converter chip that isn't shared by other devices? Or just it's own input on the PCB?
jsa wrote:Vref and the ground pins do not connect to any RN3 pins directly. I think you will need to try and external source.
Not sure what you're trying to tell me here.
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Re: A/D counts vs voltage conversion

Post by jsa » Mon May 19, 2014 4:05 pm

Are you saying the MAF has it's own AD converter chip that isn't shared by other devices? Or just it's own input on the PCB?
Yes the maf has its own input to the pcb, that is cofigured different to other inputs.

RN3, might be "resistor network". Its other 4 pins need tracing, and/or testing, to find what it does, and connects too.
It's possible there is a different adc for the maf, tracing/testing is needed to determine that.
jsa wrote:Vref and the ground pins do not connect to any RN3 pins directly. I think you will need to try and external source.
Not sure what you're trying to tell me here.
You mentioned above, Vref to the input put the eec into fmem. Doing that to the maf input is unlikely to be successful because the maf input appears to be seperate from Vref and internal grounds up to RN3 at least.

I'm saying, use an external 5v source if you want to measure volts per a/d count.
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Re: A/D counts vs voltage conversion

Post by Pontisteve » Tue Jul 15, 2014 1:37 pm

Update. I had a breakout box hooked up to an 01 Cobra the other day, and decided to spend some time measuring this stuff.

Here is the raw data I took:

VREF at sensor relative to battery ground 5.05v
VREF at breakout box relative to battery ground 5.05v
VREF at breakout box relative to sensor ground 5.01v
VREF at sensor relative to sensor ground 5.01v
Battery negative to sensor ground 38mv

Now, checking the TPS sensor signal readings:

Idle volts at sensor relative to sensor ground .974
and according to scantool 1.00v
WOT volts at sensor relative to sensor ground 4.67
and according to scantool 4.77v
Part Throttle breakpoint at sensor to sensor ground 1.011 - 1.014v
and at scantool 1.04v
WOT breakpoint at sensor relative to sensor ground 3.91v
and at scantool 3.99v
VREF to Signal return at breakout box 5.02v (note: VREF voltage dropped some here, possibly due to battery voltage)
VREF at breakout box to sensor ground 5.02v

FYI, in this tune the PT breakpoint is 6 counts, and the WOT breakpoint is 560 counts. (More on that 560 later!)

Now, hooking up a datalogger and looking at AD counts live data versus voltage measured between TP Signal and Signal Return (both measured at breakout box):

Throttle Mode ABS TP Counts Voltage
CT 200 .981v
PT 207 1.015v
WOT 800 3.916v
Back to PT 760 3.733v

CT 201 .982v
Holding 1v 204.0 to 204.75 1.000v

Now, shorting VREF to TP signal by unplugging the TPS and using a paperclip:

5.01v @ breakout box
1023 AD counts (with some bobbling around between 1021 and 1023
5.05v @ sensor relative to battery negative

So what have we learned here? On this car, shorting VREF to signal produced 5.12v at the scantool. (Note: the scantool COULD be rounding up 5.115 to 5.12, I don't know). I do know that the voltage at the sensor (relative to sensor ground), and the voltage at the breakout box between TPS signal and signal return are about the same. So there is not a voltage drop in the wiring here, and it is not a ground issue. I also know that there is definitely more than 5 volts being sent out by the PCM. Apparently, there is 5.12v being sent out by the PCM over the VREF circuit. However, with all the sensors in the car plugged in, that voltage seems to be pulled down to somewhere closer to 5 volts. 5.05v in this case.

Measuring ground voltage drop, I see that 5.05v between VREF at the sensor and battery negative turns into 5.01v at the breakout box between VREF and Signal Return. The difference is that ground voltage of 38mv (.038v). Add that to the 5.01, and you've got your 5.05v.

What I can't quite account for is the difference in actual voltage going into the signal wire to the PCM, and the voltage that the scantool produces. When I measured 4.67 volts between sensor signal at WOT and sensor ground, the scantool says that I have 4.77 volts. I'm pretty sure this is because of data interpretation. The scantool doesn't actually see voltage. The voltage coming from the sensor signal is fed into the AD Converter input in the PCM, converted to an AD Count, and then the scantool is converting that AD count back into a voltage. So my 4.67v (multiplied by 204.6) becomes 955 AD counts. The scantool uses an AD conversion of 200 instead, and divides 955 by 200 to get 4.77 volts. Why 200? 1023 AD counts divided by 5.12 = 199.8. Or 1023 / 5.115 = 200. Not sure.

SCT says to use 204.6 as a conversion. And now I believe them. If VREF to Signal Return at the breakout box is 5.01v, and I jump VREF to TPS signal, I should be sending 5.01v to the AD Converter. The converter is reading 1023 at this point (albeit with some minor bobble due to the logging software probably). 1023/5 = 204.6.

Also, when I put my voltmeter between TPS signal and Signal Return at the Breakout Box, and then held the throttle dead steady with my foot until the voltmeter read 1.000v, the AD counts were 204.0 to 204.75, bobbling around slightly, and averaging 204.35 on the logger. Close enough to 204.6 for me.

When I held the throttle wide open at 4.67 volts (both at the sensor and at the breakout box) between TPS signal and Signal Return, I showed ~953.8 AD counts. That works out to 204.24 AD counts. Again, an imperfection probably related to the logging software more than anything. And again, close enough to 204.6 for me.

I believe that 5.12 VREF at the PCM becomes something closer to 5 or just over 5 at the sensor input, and that the sensors are probably designed to work within the 0 to 5 volt structure. Yet the PCM sees converts that 5v signal into AD Counts, and the calibration works in AD counts, not volts, so it just sees 0 to 1023 while the sensor sees 0 to 5. And the scantool thinks in terms of 5.12v = 1023, so it upconverts the AD count signal to a 5.12v range. And that's why I get more voltage on the scantool than I do on the sensor.

For calibration purposes, it's safe to say that 1v at the sensor or going into the PCM is seen as 204.6 AD counts. Which I found rather odd, considering so many things in the calibration coincide nicely with the 1023 = 5.115v or 5.12v theory. Perhaps the calibration engineers also had the same thinking, since the Voltage Regulator really is 5.12 volts. Seeing as how the sensor's output is affected by it's voltage input, I don't think it really matters.

The only thing I wish I had done is to unplug every sensor and see what VREF was at the breakout box.
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Re: A/D counts vs voltage conversion

Post by jsa » Tue Jul 15, 2014 8:21 pm

Cheers

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Re: A/D counts vs voltage conversion

Post by Pontisteve » Wed Jul 16, 2014 3:23 pm

According to that writeup, 1 LSB = 5mv. So 1,000 LSB = 5 volts. Which is the same as saying 5.115v = 1023 LSB. That could be looked at as 0 to 1023 is 5.115v, or 1 to 1024 is 5.12v.

What I know to be true is that holding the TPS signal at 1.000v showed ~ 204.6 AD counts. So 5v would = 1023 AD counts. I think the only mystery is how 5.12v on the VREF bus turns into 5v at the sensor. And I'm ready to believe that's just how much the sensors pull down the circuit. Guess I'll have to disconnect all sensors next time, and watch the VREF bus.

Not sure what LSB stands for... Linear Successive _____ perhaps?
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Re: A/D counts vs voltage conversion

Post by tvrfan » Wed Jul 16, 2014 3:59 pm

As an [ex] computer geek, generally LSB = least significant byte and MSB = most significant byte, or in other words lower and upper byte, in most cases.
(some CPU cores swop the byte orders around all over the place, which is why 'upper' and 'lower' aren't quite right).

The A/D uses 'successive approximation' technique, not sure what the acronym for that is.
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Re: A/D counts vs voltage conversion

Post by jsa » Wed Jul 16, 2014 5:37 pm

It's not hard to lose 0.12V with meters of wire and multiple crimped connectors. 5.12v also assumes absolute precision in the regulator. The bit value from the ADC also assumes absolute precision of the conversion. Reality is, the internal EEC electronics have tolerances as do the sensors and the equipment that calibrates the sensors and so on.

As tvrfan highlighted 'successive approximation', is literally an approximate value.

Here's a good document on ADC's
http://www.freescale.com/files/microcon ... AN2438.pdf

Ford made the EEC self learning to trim all these small variables among other things. Its a pretty fair bet that some EEC applications have transfer functions tweaked to suit the external electrical conditions particular to a vehicle model.
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Re: A/D counts vs voltage conversion

Post by decipha » Fri Jul 18, 2014 5:15 pm

The man already summed this up over a year and a half ago.

as for the FMM, just go max out the scalar and you can pull the value or log the ixxx to log the actual input
sailorbob wrote:The A-D converter is a 10 bit successive approximation register that provides 5 mV steps with a Vref of 5.12 volts. This is the manufacturer specification for the device.

You can only really write the equations in the definition according to the specifications of the device. Getting into the realms of saying that Vref differs and therefore you should not use 5.12 V is futile because all the input and outputs devices in the engine management system have tolerances and you simply cannot factor in all the possibilities.

If you want justification for use of 5.12 V in the A-D count to volts conversion you only have to look at how the values work out using this value in stock calibrations. Ford often use a value that has limited number of decimal places (typically 1 to 3)and using value other than 5.12 V results in tens of decimal places.

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Re: A/D counts vs voltage conversion

Post by BillMarkViii » Fri Aug 08, 2014 1:38 pm

Documentation of the actual hardware used on the EEC IV and V
Attachments
EEC-IV-hr_44-m.png
Binary math as used by Ford in the EEC
EEC-IV-hr_44-m.png (792.9 KiB) Viewed 11364 times
EEC-IV-hr_08-m.png
8065 add on AD
EEC-IV-hr_08-m.png (1.02 MiB) Viewed 11364 times
EEC-IV-hr_04-m.png
On chip AD
EEC-IV-hr_04-m.png (971.11 KiB) Viewed 11364 times
EEC-IV-hr_05-m.png
On chip AD related int records
EEC-IV-hr_05-m.png (1013.93 KiB) Viewed 11364 times

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Re: A/D counts vs voltage conversion

Post by Pontisteve » Mon Oct 03, 2016 3:55 am

Gentlemen, I need your thoughts once again on this subject.

While I've come to believe that Reference Voltage (VREF) is 5.12 volts, I would like to know exactly what voltage regulator came in EEC-IV and EEC-V processors. I want to dig deep on the manufacturers specs on that one, just to see. But I believe Derek is right, everything lines up awfully well when using 5.12v, and I have seen more than 5.00 volts on just about every VREF I tested with a Fluke meter. But these hardly even matter, except what's displayed in the software, because the A/D converter is taking 0 to VREF and turning it into 0 to 1023 AD Counts. So exactly what VREF is, is purely educational.

However, it's the MAF that's always been my focal point for this discussion. And tonight, I realized something. The PCM isn't supplying the MAF with VREF. The MAF is creating it's own signal, and even providing the PCM with it's own signal return. So this channel is unique, in that it doesn't rely on internal voltage regulators anyway. The MAF is designed to put out 0 to 5 volts, from everything I can see. And while there is a 16v limit at the top of many MAF transfer functions, there is a 5.00 volt limit on the rest. And even in 16v applications, all the software seems to have 5.000v as a top usable line.

The computer still inputs this signal into it's AD Converter, but perhaps this channel has an actual limit of exactly 5.00 volts = 1023 counts. Although I suspect that the AD converter's input voltage is the reference, and since there's only one ADC, all sensors must likely be referenced to it equally. But then why is the MAF limited to 5v in every tuning software, where the other sensors are supposedly referenced to 5.12v?
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Re: A/D counts vs voltage conversion

Post by jsa » Mon Oct 03, 2016 7:11 am

Follow the circuit from the maf input pins on the eec through to the analog legs on the actual 8061 or 8065 chip.

You will find the volts from the maf are processed and referenced to the eec 5v sensor reference within the eec..
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Re: A/D counts vs voltage conversion

Post by Pontisteve » Mon Oct 03, 2016 3:13 pm

I'm not sure I completely understand you. Since the MAF has it's own 12v power source and an output that can actually exceed 5 or 6 volts, the only other wires are Signal Return and Signal. The MAF provides it's own signal return (sensor ground), and then shares it to the PCM. I'm not sure exactly how it shares it, but I know the sensor provides the ground TO the PCM. The MAF signal goes into the same AD converter as everything else though, and my understanding is that the AD converter gets it's power from VREF 5.12v. All other sensors share the PCM's signal return, except the MAF.

Could you explain to me what you mean?
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Re: A/D counts vs voltage conversion

Post by jsa » Mon Oct 03, 2016 4:19 pm

You need to trace the circuit within the eec.

Your assumption the maf connects to the adc like all other analog inputs is incorrect.
[edit] It still connects to the ADC, but by different electronics compared to other inputs[/edit]

The electronics in the eec for the maf input tie the maf signal to the eec 5V.
Last edited by jsa on Mon Oct 03, 2016 8:05 pm, edited 1 time in total.
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Re: A/D counts vs voltage conversion

Post by Pontisteve » Mon Oct 03, 2016 4:35 pm

So the MAF signal doesn't go to the ad converter? And what do you mean it ties into the eec 5v? I don't understand what you're trying to tell me.
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Re: A/D counts vs voltage conversion

Post by jsa » Mon Oct 03, 2016 5:14 pm

The maf signal goes to the adc via other electronics in the eec that reference the maf 0-5V signal to the eec 5V.

I don't know how else to explain it to you.
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Re: A/D counts vs voltage conversion

Post by decipha » Mon Oct 03, 2016 6:38 pm

heres an aside

sometime in 96/98 when henry went from 2 bank to 4 bank ecus but not clear cut, the voltage conversion changed

most (prob all) 4 bank eec-v's have an equation of /13094.5 as opposed to /12800 in the older boxes

65535/12800=5.12
65535/13094.5=5.005

this is evident by the voltage values the engineers tossed in

yea yea true value is a/d but the math correlates to support it

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Re: A/D counts vs voltage conversion

Post by Pontisteve » Mon Oct 03, 2016 8:01 pm

jsa, why would the MAF go to other electronics, and not just go into the ADC like everything else? What's the point? There must be a point. And what other electronics are there, that would accept a MAF signal (and a unique MAF signal return)? There is signal conditioning to the MAF, but that's done in the software via the MAF filtered air mass logic.

Mike, that's interesting abut the 96/98. So maybe it's safe to say that 5.12v was the reference voltage in EEC-4 and 5.005 for EEC5 then? When you say they have an equation of 13094.5, what equation are you referring to? There's lots of equations.

And should we be punching in MAF voltages up to 5.12 in the EEC4 MAF transfer function, and not 5v? Even BE lists top lines as 5.000v.
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Re: A/D counts vs voltage conversion

Post by jsa » Mon Oct 03, 2016 8:07 pm

decipha wrote:heres an aside

sometime in 96/98 when henry went from 2 bank to 4 bank ecus but not clear cut, the voltage conversion changed

most (prob all) 4 bank eec-v's have an equation of /13094.5 as opposed to /12800 in the older boxes

65535/12800=5.12
65535/13094.5=5.005

this is evident by the voltage values the engineers tossed in

yea yea true value is a/d but the math correlates to support it
Interesting, any evidence of the 5V regulator hardware changing ?
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Re: A/D counts vs voltage conversion

Post by Pontisteve » Mon Oct 03, 2016 11:47 pm

I would very much like to know exactly what 5v regulators came in both EEC4 and 5.
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