Datalogging & Video Solutions for C5
06-20-2016, 09:31 AM
#2
Pro
Depends what data you want to log. There really is no plug and play solution to get data out of the obd2 port like there is on the C6. This weekend we wired Race Tech dash to my C5 and tapped into the stock sensors to get the data we wanted.
06-20-2016, 11:44 AM
#3
Drifting
see https://www.corvetteforum.com/forums...video-how.html
you can cobble together something using a camera, GPS, and a smartphone app. You could do all of that just using one smartphone or could combine a few devices. That thread has a bunch of info and links to a few other threads on the same topic.
you can cobble together something using a camera, GPS, and a smartphone app. You could do all of that just using one smartphone or could combine a few devices. That thread has a bunch of info and links to a few other threads on the same topic.
06-20-2016, 09:36 PM
#5
Drifting
how much do you want to spend, are you looking to get really in the weeds with the data, or just overlay some data onto video?
06-20-2016, 10:40 PM
#6
Pro
Look at the Harry's Laptimer. It's by far the best amateur buy at under $50. Add blue tooth OBD II, wifi GPS, and a phone mount for an extra $275 (links to all of these options are listed on their site). All in you are at $325 plus a smart phone (assuming you already have one). After that, you have the AIM Solo DL for several hundred that essentially does the same thing. And then systems into the thousands if you want more sensors and data logging.
Last edited by SunnydayDILYSI; 06-20-2016 at 10:41 PM.
06-21-2016, 02:13 AM
#8
Pro
Did that work? I've been doing some research on this as I want to get reliable data logging working. I've been told tapping into the existing stock sensors will affect the signals and make them partially inaccurate. Apparently the best thing to do is add additional dedicated sensors for the items you want to collect. Surprised there isn't a simpler solution.
Last edited by Grabbed_Crow_Mobe; 06-21-2016 at 02:15 AM.
06-21-2016, 12:13 PM
#9
Safety Car
Cliff notes:
C5 data bus sucks.
Tapping into the OEM sensors has no effect.
----------------------------------------
Here is some rudimentary info on logging on a C5 and, I think, an '05 C6 (i.e., pre-CAN implementation cars).
The OBD2 databus on the C5 is bandwidth limited. Typically, basic "real" race car logging is done at a rate of at least 100Hz (inputs are sampled at 100 times per second). You can obviously knock this down for certain sensors (e.g., water temp) that do not rapidly change, but you would want, at a bare minimum, 20Hz on things like oil pressure, throttle position, brake pressure, steering angle and fuel pressure, among other things. 100Hz is typically ideal for these as it will give a complete picture of what that sensor is seeing. For other things, like shock position, you want something in the range of 1Khz.
The C5 OBD2 bus has a variable rate, but can be quite slow. Additionally, the C5 OBD2 data stream mainly carries engine parameters and not things that are useful for driving (e.g., brake pressure, steering angle, lat/long g, yaw). The C5 is "sensored up" (especially the active suspension cars) but the data is not available on the bus.
So, the alternative is to get a logger that has a decent number of analog inputs or swap to an aftermarket ECU with a "modern" 1Mb CAN bus with configurable bus settings, and send that to a logger or log internally (assuming the ECU supports GPS/track mapping). Swapping ECUs is costly and time consuming and the modern GM PCMs are pretty capable, and in some cases have capabilities you will not find on an aftermarket ECU.
If you take the route of adding a logger with a variety of analog inputs (examples include the Race Technology DL-1, various AIM loggers, Motec, Pectel etc etc), you can tap into the OEM sensors. As a background there are three common types of sensors on a C5 - thermistors (oil and water temp), active resistance sensors (pedal and throttle plate position, and shock position on the F45 cars) and active sensors that output a voltage.
For the latter two, you can tap into those with absolutely zero effect on what the PCM sees. The main issue is whether there is enough current to provide output to both the PCM and the logger, and the loggers have an input impedance of at least 100k ohms, meaning they draw something in the range of a couple milliamps, which is for all intents and purposes, nothing (see below for further explanation).
For the thermistors, lets understand how the PCM reads a thermistor - the thermistor is simply a variable resistor that changes its resistance based on temperature. ECUs do not read resistance (directly) - instead they read voltage. To convert a thermistor's output to voltage, the PCM has an internal voltage divider (aka "pull-up resistor"). For the C5's water temp sensor circuit, this is approximately a 390 ohm resistor at temps above 120F (i.e., at the point when voltage in the water temp sensor circuit drops below 1v, once the voltage drops below 1v, the PCM performs a level shift and the effective pull-up changes to about 4100 ohms; the PCM/DIC appears to take a "regular" single-pull up approach to oil temps). Thus, the wire going from the thermistor (temp sensor) to the PCM's input now has a voltage (instead of a resistance) and the PCM is happy. Since it now shows a varying voltage, the non-ground wire going from the thermistor to the PCM behaves like the output from pedal position sensor and the throttle body (and the oil pressure sensor) and you can tap into that wire and connect it to the logger.
To understand what occurs when you tap into a wire carrying voltage, think about what happens when your car's A/C and radiator fans are on. The load on the alternator is high and the alternator needs to work hard to keep up. If you also had a huge stereo, the headlights could dim (depending on the music) because the alternator cannot keep up with the load (i.e., cannot provide enough current) and the headlights indicate a sage in voltage.
Now back to the temp sensor - the PCM is providing a 5 volt signal (through the pull up resistor) to the temp sensor circuit, loosely analogous to how an alternator provides power to the car. We have the same concern here - does the PCM's 5v power source have enough current to keep up with the additional load (without a resulting dip in voltage) caused by tapping into the temp sensor wire and hooking it up to a logger?
The answer is yes, and it isn't even close. For example, a DL-1 has an input impedance of about 100k ohms. For all intents and purposes, it presents a load of approximately nothing, in terms of current (you can do your own calcs using Ohm's law, but adding the DL-1 presents an essentially invisible additional .05 milliamp load, assuming the PCM also has a 100k input impedance). Because the logger draws approximately no current, the voltage will not be affected (and thinking back to the prior example, the headlights will not dim) and accuracy of the temp sensor reading (i.e., voltage) going to the PCM and the logger will be identical.
C5 data bus sucks.
Tapping into the OEM sensors has no effect.
----------------------------------------
Here is some rudimentary info on logging on a C5 and, I think, an '05 C6 (i.e., pre-CAN implementation cars).
The OBD2 databus on the C5 is bandwidth limited. Typically, basic "real" race car logging is done at a rate of at least 100Hz (inputs are sampled at 100 times per second). You can obviously knock this down for certain sensors (e.g., water temp) that do not rapidly change, but you would want, at a bare minimum, 20Hz on things like oil pressure, throttle position, brake pressure, steering angle and fuel pressure, among other things. 100Hz is typically ideal for these as it will give a complete picture of what that sensor is seeing. For other things, like shock position, you want something in the range of 1Khz.
The C5 OBD2 bus has a variable rate, but can be quite slow. Additionally, the C5 OBD2 data stream mainly carries engine parameters and not things that are useful for driving (e.g., brake pressure, steering angle, lat/long g, yaw). The C5 is "sensored up" (especially the active suspension cars) but the data is not available on the bus.
So, the alternative is to get a logger that has a decent number of analog inputs or swap to an aftermarket ECU with a "modern" 1Mb CAN bus with configurable bus settings, and send that to a logger or log internally (assuming the ECU supports GPS/track mapping). Swapping ECUs is costly and time consuming and the modern GM PCMs are pretty capable, and in some cases have capabilities you will not find on an aftermarket ECU.
If you take the route of adding a logger with a variety of analog inputs (examples include the Race Technology DL-1, various AIM loggers, Motec, Pectel etc etc), you can tap into the OEM sensors. As a background there are three common types of sensors on a C5 - thermistors (oil and water temp), active resistance sensors (pedal and throttle plate position, and shock position on the F45 cars) and active sensors that output a voltage.
For the latter two, you can tap into those with absolutely zero effect on what the PCM sees. The main issue is whether there is enough current to provide output to both the PCM and the logger, and the loggers have an input impedance of at least 100k ohms, meaning they draw something in the range of a couple milliamps, which is for all intents and purposes, nothing (see below for further explanation).
For the thermistors, lets understand how the PCM reads a thermistor - the thermistor is simply a variable resistor that changes its resistance based on temperature. ECUs do not read resistance (directly) - instead they read voltage. To convert a thermistor's output to voltage, the PCM has an internal voltage divider (aka "pull-up resistor"). For the C5's water temp sensor circuit, this is approximately a 390 ohm resistor at temps above 120F (i.e., at the point when voltage in the water temp sensor circuit drops below 1v, once the voltage drops below 1v, the PCM performs a level shift and the effective pull-up changes to about 4100 ohms; the PCM/DIC appears to take a "regular" single-pull up approach to oil temps). Thus, the wire going from the thermistor (temp sensor) to the PCM's input now has a voltage (instead of a resistance) and the PCM is happy. Since it now shows a varying voltage, the non-ground wire going from the thermistor to the PCM behaves like the output from pedal position sensor and the throttle body (and the oil pressure sensor) and you can tap into that wire and connect it to the logger.
To understand what occurs when you tap into a wire carrying voltage, think about what happens when your car's A/C and radiator fans are on. The load on the alternator is high and the alternator needs to work hard to keep up. If you also had a huge stereo, the headlights could dim (depending on the music) because the alternator cannot keep up with the load (i.e., cannot provide enough current) and the headlights indicate a sage in voltage.
Now back to the temp sensor - the PCM is providing a 5 volt signal (through the pull up resistor) to the temp sensor circuit, loosely analogous to how an alternator provides power to the car. We have the same concern here - does the PCM's 5v power source have enough current to keep up with the additional load (without a resulting dip in voltage) caused by tapping into the temp sensor wire and hooking it up to a logger?
The answer is yes, and it isn't even close. For example, a DL-1 has an input impedance of about 100k ohms. For all intents and purposes, it presents a load of approximately nothing, in terms of current (you can do your own calcs using Ohm's law, but adding the DL-1 presents an essentially invisible additional .05 milliamp load, assuming the PCM also has a 100k input impedance). Because the logger draws approximately no current, the voltage will not be affected (and thinking back to the prior example, the headlights will not dim) and accuracy of the temp sensor reading (i.e., voltage) going to the PCM and the logger will be identical.
Last edited by RX-Ben; 07-13-2016 at 12:36 PM. Reason: fixed PCM pull-up resistor value based on temp/volt readings
The following 5 users liked this post by RX-Ben:
FlashMsg (03-04-2020),
Grabbed_Crow_Mobe (06-23-2016),
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StreetSpeed (06-21-2016)
06-21-2016, 01:33 PM
#10
Pro
Did that work? I've been doing some research on this as I want to get reliable data logging working. I've been told tapping into the existing stock sensors will affect the signals and make them partially inaccurate. Apparently the best thing to do is add additional dedicated sensors for the items you want to collect. Surprised there isn't a simpler solution.
The following 2 users liked this post by StreetSpeed:
Grabbed_Crow_Mobe (06-23-2016),
MySR71 (06-23-2016)
06-23-2016, 12:12 AM
#11
Pro
06-23-2016, 12:13 PM
#12
Pro
I too want to say thanks for the info. I've spliced into a number of sensors on my C5 but didn't think I could do so on the water temp sensor as it isn't powered. However, it sounds like it is indeed possible and that I should give it a try.
Thanks again!
Thanks again!
06-23-2016, 12:29 PM
#13
Safety Car
Thank you, actually, I think. Didn't you post the equation years ago for decoding the steering wheel position sensors?
Due to "processing" inside the PCM, the DIC water temp will not line up to the temp at the logger (i.e., the logger will spit out the # that the thermistor/voltage divider math dictates, which was ~4deg F off ~125F). Oil temp sensor was on temporary leave, but I would think a similar PCM temp drift applies there too. If you absolutely need to have the temps the same, you can put together a voltage vs temp look-up table, which the R-T software now supports.
Due to "processing" inside the PCM, the DIC water temp will not line up to the temp at the logger (i.e., the logger will spit out the # that the thermistor/voltage divider math dictates, which was ~4deg F off ~125F). Oil temp sensor was on temporary leave, but I would think a similar PCM temp drift applies there too. If you absolutely need to have the temps the same, you can put together a voltage vs temp look-up table, which the R-T software now supports.
06-23-2016, 12:54 PM
#14
Pro
Yes, I do have some earlier posts about monitoring steering wheel position. I'm not sure I'm using the same scheme now that I did then. I log both output wires from the sensor. If I recall correctly, one is used for angle (up to 180 degrees of steering wheel position) and the other is used to determine if the angle is positive or negative. I can post it if you'd like.
For oil temp, I've spliced into the wire leading to the dash. I'm not sure if this signal is raw from the sensor or manipulated by one of the computers. I assumed it was manipulated. I idled the car for awhile and wrote down voltage vs. oil temp on the dash (DIC) to generate the calibration data.
For oil temp, I've spliced into the wire leading to the dash. I'm not sure if this signal is raw from the sensor or manipulated by one of the computers. I assumed it was manipulated. I idled the car for awhile and wrote down voltage vs. oil temp on the dash (DIC) to generate the calibration data.
06-23-2016, 06:18 PM
#16
Pro
Here's what I have been using.
Steering Angle:
Like I said before, I'm measuring both output signals from the steering wheel position sensor. I then process these with this formula:
IF('Steering Angl 1'>2.5, 36*'Steering Angl 2',-36*'Steering Angl 2')
Throttle Position:
Voltage Output (%)
0.5893 0
2.569 100
Brake Pressure:
I don't have a calibration curve for this as I have no info on the sensor. So I read and display the measured voltage.
Gear Indicator:
I use ratios of RPM/MPH to determine which gear is being used. My car has a base C5 transmission and I use this formula. It isn't perfect.
IF('RPM/MPH'>142.,0.0,IF('RPM/MPH'>126.,1.0,IF('RPM/MPH'>75.,2.0,IF('RPM/MPH'>48.,3.0,IF('RPM/MPH'>37.,4.0,IF(25,5.0,6.0))))))
Oil Pressure:
Voltage Output (psi)
1.8531 42
2.7255 67
Oil Temperature:
As mentioned previously, I've spliced into the oil temp wire going to the dash.
Voltage Output (degF)
1.1091 242
2.7095 144
I have some other sensors but their calibrations aren't really relevant. Someday I'd like to get wheel speeds.
Steering Angle:
Like I said before, I'm measuring both output signals from the steering wheel position sensor. I then process these with this formula:
IF('Steering Angl 1'>2.5, 36*'Steering Angl 2',-36*'Steering Angl 2')
Throttle Position:
Voltage Output (%)
0.5893 0
2.569 100
Brake Pressure:
I don't have a calibration curve for this as I have no info on the sensor. So I read and display the measured voltage.
Gear Indicator:
I use ratios of RPM/MPH to determine which gear is being used. My car has a base C5 transmission and I use this formula. It isn't perfect.
IF('RPM/MPH'>142.,0.0,IF('RPM/MPH'>126.,1.0,IF('RPM/MPH'>75.,2.0,IF('RPM/MPH'>48.,3.0,IF('RPM/MPH'>37.,4.0,IF(25,5.0,6.0))))))
Oil Pressure:
Voltage Output (psi)
1.8531 42
2.7255 67
Oil Temperature:
As mentioned previously, I've spliced into the oil temp wire going to the dash.
Voltage Output (degF)
1.1091 242
2.7095 144
I have some other sensors but their calibrations aren't really relevant. Someday I'd like to get wheel speeds.
06-24-2016, 10:31 AM
#18
Safety Car
Thanks for that.
From what I can tell/info that I found, the OEM brake psi sensor is a 2000 psi sensor, with a min of .2v and a max of 4.8v. Usually the ranges for these types of sensors are like .25 to 4.75 or the like, but the actual psi doesn't matter for analysis. Here is the equation I use: Y= (435 * x) - 87
Also, I tapped into the APP1 sensor (note sure if you went directly to the throttle body) - the voltages for APP1 are ~.6V (0%) and ~3.0V (100%).
I was planning to tap into the yaw sensor, which has a zero point of 2.5v. I don't have a translation for the sensor and instead was just going to use the voltage traces for comparison.
A while ago I was going to try to add-on the F45 shock position sensors but just ditched it for traditional linear pots as the OEM setup is pretty bulky. If you wanted to, you could tap into the individual wheel speed sensors (and create custom channels to show how the diff is working and rear tire slip), but you'll need to convert the signals to something the DL-1/a logger's digital inputs can use (Race Tech sells a converter). Could obviously log the trans temp if you have a Z06. I can't think of anything else, in terms of OEM sensors, that would be useful for driving analysis.
From what I can tell/info that I found, the OEM brake psi sensor is a 2000 psi sensor, with a min of .2v and a max of 4.8v. Usually the ranges for these types of sensors are like .25 to 4.75 or the like, but the actual psi doesn't matter for analysis. Here is the equation I use: Y= (435 * x) - 87
Also, I tapped into the APP1 sensor (note sure if you went directly to the throttle body) - the voltages for APP1 are ~.6V (0%) and ~3.0V (100%).
I was planning to tap into the yaw sensor, which has a zero point of 2.5v. I don't have a translation for the sensor and instead was just going to use the voltage traces for comparison.
A while ago I was going to try to add-on the F45 shock position sensors but just ditched it for traditional linear pots as the OEM setup is pretty bulky. If you wanted to, you could tap into the individual wheel speed sensors (and create custom channels to show how the diff is working and rear tire slip), but you'll need to convert the signals to something the DL-1/a logger's digital inputs can use (Race Tech sells a converter). Could obviously log the trans temp if you have a Z06. I can't think of anything else, in terms of OEM sensors, that would be useful for driving analysis.
Last edited by RX-Ben; 06-24-2016 at 11:08 AM.
06-24-2016, 08:01 PM
#19
Pro
Thanks for the brake pressure sensor info. Not sure if I'll use it or leave it be. The pressures don't mean much to me. If someone was apprehensive about connecting to the brake pressure sensor, they can splice into the brake pedal's brake light activation switch under the dash. It will only by an on/off reading but could be of interest. If a person wants to see if active handling is being activated, they can log both. You will see the brake pressure sensor values rising without the brake pedal being activated.
I too have spliced into the APP sensor. I set the ranges with the ignition on but car not running. Off throttle pedal for 0%, full throttle for 100%. Interesting that my calibration is so different.... Hopefully I am getting full throttle.
Funny about the shock position sensors. I have linear sensors on my car but my data system won't do everything I want with them and I looked into adding the F45 sensors instead. I didn't as they still wouldn't get me what I want I don't think. My data system, Racepak G2X Pro, doesn't have enough resolution in the analogue-to-digital converter. I want to differentiate the data and get low speed data (<1"/sec) but it won't do it as there isn't enough bits to get that fine of resolution. Plenty of sampling frequency, just not enough discretization. The F45 sensors looked attractive because of their shorter stroke but it still wouldn't be enough I don't think. I need higher resolution. Oh well.....
Thanks for the info on the Race Technology wheel speed sensor converter. I hadn't seen those and will look into them a bit.
I've thought about splicing into the Manifold Air Pressure sensor but I'm not sure what I'd do with the info. I'm not looking for max horsepower so intake development isn't really of interest to me. Intake air temp might be interesting.
I have been playing with IR tire temp sensors. That's my newer "toy." I've had rear sensors for while but just added fronts. I was logging accusump activation while I had one but have since dry-sumped. Thought about adding a pressure sensor to the oil pan to log vacuum. It would be more for engine health monitoring. Trans and diff temps are logged as is ambient temp. These temps are done with non-factory sensors that I've added.
As you can tell, most of this is for fun. There are some good books on data interpretation and it has been fun learning.
I too have spliced into the APP sensor. I set the ranges with the ignition on but car not running. Off throttle pedal for 0%, full throttle for 100%. Interesting that my calibration is so different.... Hopefully I am getting full throttle.
Funny about the shock position sensors. I have linear sensors on my car but my data system won't do everything I want with them and I looked into adding the F45 sensors instead. I didn't as they still wouldn't get me what I want I don't think. My data system, Racepak G2X Pro, doesn't have enough resolution in the analogue-to-digital converter. I want to differentiate the data and get low speed data (<1"/sec) but it won't do it as there isn't enough bits to get that fine of resolution. Plenty of sampling frequency, just not enough discretization. The F45 sensors looked attractive because of their shorter stroke but it still wouldn't be enough I don't think. I need higher resolution. Oh well.....
Thanks for the info on the Race Technology wheel speed sensor converter. I hadn't seen those and will look into them a bit.
I've thought about splicing into the Manifold Air Pressure sensor but I'm not sure what I'd do with the info. I'm not looking for max horsepower so intake development isn't really of interest to me. Intake air temp might be interesting.
I have been playing with IR tire temp sensors. That's my newer "toy." I've had rear sensors for while but just added fronts. I was logging accusump activation while I had one but have since dry-sumped. Thought about adding a pressure sensor to the oil pan to log vacuum. It would be more for engine health monitoring. Trans and diff temps are logged as is ambient temp. These temps are done with non-factory sensors that I've added.
As you can tell, most of this is for fun. There are some good books on data interpretation and it has been fun learning.
Last edited by MySR71; 06-24-2016 at 08:01 PM.
04-16-2017, 10:32 AM
#20
Burning Brakes
I'm in the process of using an Aim MXG as my stand alone dash. That being said, this article has been very informative but I was wondering if someone had the calibration formula for the stock ECT (engine coolant temperature ) sensor? I don't have a stock gauge to take measurements with and don t feel like using an infrared gun on the radiator tank to approximate.