Corvette CCM Reverse Engineering Anyone?

[spfautsch]

Oh, no no, don't take my reply the wrong way; I was in no way being critical of your code

Not taken that way at all. Just making sure we're on the same page. I wanted to push the timing envelope while servicing other devices in the main loop and that required a hardware timer.

As for your latching relay thing, I was thinking of handling it without one. I mean with a latching relay you can go to completely 0 power draw, I agree, but the power draw of an Arduino-based chip in full sleep is what, 10 microamps or something? Why not just set an interrupt for the RX pin going from low to high to wake it

Tried that and it does work. But the SD card in particular, the miscellaneous smc leds and the dual voltage regulators on the mega board draw a lot - 75ma in idle mode according to my best meter with all but uart1 (ALDL) turned off. Not worth designing my own board so I'll just flip the breaker after the CCM goes to sleep. It adds some code and component complexity but the last thing I need is to trade convenience for more parasitic draw on the battery.

As always life happened today so didn't make as much progress as I'd hoped to. Still need to resolve an occasional CCM timeout after killing the ignition (and power to the PCM).

[NomakeWan]

Have you tried shutting down all the ADC registers before dropping into sleep? Apparently just using

ADCSRA = 0;

reduces power consumption by three orders of magnitude. It'd be like Sketch J here: http://www.gammon.com.au/power

Apparently that sketch on a bog standard Arduino draws only 0.15 microamps while sleeping, which is two orders of magnitude less than I thought. Should work on the Mega.

[spfautsch]

Nick's examples were done using a 328p on a custom board without voltage regulators, leds, peripherals, etc.

The mega boards have two voltage regulators, one of which I believe is linear and therefor very inefficient. According to this [link] the lowest power consumption it's capable of while using the on-board regulators is ~27 ma. That's with the adc turned off and processor in PWR_SAVE mode. Meh. Add on the logger shield and sd card and it uses even more power.

Was able to clean up a few issues and it looks like latching relay will work as planned with the possible exception of key in + key on after the CCM has gone to sleep. But I don't generally sit in the car with the door closed without the key in the ignition.

[NomakeWan]

Ah, fair enough. Guess it's yet another thing for me to experiment with on my own. I enjoy that though so, hey!

It took me a second to figure out why "key-in+key-on after CCM sleeps" would be a problem, then I remembered that the logger was being triggered from the courtesy lights. Considering the use case for this device, I highly doubt that will be an issue. An errata to make sure to spell out in documentation, sure, but I think anyone who would have one of these left plugged in is going to get in and out of their car for drive cycles.

[spfautsch]

SSRs showed up a few days ago and I have the completed system ready to go in the car. The "joys" of x-mas shopping with the wife took up today but I hope to get on it tomorrow.

What is this "documentation" you speak of? ;-).

[spfautsch]

Here's a very, very rough beta release.

aldl_logger-0.9.4

Project page here [click].

Discovered that the analog 5v regulator on the mega wasn't quite up to the task of powering all the uarts and leds while writing to SD with 14v input so added a 7805 and powered the 5v rail directly instead of the Arduino's VIN.

The latching power relay seems to work as well as could be expected. The only high-priority change I anticipate adding is a long-term timer to shut power off to Arduino after no CCM / PCM / datastream sync. Currently it closes the open files on the SD after logging data has been written and the CCM has stopped broadcasting. Sometimes this is as short as 5-10 seconds after closing a door without key in ignition.

This is a very roughly crafted beta release. Almost everything needs to be fine tuned, but it seems to work as intended. Writes PCM data from the ALDL to a .eedata file, diy-ltcc logging to a .log file, and it's own debugging information to a plaintext .dbg file.

kur4o if you're interested in something like this for the F body keep it in memory. There are a lot of design decisions I made with this that hinge around the CCM being bus master and having to silence it and then seamlessly hand master back after the PCM goes to sleep. It's certainly possible to make loads of conditionals to handle the differences, but it also might make more sense to fork a different firmware.

[AngryCorvair]

i know this thread has been dormant for a while, but after a couple years of lurking and learning on this forum i finally think i can contribute something.

I bought a 94 Corvette in Jacksonville FL and drove it home to Canton MI with absolutely zero issues. Then, like you do after a trip like that, I pulled that car apart as a donor for my mid-engine '65 Corvair project. I kept the entire electrical system from the C4, including the CCM. If one of you could use it to further the R&D, i'd be happy to send it your way, for $free, and i'll even cover shipping. PM me if you could make use of it.

Donor was automatic with 2.59 rear. I've got a pic of the options sticker if that would help.

Regards,
Patrick