RPM channel only works with PC connected

redparchel · Post by **redparchel** » Thu Nov 13, 2014 6:10 pm

Hello folks,

I've noticed some strange behavior and was hoping someone's seen this before or has some ideas.

My RPM channel only works when I have a pc connected to the RCP and RCP_app v2 open/connected BEFORE turning the car on.

Any other combination does not work. Also the RCP android app will also not report RPM unless the above is true. all other channels seem to be working fine.

thanks!

EDIT: i see a similar issue everyone was working on here: http://www.autosportlabs.org/viewtopic.php?t=4202 but not a resolution. any ideas/

EDIT2: I'm running a 2009 mini cooper, tapped the RPM signal off pin 9 from the OBD-II port, which is a common place to grab that signal for this car

redparchel · Post by **redparchel** » Fri Nov 14, 2014 7:30 pm

tired switching the 'channel operation mode' to frequency from RPM, and this behavior changes, it now displays and logs 'RPM' without hooking up the PC first.

That said the reading is horribly wrong, i guess i gotta figure out the right 'clock divider' and 'pulse per rotation' settings, when it was in RPM mode this was 128 and 2 respectively

Post by **brentp** » Mon Nov 17, 2014 5:14 pm

Hi, We're currently looking in to this.

Are you certain it requires the PC to be connected, or does power merely need to be applied to RCP first before the engine is started?

What kind of signal are you getting from the OBD2 port? what is the voltage / waveform like? is it 0-5v, 0-12v, or something else?

toga94m · Post by **toga94m** » Mon Nov 17, 2014 8:17 pm

I found this forum thread, where someone says they got a clean 0-12V squarewave from pin 9.
http://www.northamericanmotoring.com/fo ... ost1409710

Post by **brentp** » Wed Dec 03, 2014 6:51 pm

Hi,

We're thinking that perhaps the 12v signal is causing a problem with the input circuitry and we would need to limit it to 0-5v. Would you be able to do a test with a resistor and a zener diode to limit the voltage going into the RPM input and tryting again?

The circuit would look like this:

Code: Select all

-----/\/\/\/\/\------X-------------RCP Input
    1K resistor      |
                     | 
                   -----
                    / \    5v zener diode
                   -----
                     |
                     |
                     |
                    GROUND

also described in this image: http://www.reuk.co.uk/Zener-Diode-Voltage-Regulator.htm

Let us know if you'd be comfortable trying this out.

gizmodo · Post by **gizmodo** » Thu Dec 04, 2014 1:19 pm

I have tried everything I can think of to get the RCP to read the 12v signal from my MSD tach adapter. Should I give the above circuit a try?

Post by **brentp** » Thu Dec 04, 2014 3:27 pm

Yes, please do. You can get the parts from Radio shack at a low cost. Let us know if you need help making the circuit.

Do you have a way to visualize the MSD tach signal - such as with an oscilloscope?

gizmodo · Post by **gizmodo** » Thu Dec 04, 2014 7:21 pm

It looks like my local Radio Shack lists a bunch of different zener diodes. I don't see one listed at exactly 5 volts. There are 4.7 volt and 5.1 volt versions. I'm guessing I want as close to 5 volts as I can get without going over, correct?

I don't have anything to monitor the signal, but from what I've read it is a square 12 volt signal. I thought I had this problem fixed with CoilX, but that gave me a lot of trouble so I removed it. Hopefully this will solve my problem.

If you have specific part numbers that I can go to Radio Shack with let me know and I might be able to test it this weekend.

Post by **brentp** » Thu Dec 18, 2014 11:32 pm

Actually, I was able to replicate this by looping back one of the PWM inputs into one of the timer inputs.

So to 100% confirm, this is only a problem when the engine is running *before* you power up RCP? Looks like there should be a firmware fix for this.

Post by **brentp** » Fri Jan 16, 2015 7:14 am

We have a MK1 v2.7.7 pre-release firmware that appears to have fixed the RPM problems at RCP power-up. You can download it here:

http://dropcanvas.com/bthz0/30

If the link above is bad, you'll likely be able to download the official release in the regular downloads area.