C125 Aux Output for Tachometer

[01-0041]

All,

I’m in the planning stages for my C125 and would like a bit of help.

I’ll be using the C125 in a US spec ’95 E36 M3 (OBD1) that will be eventually be running either an M130 or M150 depending on how I can utilize channels.

Of the two options; which of the following “Duty Cycle Control” or “Frequency Control” would be best for an RPM output - signal for factory tachometer - of no more than 8000 rpm and what’s the best method for setting it up once I load the "M1_General" CAN list?

Thank you for your time!

[Stephen Dean]

Hi,

Are you wanting to drive the factory tach from the C125, or read the data that is going into the tach into the C125? Do you know what sort of signal is used by the standard factory dash.

The C125 has support for OBD-II compliant cars, and does not have support for the earlier OBD systems, so it is most likely that you will not be able to get any data into the C125 from the standard factory ECU, unless you piggyback the signal wires for the sensors.

The M1_General CAN template is a specific template that is designed to work with the CAN messaging stream that is output from the M1, this will only work with the M1, and not other ECU's

[stevieturbo]

Can the ecu not just drive the tacho ?

[David Ferguson]

I have used frequency control to produce a tachometer signal (for a Paddle Gear Shift Controller). Depending upon the tachometer input, you may need to provide a pull-up resistor (try 10k as a starting point) to 5V or 12V depending upon the needs of the sensing device.

I had to play with the duty cycle to get a signal that made the Gear controller happy. Turned out to be 75% duty cycle. My setup was:

Output Mode: Frequency Control
Frequency Channel: RPM
Channel Value for frequency of 0 hz: 0 rpm
Channel Value for frequency of 1000 hz: 60000 rpm
Duty Cycle: 75%

This was simulating a motorcycle engine that normally produced 1 pulse per engine revolution. For a 4 cylinder / 4 stroke, you probably want to use 120000 rpm (if a 6 cylinder, then 180000).

Hope that helps.

[01-0041]

Hi,

Are you wanting to drive the factory tach from the C125, or read the data that is going into the tach into the C125? Do you know what sort of signal is used by the standard factory dash.

SD,

I'm looking at driving the tach from the C125. The factory signal is a frequency based input. I was able to figure out most of what I need until I have a chance to test it out.

Thank you.

[01-0041]

I have used frequency control to produce a tachometer signal (for a Paddle Gear Shift Controller). Depending upon the tachometer input, you may need to provide a pull-up resistor (try 10k as a starting point) to 5V or 12V depending upon the needs of the sensing device.

I had to play with the duty cycle to get a signal that made the Gear controller happy. Turned out to be 75% duty cycle. My setup was:

Output Mode: Frequency Control
Frequency Channel: RPM
Channel Value for frequency of 0 hz: 0 rpm
Channel Value for frequency of 1000 hz: 60000 rpm
Duty Cycle: 75%

This was simulating a motorcycle engine that normally produced 1 pulse per engine revolution. For a 4 cylinder / 4 stroke, you probably want to use 120000 rpm (if a 6 cylinder, then 180000).

Hope that helps.

David,

Thank you for the information.

I came up with the following:

Output Mode: Frequency Control
Frequency Channel: Engine RPM
Channel Value for frequency of 0 hz: 0 rpm
Channel Value for frequency of 1000 hz: 20000 rpm - 6 cyl with interpolated value based on four data points.
Duty Cycle: 100%

I'll need to play around with duty cycle once I get to that point, but with your information and my sampling the car this weekend I have most of the information I need.

Doing this allows me to free up one output channel on my ECU.

Thank you!

[David Ferguson]

Well the duty cycle can't be 100% (that would be on all the time regardless of the frequency). I suggest you start with 50%, then try things like 20% and 80% to see which it likes.

And you're right on the RPM at 1000 hz. I got that backwards. 4 cyl/4 stroke should be 30000, and 6 cyl/4 stroke would be 20000.

[01-0041]

Well the duty cycle can't be 100% (that would be on all the time regardless of the frequency). I suggest you start with 50%, then try things like 20% and 80% to see which it likes.

Will do.

Thank you for your time!