2 Frequency inputs -> 1 Summed output

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi,

I have 2 frequency signals (square wave 0-5V) and want to output another frequency signal that is the sum of both.

I want to use 2 airflow sensor on my car because I have 2 turbos (lucky me... :P). Currently there is one air flow sensor, but this isn't very good because it requires some interesting intake pipe work to split the air flow after going through the sensor.

What I want to do is use 2 sensors so that I can run one off each turbo and then sum the sensor output so that I can retain the standard ECU control.

I foolishly thought it should be fairly easy to do... Either it isn't or I am using the wrong search criteria in google :stuck_out_tongue:

I was hoping I could use my Arduino to acomplish this task, however I am at a loss as to how to do it. well, not quite at a loss, but not sure I can actually do waht I want.

My inclination would be to have 2 interupts, which count pulses. Run a timer that triggers at just over 2x the max frequency to be seen (4kHz is the max output from the sensor) and do some calculations to work out what the output frequency should be (again, this shouldn't go above 4kHz)

I believe that should be fairly straight forward, but the bit that bites me is how to output a reliable frequency?
Also, how can I ensure that I get a reliable count from both sensors? What happens if by some fluke the both trigger an interupt at the same time? Or with a 20MHz chip is this going to be so infrequent as to make it irrelivent?

Any suggestions?

2

guessing its a GM type, karmen, http://www.autoshop101.com/forms/h34.pdf http://www.wellsmfgcorp.com/pdf/Counterpoint3_2.pdf

Two ideas
#1, get a map that uses a linear resistance output (GM makes a couple of cheap 2 bar units)

Measure each of the 2 analog voltage inputs, sum them through a special formula, and apply the conversion to freq (DN030 - Frequency Synthesizer
http://www.avrfreaks.net/modules/FreaksFiles/files/417/DN_030.pdf
)

#2 measure both freq's, add with some special formula, combine back into new freq (freq_out)
(not that i've tried it)

Freq_Out= Scale_Total* (Scale_1Freq_Sensor1 +Scale_2Freq_Sensor#2)

KnockSensor (how to calculate sensor 1/2 freq)

DN030 - Frequency Synthesizer
http://www.avrfreaks.net/modules/FreaksFiles/files/417/DN_030.pdf

lastly, i'm working on a 3bar map signal--> converting to 2bar map (w/map clamp) that autotunes based on the wideband 02 input, TPS, and knock_count. my analog prototype works great, now for the Ardunio version -- still having problems with the 4x20 lcd..

3

Thanks for your reply.

I am using a Mitsubishi sensor, I think i'll have a look at #2 first and post the results.

I am very interested in your auto-tune stuff, as this was where I wanted to head next.
My intention was to use the wideband to create a modification lookup table (RPM/TPS/Freq) that is used to condition the frequency output, this table being continually refined by the wideband response.

I didn't intend to use knock, hadn't thought about it :-[ It is definitely a good idea though.