Vehicle speed converter

**kirupa** · 03-01-2011, 11:10 PM

Hi..

i want to design a vehicle speed converter for car which takes speed signal from ECU of car and convert it to digital format. i don't have car. i don't know what kind of speed signal come out from the ECU of car. I am an Electrical and Electronic engineer. i have experience developing electronic circuit. I want to know the voltage VS speed waveform diagram of the ECU speed out put. Can anybody help me?

**Bugbyte** · 03-01-2011, 11:20 PM

Any idea what car or ECU model you are designing for? This would probably help people answer your question.

**kirupa** · 03-01-2011, 11:29 PM

Dear Bugbyte,

Thank you for your reply.

Proton, Isuzu cars. is different car use different technologies? I have no idea ECU models.

Thanks again

kirupa

**OldSpark** · 03-02-2011, 01:35 AM

Frequency to voltage is easy enough (LM2907/LM2917), and many speed transducers are pulse types - eg Nissans use a 10 pole sensor on the box (20 pulses per cable rev?) and they can be fitted to (older) Isuzus.

Isuzu often use a reed switch mounted in the speedo (I'm not kidding - and it lasts for hundreds of thousands of miles/km!).

As to digital....

**kirupa** · 03-02-2011, 06:18 AM

Dear OldSpar,

Thank you for your reply.

I didn't get answer for my question. i want to know what kind of speed signal come out from the ECU of car?

1) is this pulse? ( different speed has different frequency)
2) is this linear voltage? ( different speed has different voltage)

Thanks

**whats77inaname** · 03-02-2011, 09:30 AM

Hmmmmmmmmmmm....we don't have Protons stateside. Perhaps you can get a pic of one so we can figure out the corresponding model and go from there?

**OldSpark** · 03-02-2011, 09:42 AM

Originally Posted by kirupa

I didn't get answer for my question. i want to know what kind of speed signal come out from the ECU of car?

Which ECU?

Normally they don't come out of the ECU unless there is a need - and that could be as anything (eg, analog proportional; though usually pulse, coded (binary etc), or discrete/command level (threshholds).

**kirupa** · 03-02-2011, 11:34 AM

Hi..

Thank you for your reply.

Say, now vehicle is moving 20Km/h. i am connecting a oscilloscope to ECU speed output? How will the oscilloscope waveform be? Now i am changing speed to 40Km/h. Now how will the oscilloscope waveform be ?

**Bugbyte** · 03-02-2011, 01:35 PM

It is VERY unlikely that you will be able to design this without having access to the car. Why are you developing this for a car you neither own nor have access to? Is this a commercial project?

**OldSpark** · 03-02-2011, 03:49 PM

Ditto. Again which ECU?

Or answer this:
How will:
- an analog voltage
- a bitsream (hex or binary or BCD)
- PWM or...
- variable frequency pulses
look on your CRO?

Are you using DC or AC input?

Answer the above (at least 4 answers; 8 if AC/DC variation; extra if hex is different to binary)
... and I'll continue.

Also, which Isuzu ECU puts out a speed signal?