HELP - Square wave to sine wave converter project 1

[kidturbo]

Newbie here looking for some help on a small circuit project. Trying to find a company or individual that can do a small run of "black box" speed transducer signal converters.

I need to convert hall effect square wave output from a 3 wire speed sensor to a sine wave pulse for a 2 wire high/low signal used in automotive a ECM environment. After plenty of searching for existing converters nothing jumps out at me. I believe it's a zero crossing detector circuit that's required, like available in the MOC2A60-10 Amp Zero Cross Triac Output IC. However my computer skills only help me find what I might need, not build it...

So any suggestions on where to contract out this little build would be a great help.

Many Thanks

-K

 

[ScottyUK]

If you don't mind a bit of playing about the following EDN article might be an interesting starting point.

http://electronicdesign.com/article...-circuit-converts-square-waves-to-sine-w.aspx

http://archive.electronicdesign.com/files/29/9493/figure_01.gif

It's one of those interesting ideas I've bookmarked but never tried out yet - I'd be interested how you get on.


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If we learn from our mistakes I'm getting a great education!

 

[VEBill]

Depending on the particular application (engine speed vs. crank position), one should carefully consider the maximum acceptable phase shift requirements.

 

[kidturbo]

Thanks for the suggestions.

In this application error rate is not super sensitive, mainly going to be used to calculate fuel mileage in boats. All the marine type speed senders are all effect, while the automotive ECM's use inductive pickups.

The ECM doesn't require a speed sensor to operate, but can calculate fuel mileage if it knows ground speed. Calibration can be done on the ECM once you know a pulse per mile figure.

-K

 

[IRstuff]

Here's another option, albeit more complicated than the one's already posted:

http://forums.parallax.com/showthread.php?123791-Propeller-mediated-Sine-Wave-Frequency-Synthesizer

It's sort of a PLL, using a sine wave generator whose control input is mediated by a comparison of the square wave and the generator output.

Another option is hinted, at the bottom of the article, which is to do a direct digital synthesis, which can be a look-up table running into a DAC, driven by a PIC that's measuring the period of the square wave and then timing out the sine wave's digitized output. Make the DAC output sample frequency sufficiently high, and you can use a simple lowpass filter to get rid of the quantization noise.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[vangjer]

alpha-beta transform

 

[bradrs]

This may be a silly question, but why do you need to convert it to a sine wave? If the automotive ECM is just looking for a number of pulses, and you seem to think error rate is not critical, why does the shape even matter?

I've seen square waves used in place of sine on several vehicles, with no problem. I'd try just scaling the frequency to get where you need, and possibly do a level shift on the signal to get the trigger levels right. And then since its automotive, spend more time making sure its robust enough to live in its environment.

 

[Comcokid]

I go along with Bradrs comment. If the automotive sensor used with the ECU is typically an inductive pickup, then it is only looking for zero-crossings anyway, probably with a simple comparator circuit internally, or a little filtering into a transistor switch.

Now, inductive pickups have a 2-wire AC output. If one wire is grounded, then the signal in the other wire goes both above and below ground. Your hall effect signal will probably be a square-wave from about .6 volts to about 12 volts, but it doesn't cross zero. Probably the only thing you need to do is take the Hall-effect output, go in series through a capacitor (non-polar, of maybe a film type of maybe 1 to 10uF, of about 25 volts minimum) to the ECU input. This will block the DC component of the Hall-effect output signal to give you a signal that goes above and below ground.