Playing with MAX9927, NCV1124, and LM1815

[Peter]

I couldn't find anything very cut and dry about why the MAX is better than the other two. Just stuff about common mode rejection, and a few people who I'm pretty sure have no idea what they're talking about. So I figured I would give them all a test to see if I could even tell the difference between them. I was going to test it tonight, but its about 15F with 30mph wind so maybe tomorrow afternoon when the sun comes out.

My question tonight is: What's the best way to demonstrate the shortcomings of these circuits with an oscilloscope? i.e. Run the engine up against the rev limiter or switch to non resistor type spark plugs.

The max99xx chips are the best of the bunch, but very fine pitched, unless you grab a prebuilt board.

You weren't kidding about the fine pitch.




I think I need to invest in a bigger breadboard. I used 1k resistors for all of the resistors that didn't have values in the MAX datasheet.

[Fred]

There should only be two resistors in your test for the max, ground the config pins such that it uses the internal bias in A2 mode. Gotta go! :-) More later, cool test!

[Peter]

Turns out I didn't need to do anything special to see the difference between the chips. They are hooked up to one of the sensors reading a 6-2 wheel. All of the circuits are based from their datasheets.

The MAX9927. I saw it give me an extra long pulse one time when I was revving it into the rev limiter, but it by far gave me the best results.


The NCV1124. Decent results, but commonly gave me strange looking traces on the oscilloscope. Most commonly one of the pulses would be about twice as long as the other three pulses.


The NCV1124 over a longer time period.


The LM1815 gave me these very short little spikes. It wouldn't let my car rev up so I'm guessing that this chip wasn't playing nice with my OEM ecu and would probably give better results if it was hooked up to its own sensor.


Edit: Grammar errors

[Fred]

Awesome testing! One more question: Why 9927? I guess that's why you have resistors everywhere? It doesn't offer mode A2, and 9926 does. Cool stuff :-) I know someone who will be interested in this testing, linking now!

Fred.

[Peter]

Why 9927?

From the datasheet: "The MAX9925/MAX9927 make all three terminals of the internal operational amplifier available, allowing greater flexibility for gain. The MAX9926 also provides a direction output that is useful for quadrature connected VR sensors that are used in certain high-performance engines."

Mostly because I don't really "know" what the difference is. Also, because when people are talking about them it's listed as MAX99xx, which gives me the impression that they're all about the same. So I decided I wanted a dual version (26 and 27), and I don't have quadrature connected sensors. Which led me to the 27, because it apparently has greater flexibility.

[Fred]

That is true, but greater PCB complexity and the default gain and reference works most excellently. No big deal :-)