Variable Reluctance input

[AndreyB]

Which VR driver should we use?
LM1815 - this one is available in DIP case - cost is $3.5
MAX9926UAEE - this one does not have a DIP case and this one is closer to $8
NCV1124DGOS - again no DIP case but this one is $2.5, seems to be the cheapest one

Are they all the same? Is there any significant difference? Should I start with LM1815 just because I can play with it on a breadboard?

[erich]

The Maxim IC is fancy, and only available in fine pitch surface mount. It'll be a total bear to solder by hand.
The ON chip is simpler and a dual VR amp, with .050 lead spacing which is easily doable by hand.
The big difference between the TI chap and the ON chip are the outputs.
The TI chip outputs a fixed length pulse percycle, the ON chip outputs a more or less square wave from a sine imput.
Seeing how this will be used with a toothed wheel or a missing tooth setup I don't think it makes much difference except on where the physical cycle starts in relationto the electrical output.

[kb1gtt]

I can't seem to find the comparison right now, but some where the LM1815 and MAX9926 were compared against each other. The MAX was better as it's reaction time allowed for a detection of a skipped tooth wheel at low RPM. Basically the LM1815 didn't auto-calibrate quickly enough so it failed to detect properly. Also the max chips has a much better Common Mode Rejection, which means noise from bad grounds, or ignition RF will influence the VR signal much less on the MAX than it will on the LM chip. The MAX is very small, so soldering it up is a bear. Also you have to be careful with the pre-made boards, as they have a good chance of dumping high voltage to the 5V rail, which can be bad. JBPerf's Dual VR 2.0 board was much better than the current 2.1 revision. I know the MAX can be configured to work as either VR or hall, I don't know if the other chips can be configured that way.

I don't know much about the on-semi chip. On a quick look over the datasheet, I think it's better than the TI, but not quite as good as the MAX.

[kb1gtt]

Ah here we go, found the link http://www.miataturbo.net/diyautotune-miata-accessories-30/over-19-000-rpm-bench-test-60325/page2/#post771472

Money shot picture below, the yellow trace is the output of the LM1815 notice the missing pulse, when it should have pulsed.

[AndreyB]

So it has to be MAX but we cannot solder MAX by hand?

Is there maybe something solderable AND efficient?

[kb1gtt]

http://jbperf.com/dual_VR/v2_1.html#Buy

I prefer the 2.0 board as that was a better design, however this will work for most people. I'd recommend good over voltage protection on the 5V. I had a good explanation on a forum once, however the forum admin deleted that some time ago.

[AndreyB]

http://jbperf.com/dual_VR/v2_1.html#Buy

Right, that would be an option for now, but at some point we need to put this on our own board, right?

[kb1gtt]

That is drafted in the IO board I made so we have that in KICAD already. It's should be minimal work to integrate that on a board.

[kb1gtt]

http://rusefi.com/forum/viewtopic.php?f=4&t=227&p=914

From the above link, that thread has a broken link in my post. See the 4th post down, which was by me. It appears that the below picture link is no longer pointing to an image, which no longer shows in the thread. The original miataturbo.net thread is also broken.

Code: Select all

http://img401.imageshack.us/img401/9299/1815real14rc1mmgap1666rws8.gif

Getting that picture back would be really handy.

[AndreyB]

I do not have a copy of that picture, does anyone?

Can not trust the internet, need to always download, attach and link source to be nice I guess.

[Rhinoman]

You need to study the circuitry as well, problems with VR sensor interfaces are usually down to poor PCB layout, insufficient decoupling or just putting too much current into the inputs. I've seen some terrible analysis of theses chips, including one that was done on a breadboard!
What speed were these tests done at? they are talking of speeds around 17k RPM.

[kb1gtt]

I recall the failure was at low RPM. With some luck, we'll get that scope capture back and then we'll know what RPM that was done at.

I recall the issue was very similar to the MAX992#'s 88mS self setting gain loop. I recall the LM1815 had a much shorter time for this, which caused it to loose sync at low RPM on a 36-2 wheel. While the MAX chip looses it on a much larger gap, I recall this chip was loosing it at a 2 tooth gap with around 500 to 1k RPM.

I've also seen some crappy designs. The VR can reach very high voltages, which cause stray currents. I've seen these high voltages routed very close to the 5V pin. What better way to make sure your entire ECU is a brick than to put 300V on your 5V line. Yup, in my opinion that design is intended to make your ECU a brick instead of an ECU.

[puff]

are you referring to my design? %-)
isn't the input at max thing somewhat close to 5v line too?
i doubt very much that it would reach 300v in a car. though, i'd say 300v on a hi-rev moto engine is quite achievable..

[kb1gtt]

What is your design? I might be referencing your design, but I think I am not. If it's your design I can make some suggestions. Also see spread sheet calculator I made found here.

http://rusefi.com/wiki/index.php?title=Manual:Hardware_Trigger#VR_lower_level_details.2C_formulas.2C_app_notes.2C_etc

[puff]

If I am not mistaken, my board is made using these files:

Снимок экрана 2017-04-06 в 19.25.49.png (43.17 KiB) Viewed 12942 times

Снимок экрана 2017-04-06 в 19.26.13.png (37.33 KiB) Viewed 12942 times

I decided to make it flexible, but as a matter of fact, it is somewhat hard to remember, what do all these pins and jumpers mean...
Hope to hook a scope to both input and output of this board in May to check it at cranking and at 6K...
It's not that easy to put in my head that one of the sensor's contacts is connected to ground. On the one hand, it goes below zero on the sensor, on the other hand, it is connected to ground of the board (which means it is either pulled up to zero or down to zero depending on the part of the sine wave?

[kb1gtt]

Your board is not what I had in mind when I commented about a brick. Yours is not as bad as the brick I referenced. You at least have one 0805 with a working voltage of about 150V. You should consider changing R2 such that you have at least 2 in series. This will spread the watts around and it will also give you closer to a 300V stand off voltage.

I'm not sure I know your primary chip. Is that a LM1815?