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By melvinvdb
Hi All,

So I've finished creating my engine loom and the car is running and idling on Speeduino :)
I do unfortunately have sync issues at 2000-2500rpm and 4000+ rpm. The rpm goes like crazy and sync is lost.
- I'm using a Ford zetec VR sensor on a 60-2 trigger wheel.
- Using the v3 conditioner with 4.7K 3w R10 resistor (also tried without).
- Set trigger edge at RISING. Not using a filter yet.
- I'm using this shielded cable: https://www.aliexpress.com/item/5M-24AW ... 4c4d3E77Uk. Is it a bit thin but that shouldn't be an issue right?

Below is a few pictures of my oscilloscope connected to conditioner input and output pins.
First question: Is the VR polarity correct? The MAX9926 is a reverse type...
I do have a air gap of around 1.5mm.

I still have options left of trying filters but currently I have to many questions like the polarity, cable used and air gap.
Any help would be very appreciated.

By turtana
what code are you running ? load your code from the github master or use the speedyloader to get the latest bug fixes.
By turtana
i think you have the polarity or rising/falling the wrong way. please post your tune.
both of my vr boards the maxx9924 and v1124 use rising on the trigger edge.

this is the composite trigger view that you want with rising setting, my wheel is 12-1 but you see the pattern.
speeduino rising.jpg
speeduino rising.jpg (447.77 KiB) Viewed 3616 times
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By jonbill
1.5mm is quite a big gap between sensor and teeth. I have a zetec vr sensor too and can get a sheet of paper between mine. I'm sure I read this is what the target is.
By noisymime
With the MAX9926 based conditioners, you definitely want the trigger edge to be FALLING, not rising.

The cabling could be a concern, particularly given it's unshielded. VR sensors really should have a shielded cable between them and the conditioner as they can be very sensitive to noise.
User avatar
I'm a bit concerned that your conditioner output is not a relatively clean square wave that most conditioner modules are known for. This is especially concerning for the sloped inverted output.

For reading VR signals on missing-tooth wheels there are several good references, and this is the first one I pulled-up on search that describes both the intended VR polarity (sensor V+ rising as a tooth approaches) and the tooth edge we look for (falling as the tooth departs): VR Interfacing Because the MAX992x inverts the signal (outputs rising signal on a tooth and sensor falling-edge), Speeduino must be set to the opposite of the edge you are actually trying to detect. Use care when reading or planning for which "edge" you are examining — the physical tooth edge, the sensor signal edge to conditioner input, or the conditioned output signal edge to Speeduino. ;)


From the MAX992x datasheets, you can see that the output follows closely at high rpm, however the output drifts retarded versus the input leading edge at lower input speeds. While different VR modules will exhibit different traits; this is another reason we prefer to detect the tooth falling/output rising edge with the MAX. However, your 'scoped signal indicates a divergent sloped output signal, introducing a new variable:
MAX992x_INvsOUT.jpg (171.92 KiB) Viewed 3589 times
By melvinvdb
Hi David,

Thank you for the explanation. I haven't looked at the polarity yet but first started tackling the bad digital signal.
In the previous posted picture you can see a rise time of around 200us at 2000rpm (2khz*60=120000rpm/60tooth=2000rpm). That is pretty bad. So I've connected my phone to a stereo amplifier with a tone generator app set at 6000hz.
This is the result:
As expected the voltage doesn't go above 3.2v which almost doesn't saturate the atmega pin. Than I removed capacitor c25 which is a 0.01uF cap:
There you go problem fixed. Voltage is a bit high though (5.52v).
I don't understand why there is a capacitor at a digital input signal? The cap will result in a drift in trigger as the rpm increases because it wants to charge.

Also previous I fixed another PCB issue which I should mention for other people. I'm using a hall sensor with single tooth for the secondary input (have disconnected it for now until all issues are solved). This input also didn't work properly because the hall sensor wasn't able to properly pull the signal low (JP5 pull-up is connected). This was caused by the MAX9926 VR2 output pulling the line low even after switching JP3 to HALL.
The input for secondary trigger is always connected to the MAX9926 second output so the only solution was to remove the output pin (pin7 in 0.4.3 schematic) of the conditioner PCB.
This is something to place in the manual because people without an oscilloscope will be troubleshooting this for days otherwise. When using a hall sensor make sure you do not solder/connect the conditioner output pin.
VR1 output pin: pin 8
VR2 output pin: pin 7
User avatar
That appears to be good analysis and at least a partial solution. I would suggest it be determined the best course(s) of action (best solutions) before advising users in-general, and about which board design(s) or BOMs, at this moment.

For example (and without testing this myself), an unused VR2 channel with a MAX conditioner might be acceptable if the VR2 input is pulled low, for a high output, which would act as the pullup for Hall sensors? E.g., for VR1=VR and VR2=Hall, set jumpers for VR and Hall, and no pullup on the Hall (MAX high output does the pullup). Something like that or other option without hardware mods other than deleting/altering input capacitors?

During this quest, better or best input options will likely be determined to apply towards future board or revision designs and their input configurations.

By pazi88
I think you still have something wrong in your vr-conditioner or circuit. On my tests, I have had perfect 0-5v square wave out of the max9926. Not oddly shaped one like yours. Max should just pull down the signal wire, and the pull-up resistor raises the voltage to 5v when maxx doesn't ground the signal output. So where that more than 5v comes from is really strange.
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