Internal Combustion RPM Sensor

Hardware Other Hardware
1

Hi,

I have a 2-stroke internal combustion engine. The engine already has a sensor in it for the crank sensor and the spark plugs. Its a dual ignition engine so it has 2 spark plugs, 2 ignition modules, and 2 coils.

I have been trying to get RPM working on it and so far I have had no luck. From what I can discern, the engine has a magnetic pickup on it, so it gives a sine-wave sort of output. Is there any way I can use this signal to get RPM? I am picking the signal up directly off of the crank sensor, and it only has 1 crank sensor. I have already tried multiple ways and so far I have had no luck. I have been able to condition it in a way that completely eliminates the negative side of the signal and only gives the positive side, but it still wont translate into the Cube orange+ as a valid RPM signal.

I am using aux pin 3 and have configured it as an GPIO and RPM. So far It hasn’t budged at all in a manner that would suggest anything is connected. It is just sitting at -1 on the data readout.

And help is appreciated.

Below is an image of the scoped output of the crank sensor

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2

If rectified and conditioned to no more than 5V (preferably 3v3), that signal might work with a scale factor of 0.5.

I use a GPIO RPM sensor on my mower’s Cube Orange (AUX2) with the following parameters:
RPM1_PIN,51
RPM1_SCALING,1
RPM1_TYPE,2
SERVO10_FUNCTION,-1

You must use an AUX pin for GPIO input (pin numbers 50-55, which correspond to servo outputs 9-15).

If all else fails, you might try just using a simple 3.3v Hall effect sensor positioned near the magnet on the crank (that’s what I’m using).

3

That looks similar to my setup.

I’m using Aux3:
RPM1_TYPE, 2
RPM1_SCALING, 1 (I can try to tune this. but I have not seen rpm even budge off of reading -1)
RPM1_PIN, 52
SERVO11_FUNCTION, -1

4

Then your issue is electronic, and either you’ve blown out AUX3, or the signal isn’t adequate to trigger the input.

5

The signal shown is not like sine-wave. Can you extract just 1 period and just one spike

Did you tried to put this signal directly to the FC input. If yes than the negative spikes and maybe also positive spikes above 5V can destroy your input pin.
Do you have not only this oscilloscope but also a frequency generator to simulated RPM pulses?

6

Here’s just 1 period.

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I do not have a frequency generator that can simulate RPM pulses.

I’m measuring it at the sensor, When I measured up at the FC input it was more like 2V spikes. I have a diode on it too that eliminates the downward spike

7

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Here’s the actual signal I want to use as an input

8

Can you provide a drawing of your wiring?

9

EDIT (misread the scale - grid lines are faint).

You want a peak between 3 and 5 volts with sharp rise and fall times. 2V might trigger a “high” state depending on the rest of the wiring, but it’s not a great signal.

10

The scale is currently at 500mV per graduation. that one is showing ~1.8V

12

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13

So switching it to AUX2 and reconfiguring parameters. Its still not acting like there is anything even connected. I would imagine there should be some sort of RPM output just based on noise in the system

14

Normally the crank sensor is direct connected to the ignition without the diode?
If so, than place the diode only in the line to the FC
Is you oszilloscope AC or DC coupled?

15

O-scope is on DC settings.

I moved the diode. getting a good honest 2V spike. getting a tiny 250mV negative spike now though.

updated

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DC coupling:
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AC coupling:

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16

Would putting something in like such as this be a good idea?:

And just feed my original signal into it, and then feed the PWM output from that device into the FC?

17

Yes this puls forming stage might be helpfull