Hello,

Reading the datasheet of the LM , the input needs to go negative , wich does not happen in your case.
You could try to use a resistor of 10K from the input of the LM to ground and a capacitor of 0.1 uF between the input of the LM and the output of the sensor.

Bertus

 

YES , this did the trick
But now have other issue, actually 2

1 - max voltage is about 0.38V, how can I calculate some other values of the components to get max voltage around 5V ?
2 - if I stop the wheel and the sensor is not in hole, I get 0.01v on the output, but is I stop the wheel and the sensor is in hole I get around 2 - 4v very osculating... shouldn t I have 0 as long as I don t have any move?

Thanks a lot

 

Hello,

For issue 1 , have a look in the datasheet at page 7, where you can find the formulas.
For issue 2 , when the sensor is looking in the hole, I would expect a high voltage.
You will likely see the oscilating due to ambient light.
Shield the ambient light and see what happens.

Bertus

 

I did again first schematic tried (attached) and applied your trick with resistor and capacitor and works perfectly I think
I will do more tests now

Thanks a lot

 

The LM2907 and LM2917 are very good tach devices, to get the input to work you can add a series capacitor to get the zero crossing. But at one pulse per second you will not get much. Use a gear with a fairly fine pitch and get a much higher frequency and the circuit will work much better.

 

Hello,

Why don't you use a direct frequency measurement with the arduino?
Here are some examples:
https://tushev.org/articles/arduino/9/measuring-frequency-with-arduino
https://www.arduino.cc/en/Tutorial/SimpleAudioFrequencyMeter
https://circuits4you.com/2016/05/13/arduino-frequency-counter/

Bertus

 

Just curious, you are trying to measure speed, pulses/sec, but using a technique
that simply complicates by translating that to V which in code you have to reinterpret
to pulses/sec ? That also adds error to the measurement.

Prior poster mentioned just measure frequency with Arduio and get rid of all this
extra junk not needed, eg. the V/F converter.

Regards, Dana.

 

Basically you are right but I am doing this for playing and just wanted do it like this. I already did it with pulses on arduino..
Thanks again

 

The LM2907/ LM2917 F/V ics are very good products that I have designed into several instrumentation systems. Of course, it is a requirement that they be used within the intended design range, which did not go down to the 1 pps input mentioned earlier in this thread. The benefits of the 2917 over any arduino implementations are simple calibration, much lower cost, supply voltage regulation built in, and no need to use an external computer to load in some program that may or not function as desired. In addition the 2917 will handle a large variety of input waveforms, although it is a requirement to understand what it is doing. Like most devices, reading and understanding the application information is very likely to lead to success.