Measuring Low Frequencies - Signal Conditioner for Sine Wave

I need an integrated DAC Sensor to measure frequency of a low frequency signal. The signal is a 3-phase sine wave at frequencies of 0-45 Hz. The signal voltage is frequency dependent (0-80 VAC). I haven’t found a signal conditioner that will accept this input range and give me a 0-10 VDC output.

Thought of building a Zero crossing (sine to square wave) circuit with an op-amp and feeding that to the frequency signal conditioner but was hoping that there was a signal conditioner that could measure the frequency of a sine wave directly.

Hello Gopher, welcome to the DigiKey TechForum.
I was unable to find any match to your description. Hopefully one of the Engineers will add their knowledge, and find something you can use.

Something useful might be found in the V/F and F/V converter family, here.

Those aside (many are quite old) I suspect that people are apt to use microcontroller timer peripherals for such needs these days.

Thanks David.

Thanks Rick

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Hello Jerry,

I was going to suggest looking to the industrial control side of the house. DigiKey has a variety of 3-phase monitoring relays.

As an example, consider the first item in that list:

As I understand, this device is capable of monitoring all of your generator outputs. You will need isolation transformers to place your system voltage into the desired range. Also, I believe this product communicates with the Siemens Step-7 line of PLC.


  1. Are you testing products like your VOLTURNUS or are you looking to integrate a small device into the final product. The Siemens may be a good choice for the first but not the second option unless we are talking about your Continental device.

For what’s it’s worth, an Arduino UNO has just enough processing power to monitor a single phase for RMS voltage, current, and phase angle. A more powerful processor should be able to handle all three phases. Unfortunately, as you implied in your note, there are high development costs associated with making your own power monitoring and control device.

Best Wishes,


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Thanks for the suggestion.

Yes this is the type of instrument I am looking for. The problem is the frequency is limited to 45-65 Hz. This is way above where I need to measure.

I will have to add some discrete components to alter my input waveform into a pulse train and use a standard frequency counter signal conditioner.

Your point on the Arduino is exactly our thinking as well. We are looking at the Opto with WiFi if we can for size and power consumption.

Thank you for taking the time to respond.



No worries, Jerry,

Perhaps a low voltage transformer and a Schmidt trigger optocoupler such as this:

Be sure to run the transformer well below design voltage to avoid saturating the core at low frequencies. Also, include a diode clamp as the reverse voltage for the optocoupler is very low.



P.S. I should have specified, that the Arduino was sampling both the current and voltage waveforms. As I recall the limitation was the speed at which the ADC could switch and sample.

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Good advice, thank you Aaron.



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