# 75hz relay circuit

Hey, I'm trying to make a project that will close a relay when I will send it a 75 hz tone (the kind of signal that a line tracker uses).
When I tried to measure it with fluk multi meter its gave me a really low ac voltage (0.5-3vac).
How do I uses this to notify my arduino? like turning it to dc or am I on the wrong way of thinking

I really don't know how this signal works expect the theory of waves (modulation and etc) so I don't know how an arduino can sense it.

When I tried to measure it with fluk multi meter its gave me a really low ac voltage (0.5-3vac).
How do I uses this to notify my arduino? like turning it to dc or am I on the wrong way of thinking

Is this the signal to the beeper? It's possible that it's pulsed DC...

I really don't know how this signal works expect the theory of waves (modulation and etc) so I don't know how an arduino can sense it.

That's where things get "dangerous". The Arduino can be damaged by voltages greater than 5V or by negative voltages, including the negative half of an AC waveform.

It would be a good idea to use a [u]protection circuit[/u] to the Arduino's input.

If the signal turns-out to be capacitively coupled, you may also need a 10K pull-down resistor between the Arduino's input and ground. (The pull-down will prevent the input from floating and give you a solid low/zero when there's no signal.)

Use an analog input and run the [u]Analog Read Serial Example[/u] to see what kind of readings you get. Since it's a "signal" and you're reading at random points along the waveform you'll see some somewhat-random readings. But, there should be a clear difference between signal and no-signal.

Once you know what you're looking for, you should be able to use an if-statement (if reading > X, etc.) to decide if a signal is present.

P.S.
Not important - But, the tone probably isn't 75Hz, which would be a low "bass" tone (with harmonics, assuming it's a square wave).

Tone Decoder

The LM567 and LM567C are general purpose tone decoders designed to provide a saturated transistor Resistor switch to ground when an input signal is present within the passband. The circuit consists of an I and Q detector driven by a voltage controlled oscillator which determines the center frequency of the decoder. External components are used to independently set center frequency, bandwidth and output delay.

Thanks
I looked at that ic and maby its what I need !