For Morse signal detection, I used an NE567 tone decoder IC, and its output was processed by the Arduino code, which displayed the corresponding characters on an LCD screen according to the received Morse code. To avoid having to connect the circuit input directly to a radio, the incoming audio signal is provided by a small electret microphone capsule and a single-transistor amplifier.
Of course, due to the acoustic coupling, environmental noise can interfere with the decoding.
Alright, but how does this lead to 1 Hz?

To avoid having to connect the circuit input directly to a radio, the incoming audio signal is provided by a small electret microphone capsule and a single-transistor amplifier.
Of course, due to the acoustic coupling, environmental noise can interfere with the decoding.
Alright, but how does this lead to 1 Hz?

Well, there are several radio stations around the world that broadcast accurate time signals.
One such transmitter is located in Germany and operates at 77.5 kHz, while another is here in the UK, broadcasting the time code at 60 kHz.
There are also others, for example on 2.5, 5, and 10 MHz — but those are all based in the USA, so receiving them from here is quite difficult.

So, I focused on the 60 kHz British and the 77.5 kHz German time stations.
Even receiving those isn't easy, and on Sunday morning, I suddenly didn’t feel like building a receiver — let alone a suitable antenna.

And that’s where a wideband SDR receiver available online came to the rescue.
Here is the link for the WEBSDR receivers http://websdr.org/

The Dutch SDR receiver http://websdr.ewi.utwente.nl:8901/ covers an impressively wide frequency range — practically from 0 kHz up to 30 MHz. So, I chose this receiver to pick up the signals from the 60 kHz and 77.5 kHz time stations. Both signals are received excellently through the SDR, continuously and clearly, although not without the occasional clicking noise.

I tuned into the transmitter’s signal and adjusted it so that I would get an audio tone of around 800 Hz through the PC speakers. Then, I placed the small microphone from the previously mentioned NE567-based circuit in front of the speaker. Using the 10 kΩ potentiometer in the circuit, I adjusted it so that the red LED connected to the NE567’s output would flash in sync with the 1 Hz rhythmic tone coming from the speaker.

The NE567 PLL locked onto the signal beautifully, and the LED began flashing steadily. I connected an oscilloscope to the output — and on the scope screen, the time-coded signal repeating every 1 Hz could be clearly seen.

And we could say — that's it, something now happens every 1 Hz.
And indeed, it does.

Of course, in its current form, it’s not particularly useful, since the acoustic coupling allows external noise to interfere with accurate reception.
The SDR receiver is also constantly affected by brief atmospheric clicks.
However, these can be filtered out with a microcontroller, and a clean 1 Hz square wave can be generated at the output.

But… that might have to wait until after lunch and an afternoon nap.