How can I make a reliable tick tock sound electro-mechanically?

Question

I'm hoping to help someone make a metronome-like device, but it'll tick like a clock once per second, all of the time. I was wondering how to produce that sound in a reliable way. There are 32 millionish seconds in a year, and I hope our thingie will last a bit longer.

1. The obvious way is to use a large relay, and pulse it at ½ Hz. That said, I read Electro-mechanical relay durability curve and it caused me to fear that a relay probably wouldn't last, especially not a big one that makes a decent ticking sound.

2. The next thought was a speaker cone, but they don't really make any noise unless actually vibrating making a 'ticking noise' from an audio recording.

3. Solenoid hitting something? Probably less reliable than the relay option.

There will be an Arduino inside the thingie. So, please?

Surprised no one hass spotted my deliberate mistake :-) A large relay clicking upon closing and opening, one tic per second, is powered at ½ Hz not 1 Hz.

Answer 1

If you want something simple, just send a pulse to a speaker. My ancient DIY Geiger counter basically did this. You won't have much control over the sound, but it may be sufficient for your needs.

You probably should put a big cap in series so you don't send any DC to the speaker.

Answer 2

The obvious way is to use a large relay, and pulse it at 1 Hz. That said, I read Electro-mechanical relay durability curve and it caused me to fear that a relay probably wouldn't last. Especially a big one to make a decent ticking.

The biggest factor in relay lifetime is actually contacts switching with load, and supply leads bending. If you ignore that, and only want the ticking, the relay has really few movable parts, and doesn't wear out easily.

From the curve you posted, that device is rated for at least ten million operations under no load. That's 2777 hours of ticking at 1Hz. My bet is that the device operating under no load would survive for at least twice that.

Answer 3

• WWV transmits a "ticking" sound as five cycles of a 1000 Hz sine wave.
  
• WWVH transmits a similar "ticking" sound as six cycles of a 1200 Hz sine wave.
  

When reproduced linearly into a loudspeaker, these bursts might satisfy. When alternated, they may sound like "tick", "tock".

Be aware that average should be zero. That is, the positive peak of the sine wave should extend above zero just as far as its negative peak extends below zero. A web search reveals recordings of these one-second ticks from WWV, WWVH radio stations.

---

Edit: OP considers square wave rather than sinusoidal waveform:
Inverting buffers might be used to drive a loudspeaker with 1kHz square wave. Average of zero is met by balanced drivers having opposing polarity. Tri-state input is used to idle between "ticks" with no power delivered to loudspeaker:

^{simulate this circuit – Schematic created using CircuitLab}

Answer 4

If you want to use a relay as a clicker, you should test it, since the way you plan to use it is not within any specifications usually. Sometimes, relay manufacturers specify the mechanical life of the relay as a separate line in the specs, but it's not very common.

The "relay life" specification is usually called "contact life" and only applies to contact resistance staying below the maximum limiting value given in the datasheet. It does not mean that the relay will mechanically fall apart anytime soon!

Other answers suggest that the mechanical life may be, say, 2x the contact life at rated load. My experience is that without the contacts loaded, most relays will last an extremely long time - orders of magnitude longer than the contact life. As an anecdote, I have tested NEC's now-obsolete MR62 series relays, rated IIRC for a million contact actuations, and got tired of the clicking after they were past a billion cycles. They sounded just as good, and there was nothing obvious that would indicate that they were ready to fall apart.

And finally, the sound a relay makes depends on size and specific mechanical design. Some relays sound fairly similar upon both opening and closing, some have a distinctive tick and tock sounds. For small relays - say 2cm^3 or less - the sound is quite similar on either opening or closing, so indeed 0.5Hz square wave drive will give proper results.

For maximum coil life, the drive current waveform should have a peak value high enough to produce a satisfying click, and a hold value that's a couple times lower than the peak, to minimize the coil dissipation. A simple way to achieve that is to power the coil through a parallel R-C circuit.

"Clicker" applications that demand long relay life should drive the coil with a voltage source of a roughly fixed ON and OFF impedance, i.e. with an actual square wave waveform, so that the coil never "sees" an open circuit. This minimizes the voltage stress on the coil. In practice, this means a push-pull driver stage, e.g. one half of an H-bridge.

Answer 5

Maybe you can find one of the older mechanical Accessible Pedestrian Signal generators, the ones that make a slow/fast ticking sound at pedestrian traffic lights to help the blind. They are loud and last a long time. No idea if they are/were an international thing, though.

Or a ratchet or a ratcheting socket wrench with a stepper motor attached. Or an older, mechanical car indicator light, um, driver.

Or, if it doesn't have to be mechanical, just play a sample in a loop over a speaker.

Answer 6

You could use a $2 voice recorder IC such as ISD2360, and record whatever sounds you like for the tick-tock.

There are others that should work as well. Or you could just copy a digital sound recording into an EPROM and play it back.

There are some complex sound generator and synthesizer chips like SN76489, SN76489, and SN76495, although they may be hard to find. They were used in arcade games for sounds like sirens and machine guns. The UM3561 was specifically for those.

Here are some projects: https://www.homemade-circuits.com/make-single-chip-programmable/

This might help: https://arduino.stackexchange.com/questions/30882/mini-voice-recorder-for-arduino

I found one on AliExpress for 50 cents. I'll leave it up to you if you want to go that ultra-cheap route.