4-Minute Shower Timer Circuit Diagram

Gone are the days when we can afford to luxuriate under a hot shower for hours on end. Well, maybe the showers weren’t quite that long but most people are used to taking showers in the tens of minutes. It’s easy to lose track of time in the shower. And it does feel nice.

That’s a luxury that’s no longer economically nor ecologically sustainable. First of all, we’re short of water. In most areas of Australia the powers-that-be keep telling us if we don’t be good boys and girls and cut our water usage then we are going to run out.

(Those same powers [read politicians] that keep blaming us wasteful consumers don’t mention that for the most part water shortages are their fault, because they haven’t invested the necessary dollars in water infrastructure while population has steadily increased for much of the last half century. But let’s not get into that argument. At least not right now . . .)

Second, we’re short of electric power. The power that goes to heat the water is also in very short supply. Load shedding (ie, blackouts!) is becoming more and more common as supply authorities attempt to cut peak loads. Those same powers-that-be keep telling us that if we don’t reduce our consumption of power, it’s going to get worse. (Those same powers [read politicians] that keep blaming us wasteful consumers, etc etc etc . . .)

Putting aside all the scare-mongering that’s going on in political circles (my spell checker wanted to change that to circuses, which would be perhaps more apt) it really does make sense for us, as consumers, to try to save both water and power – if only because that means less of our hard-earned dollars will end up in Government coffers.

One way to do both, of course, is to take shorter showers. How short?

The 4-minute shower

Believe it or not, it is entirely possible to take a shower in four minutes – including, if you need to, washing your hair. In fact, without shampooing, a sub-three-minute shower is perfectly practical. People in the bush who don’t have the luxury of hot water have been "getting" that sort of shower for years: get in, get wet, get clean, get out!

Let’s face it – all you really need to do is get wet, soap up and rinse off. Get wet: 30 seconds. Soap up: 60 seconds. Rinse off: 60 seconds. That’s two and a half minutes. Add another 60 seconds to shampoo your hair and there’s your four minute shower – with 30 seconds left over for good measure.

OK, if you agree that four minutes is enough time, how do you go about convincing everyone in your family?

The ST4 Shower Timer

This rather ingenious (and patented) design is completely automatic, turning on about 20-30 seconds after it "hears" the first "sssshhh" of the shower – giving you enough time to adjust the water temperature – then beeping each minute up to the magic four minutes, at which time it sounds an alarm.

The alarm stops when you turn the shower off. But if you try to fool it by turning the shower off for a moment and then back on again, the alarm will start back up again. It resets after about a minute of no-shower-sound, ready for the next person to take their shower.

Part of the secret to this circuit is the use of the piezo buzzer: it is not only sounds the beep/alarm, as you would expect but it is also used as a "microphone" to pick up the splash sound.

There’s no on-off switch; it simply operates when it hears the shower turn on (listening for the distinctive splashing sounds of the water). There is an internal 3-position switch and preset pot which are adjusted to give the desired sensitivity – once set, you can forget it.

There are also pots to control clock frequency and tone of alarm – but these are set in the factory and should not need touching.

It’s operated by a 9V battery (alkaline preferred) which should last for at least 12 months. Current drain, when ready to operate but inactive, is comparable to that of a smoke detector – around 10-15mA.

The circuit, including the piezo, is housed on a single PC board which fits (along with the 9V battery) into a purpose-designed two-part case. When correctly assembled is quite waterproof. Mounted on the shower wall it allows shower sound to enter and beeps/alarm to escape without the circuit getting at all damp.

The case, as we said, is in two parts. These snap together to form a nice, tight seal around the PC board, with alignment of the two parts taken care of by pins and holes which mate. Each half of the case is fitted with a suction cap which allows the unit to mount to any smooth shower wall (or even a glass screen).

While the ST4 Shower Timer is available fully built and tested, we are more interested in it as a kit which you assemble yourself. Even here, most of the hard work – soldering the surface-mount components and ICs – is already done for you. In fact, as supplied, the PC board is built and tested, ready for you to put together

Putting it together

Assembly is as simple as removing the backing and the centre from the self-adhesive "donut" foam ring and sticking it, as central as possible, onto the piezo transducer. Then similarly stick the rectangular foam pad onto the back of the PC board (it keeps the battery snug while preventing it shorting to or across the board), then push the PC board into the bottom half of the case.

 4-Minute Shower Timer Circuit Diagram

The bottom half can be identified by the slots for the transducer. When the board is pushed fully home, the foam donut "gasket" provides a seal in a moulded housing inside the case, preventing any water entering the case – theoretically even if dunked.

We say theoretically because it is designed that way – but commonsense would suggest you don’t try to prove it. Because the transducer slots are at the bottom of the case, spray would have to be travelling upwards to enter – possible, of course.

But the foam donut stops this water going any further. While the transducer itself is not sealed, its internal construction means that it is also an effective water barrier, so with the sealing donut in place, spray cannot enter the case nor either around or through the transducer.

All this means that the shower timer is for all intents and purposes waterproof, especially from spray. Once the PC board has been pushed home, the battery can be connected and slid down into the case, alongside the (now insulated) back of the PC board. It should be a relatively snug fit.

In the unlikely event that the suction caps have come off the case halves in transit, simply slide them back into their respective slots on each end – the photos show where they go. Slide the two halves of the case together, ensuring that the channels which hold the suction caps line up exactly – the pins in one half won’t mate if they don’t. The two case halves should "snap" together and that completes construction.

Testing

If you don’t want to get wet, you can use a small unmuted FM radio, off-station, to simulate the sound of a shower. (If your FM radio mutes automatically, or the mute cannot be turned off, this option won’t work. You’ll need to check it in situ – in the shower!) The FM radio will produce predominantly white noise, which is fairly close to the sound of a shower stream striking the bottom of the shower or bath.

Turn the radio on and the timer should give a chirping sound after 20-30 seconds (that’s the water temperature adjustment period). Then it should beep after each minute from there, with a series of beeps (7.5 seconds on, 7.5 seconds off) at the end of four minutes. Turn the radio off and the timer should reset.

Mounting in the shower

The timer always mounts vertically, with the piezo transducer towards the bottom. The suction caps should stick very well to any ceramic tile, glass or other smooth surface – if necessary, give ’em a lick first! Best position for the timer is about 300-400mm from the floor but it should work reasonably well up to about waist height.

If you need to mount the unit higher than this, or if it doesn’t appear to be sensitive enough, open it up and slide the switch up one notch. Don’t mount any higher than necessary. In some very low volume showers, (eg some gravity feeds), you might need to adjust the sensitivity right up but this would normally be unlikely.

You should not need to adjust any of the pots – they are preset on factory assembly. Once mounted, give it another run, this time with the shower. It should perform in the same way as it did in your "white noise" test.

The only time you should need to remove the unit from the wall is to replace the battery and this could be up to a couple of years or so! Don’t pull on the timer to remove it, slide a knife or some other thin, flat object under the suction caps to break the seal.