Washing machines?! Surely not!

Yes, if you have bought a new washing machine in the last few years it will probably have a digital display and pushbuttons. But isn’t that just for the sake of cosmetics? Isn’t the control system inside as it always has been?

The answer is a definite ‘no’.

The old way

In the good ol’ days, the "brain" of every automatic washing machine was its timer – an electro-mechanical device powered by a tiny electric motor.

The timer motor turned a series of gears that in turn moved cams to activate switches. The switches controlled the various functions – wash, spin and rinse, and so on.

In this photo taken from directly underneath the washbowl, the induction motor is at the top, driving the gearbox through a reduction belt drive. The brake motor is at bottom right.

While there was some control over the length of each stage, generally the sequence and duration of each event was fixed.

A pressure switch sensed the level of water within the bowl. A very sensitive device with a large diaphragm, the pressure switch connected to a chamber whose air pressure changed as the washbowl filled. The ‘water level’ control simply placed a variable mechanical preload on the switch.

The temperature dial was also mechanical in action, controlling the position of a water mixing valve.

Other controls included a power on/off switch, lid switch (preventing operation of the machine with the lid up) and an out-of-balance switch that stopped a spin cycle if the washbowl began to rock too badly.

Mechanically, the washing machine consisted of a stainless or vitreous enamel coated steel perforated drum, an agitator (a finned device rising from the floor of the drum), an electric motor (either a universal or brushless induction design) and a gearbox.

The main function of the latter was to convert the rotary motion of the motor shaft into the back-and-forth motion of the agitator. It also allowed the washbowl to spin at high speed, to remove excess water from the clothes.

So that was then – how about now?