If you’ve ever been out in the country where a field of sunflowers is blooming, you’ve probably marvelled at the way they all turn to face the Sun as it tracks across the sky. Thousands, perhaps millions of flowers, all facing the same direction.

Naturally, they do this to extract the maximum amount of energy from the Sun; energy converted by the plant’s chloroplast.

In our electronic version, two solar cells do a similar job, "catching" the energy from the Sun and converting it into electricity. The electricity is stored in a capacitor and used to turn a small electric motor.

The motor is controlled by a comparator circuit which gets its information from a pair of infrared diodes. If the energy being received (from the Sun) by both diodes is equal, it’s a reasonable bet that they are both aimed towards the Sun. But if one diode receives more energy than its mate, it’s just as reasonable to assume that it has a better aim than its mate – so the comparator turns the motor on to adjust the direction.

It does this in "fits and starts" – it’s certainly not a smooth motion but is quite jerky. In most control circuitry we’d call this "hunting" and steps would be taken to eliminate it. But in the Sunflower, it actually is quite natural. If you’ve ever seen stop-action photography of a sunflower, it does move in fits and starts!