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A Smart Mixture Display For Your Car

A 10-LED display indicates the fuel mixture, while a small buzzer sounds if the mixtures go dangerously lean.

By Julian Edgar & John Clarke

THE SILICON CHIP Mixture Meter – first presented in 1995 – is one of the most popular performance car electronic kits ever produced. Literally thousands have been built, each showing by means of 10 coloured LEDs whether the air/fuel ratio is rich or lean.

While such a design – which works from the car’s standard oxygen sensor – won’t give you an absolutely accurate readout of the mixture strength, it’s far better than having no indication at all as to whether the car is running rich, lean or at stoichiometric (the latter means an air/fuel ratio of 14.7:1). As a bonus, it also clearly shows if the car is in closed or open loop mode

The new Smart Mixture Display presented here still displays the mixture strength by means of 10 LEDs – red for lean (red is for danger!), green for mid-range mixtures and yellow for rich. However, we’ve added three important extra features with this new design:

(1). Better protection of the electronics (in some cars, the old design was prone to blowing its chip);

(2). An automatic dimming function for night driving; and

(3). An audible lean-out alarm.

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