If you are both an all-terrain biker and handy with a soldering iron, then we suggest you build this musical horn which, apart from the fact of having a much pleasanter sound than a simple bell, will usually make passersby turn to you with a broad smile, so surprised will they be to hear these few notes coming from an ATB or mountain-bike.
To achieve this, we have repurposed the SAE800 integrated circuit, which is theoretically designed for doorbells or musical chimes for houses. It takes only a very few external components and can run off any voltage between 2.8 and 18 V. So even with a seriously flat battery, it will go on working — though admittedly at the expense of sound volume. This is relatively high and can be adjusted, to a certain extent by potentiometer P1. Switch S1 is only vital if you want to make the battery last as long as possible. When the circuit is not activated, i.e. when push-button S2 is not pressed, it goes automatically into a standby-by mode, when it consumes only a measly 1 µA or so.
IC1 produces three different sounds, depending on whether E1 or E2, or both together, are activated. This is what we’ve decided to do here using diodes D1 and D2, as this lets us obtain the most attractive sound, consisting of three notes at 440 Hz, 550 Hz, and 660 Hz, partly overlapping and of decreasing amplitude for around 7 s. Of course, there’s nothing to prevent you choosing a different option by fitting only D1 or D2 and leaving the unused input floating.
The project doesn’t present any specific difficulties, but it will need to be fitted into a watertight plastic case, to protect it from the rain. For the same reason, it would be wise to choose a loudspeaker with a Mylar (plastic) cone, because the traditional fiber cone doesn’t get on very well with humidity. Switch S1, if used, and push-button S2 will also need to be chosen to be relatively resistant to humidity. The types available with a small rubber ‘boot’ are ideal.
Caution. The installation and use of this circuit may be subject to legal restrictions in your country, state or area.