AT121, AT-121 to AT150 converter

Two-Tone Train Horn
$19.95

With this circuit you can electronically simulate the noise of a diesel-train horn. The sound is triggered automatically as the train reaches a desired place on the track so you can produce the sound as the train approaches stations, level crossings, etc.
The circuit can be built simply by using one 556 or two 555 timers. The rest of the parts are readily available and not critical. The output power from the two-Tone train horn is adequate to drive a miniature loudspeaker directly so all that is required is a single 9V alkaline battery or a 9VDC wall-adaptor.

[Click here for the full article.]