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INTRODUCTION TO THE SM3
The Ramsey SM3 will duplicate the sound of a police siren at a low (200 mw) or high (2 watts) volume
depending upon construction. Closing a pushbutton switch will cause the siren to "wail" up in frequency
and opening the button will cause it to "coast" down in frequency. You'll find plenty of uses for the SM3.
Kids love to play fire truck or ambulance on their bikes and wagons (Mom will appreciate the low volume
setting here!) and there are the obvious uses for alarms and alerting.
PARTS LIST FOR THE SM3
1 .01 or .02 uf disc capacitor [if .01: marked .01, 103, or 10 nF if .02: marked .02, 203, or
20 nF], (C1)
1 47 uF electrolytic capacitor, (C2)
2 47K resistor [yellow-violet-orange] (R1, R2)
1 1.5K resistor [brown-green-red] (R3)
1 PNP power transistor [green] (Q1)
1 NPN transistor [small black] (Q2)
1 SM3 PC board
SM3—2
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