Here’s a project sure to head off your road rage. Instead of silently fuming the next time you’re stuck in traffic behind some attention-deficient driver who fails to move when the light turns green, just give him a friendly yet firm word of encouragement through your DIY megaphone. He’ll definitely get the message. The device projects your voice using a small microphone connected to a preamplifier and boosted with a power-amplifier circuit. It won’t deafen anyone, but it can provide a step up to more than twice your normal speaking volume. Of course, you don’t have to be on the road to use it—the megaphone comes in handy anywhere you find yourself needing to send a message loud and clear.
Make a Compact DIY Megaphone
Time: 5 Hours
- Mic Preamp Kit – (SparkFun Electronics #PRT-08872; $2.95) NOTE: this kit must be built from separately-purchased components; approx. $5.00 extra.
- LM1877 (Digi-Key #LM1877M-9-ND; $1.64)
- 3-100K resistors (Digi-Key #CF1/4100KJRCT-ND; $0.24)
- 2-1.8K resistors (Digi-Key #CF1/41.8KJRCT-ND; $0.24)
- 1M potentiometer (Digi-Key #3306F-105-ND; $0.71)
- .1mF ceramic capacitor (Digi-Key #399-4454-1-ND; $0.13)
- 2-4.7mF electrolytic capacitors (Digi-Key #493-1056-ND; $0.36)
- 220mF electrolytic capacitor (Digi-Key #565-3062-ND; $0.98)
- .47mF electrolytic capacitor (Digi-Key #P13474-ND; $0.11)
- 9V battery (RadioShack #23-1123; $5.49)
- 9V battery clip (RadioShack #270-0325; $1.99)
- 8-“AA” batteries (RadioShack #230-1127; $8.99)
- 8AA battery holder (RadioShack #270-0387; $1.99)
- 2-SPST momentary switches (Digi-Key #509PB-ND; $2.82)
- Project box (Digi-Key # SRH67-9VG-ND; $8.32)
- 8-ohm 2W speaker (Digi-Key #668-1191-ND; $4.81)
1. Download our schematic circuit diagram. Assemble the mic preamp kit [A] per the instructions on www.sparkfun.com/categories.php.
2. Build the power amplifier [B], which combines the output of the two two-watt channels that are inside the integrated circuit.
3. Connect the nine-volt-battery clip’s black lead to the mic preamp’s GND pin, and its red lead to one SPST switch [C]. Wire the second pole of the SPST switch to the on/off pin for the mic preamp kit. Pressing this switch will activate the microphone.
4. Wire the positive lead from the eight-AA-battery holder’s clip to the second SPST switch [D], and the negative lead to the amp’s GND pins. Attach a wire between the second pole of the switch and the 12-volt power-supply pin. Pressing this switch will fire up the amplifier.
5. Insert all the components into the project box, connect the speaker, and install fresh batteries. Press both switches simultaneously to activate the megaphone. Adjust the potentiometer for optimal voice quality and volume.