Hardware to play loud MP3 in traffic?

[Winfried]

Hello

I don't know much about electronics, but I'd like to build an MP3 player for use on my bicycle and play a loud car horn in case of emergency.

I thought about using car horns, but they draw a lot of current so require a beefy battery as well.

Before I investigate further, I'd like some feedback from experienced users about how feasible it'd be.

I guess I just need this:

• Compact MP3 player
• Waterproof loudspeaker
• Battery (li-po, li-fe-po?)
• Switch
• Cables

Thanks for any help.

 

[Gryd3]

Hello

I don't know much about electronics, but I'd like to build an MP3 player for use on my bicycle and play a loud car horn in case of emergency.

I thought about using car horns, but they draw a lot of current so require a beefy battery as well.

Before I investigate further, I'd like some feedback from experienced users about how feasible it'd be.

I guess I just need this:

• Compact MP3 player
• Waterproof loudspeaker
• Battery (li-po, li-fe-po?)
• Switch
• Cables

Thanks for any help.

Many Lithium batteries use in RC cars/planes/helicopters can pack quite a punch and provide a lot of current. The question here will be if you plan to charge it every night, or if you plan to put a dyno on your bike.

 

[Winfried]

I probably won't need to charge it that often, since it's only to be used instead of a loud car horn and only in case of emergency.

I was more worried about how 1) big the speaker has to be and 2) much energy the amp will use.

 

[Gryd3]

I probably won't need to charge it that often, since it's only to be used instead of a loud car horn and only in case of emergency.

I was more worried about how 1) big the speaker has to be and 2) much energy the amp will use.

Unfortunately, I am not enough of an audio guy to quote you a decent size speaker or amp. Anything I provide in that regard would be a guess, but I'd guess you should aim at the 20Watt mark for an amp and use a couple 4" speakers, or a 4x6" car speaker.

The amp will be variable, but a 20W amp will draw up to 2Amps from a 12V battery.

 

[Winfried]

Thanks much for the feedback. 2A isn't bad but thankfully, I won't need to use it often so I guess a small li-fe-po battery could do to power the amp + two speakers.

 

[Gryd3]

Thanks much for the feedback. 2A isn't bad but thankfully, I won't need to use it often so I guess a small li-fe-po battery could do to power the amp + two speakers.

I just want to confirm that theses speakers are for music, and you will be using an alternative for a 'horn'?
Those may not be loud enough to be heard from within car unless you are pretty close and they don't have excessive external noise dampening. I still think a horn or siren is desired for emergency use.

 

[Winfried]

The speakers will only be used to play the horn. I don't listen to music while I ride.

Hand horns work OK, but in an emergency, it's just not as safe as just pushing a button:

 

[Gryd3]

I thought you were trying to do both. MP3 music normally, and a horn for emergencies.
I'd use a motorcycle horn and a couple RC Lithium batteries then.
Some RC cars draw more amperage through the motors than 5 Amps. All you'd need is the horn, batteries, a relay and button. (Optional resistor)

 

[Winfried]

I thought the MP3 + amp + speaker solution would use less power and be lighter, but car horns + battery is fine. Thanks for the info.

 

[Gryd3]

I thought the MP3 + amp + speaker solution would use less power and be lighter, but car horns + battery is fine. Thanks for the info.

You're right, but if you want the volume, you'll need to draw more power. You also won't get a louder horn with audio equipment unless you specifically build it to produce a horn sound.

The motorbike horn draws less current, and the circuit will draw nothing unless you push the button. Just make sure the battery has at least a peak discharge of 5A and you're golden. You just wont be able to lay on the horn all day or use it for weddings

(Less components, and easier wiring)

 

[KrisBlueNZ]

I agree with Gryd3 here. An audio amplifier and speaker are not the answer. Speakers are designed to reproduce a (reasonably) wide range of frequencies fairly accurately, and are not very efficient (modern speakers are 5% or less, usually). A horn will be a lot more efficient in terms of power consumption, but especially in terms of size, because it uses a resonant chamber (at least, car horns do) and a tapered vent.

You'll probably end up using a battery powered electric horn. The battery doesn't need to have a lot of capacity but it needs a high short-term current capability. Lead-acid would be good, apart from the weight. Lithium ion might be best.

If you just want to make a lot of noise, a motorbike horn may be best. If you want to sound like a car, get a car horn! You may be able to adjust it internally to reduce the power consumption at the expense of a slight reduction in volume.

 

[Winfried]

Thanks for the infos.

I actually already got those 12V car horns that come with a 30A relay.

As for the battery, I read that lead-acid can be a bit heavy for use on a bicycle, so should look at li-po or li-fe-po instead with a high C (discharge rate in Coulomb?).

 

[KrisBlueNZ]

Yes. According to the battery type comparison at http://en.wikipedia.org/wiki/Comparison_of_battery_types the highest energy per weight is Lithium Polymer.

 

[Winfried]

So li-po or li-fe-po it is. Apparently, li-fe-po batteries are less prone to explosion in an accident so should be a safer choice for use on a bicycle.