Power setup for musical birthday card

[dohzer]

I'm currently designing a little musical birthday card, and I've finished the SD Card/FAT/WAV code in my STM32. I still need to write the LED part of the code, but I've started thinking ahead to the hardware and power setup.

For the proof of concept I used a little TI headphone amp chip (since I had it at home) powered from the 3v3 micro controller rail. I could hear it but it definitely wasn't loud enough for a finished product. I'm assuming I'll need a higher voltage.

I haven't selected a battery yet, but I think I'll either use a 9v battery or a flatter setup with several AAA batteries. I like the AAA idea so I can tap at different points for the micro/LED rail and have the full voltage for the speaker. The other option would be a small battery with a step-up regulator for the speaker rail.

My main question is if anyone could recommend a power setup or regulators and also a simple amplifier circuit/chip for a small compact speaker? Are there any low voltage amplifiers that have internal boost regulators?

 

[Audioguru]

A musical greeting card does not use a low impedance speaker and does not use a high voltage battery.
It uses a high impedance piezo transducer to make low level squeaking sounds and is powered from a small coin cell battery.

If you want to make a compact sound system then use a battery of a few volts to power a bridged amplifier IC. The bridged amp effectively produces power almost 4 times more than an ordinary amp that drives a low impedance speaker.
Years ago there were many amplifier ICs available. The TDA2822M would have been perfect for your project. Today most are not made anymore.

 

[dohzer]

A musical greeting card does not use a low impedance speaker and does not use a high voltage battery.
It uses a high impedance piezo transducer to make low level squeaking sounds and is powered from a small coin cell battery.

I figured that was how they got the volume with such a small battery, but like you say, they only use "squeaks". It's not really feasible for proper music, is it? I'm wondering what kind of power I can pump through a small speaker like, say, one from a PC motherboard/case.

The TDA2822M would have been perfect for your project. Today most are not made anymore.

Thanks for that. Just the kind of info I'm after. I'll buy some (or similar... looks like end of production) and try them out.

 

[Audioguru]

A very cheap speaker on a pc motherboard will produce only mid frequencies with no bass and no treble. Beeps and bad sounding speech, not music.
There are some small speakers that sound very good. My son bought a cheap Chinese amplified speaker for his phone. It uses a 2" diameter long throw speaker in a small ported enclosure. It has a "3.7V" rechargeable Lithium battery and its amplifier is bridged with an output power of about 1.4W into 4 ohms at low distortion. It probably has some bass boost because its bass is amazing for its small size.