# Low power way to make a sound

I'm designing a 3V button cell battery powered device. I want it to beep or click or just make any noise at some times just loud enought to be heard across the room.

I've made a prototype working on 12v - it's just an opamp comparator that goes high and low and i've connected a piezo speaker to output of opamp with a cap in series. It makes clicks when opamp goes high or low and they are just loud enough, but when i lower voltage to 3v, i can barely hear the speaker.

Can anyone suggest me a solution?

This piezo buzzer is rated for 3 V operation and produces 100 dBA at 10 cm, which is 80 dBA at 1 m, and 60 dBA at 10 m.

Maximum current is 9 mA, so if you would give one 100 ms burst every 10 seconds your battery will last 4 months.

• yeah, but i've red in wikipedia, that CR2032 batteries can deliver 3mA max. anyway, i'll try with low voltage piezo, as the one i have is from unknown junk bin – miceuz Jun 18 '12 at 16:14
• @miceuz - Since you'll probably need only short bursts you can buffer the 3V with a capacitor. A 1000 $\mu$F capacitor will be sufficient for 100 ms bursts. – stevenvh Jun 18 '12 at 16:16

Some buzzers work with a DC voltage and some need an alternating voltage.
It sounds like you may need to drive your piezo buzzer with an alternating voltage, not a steady one if you want a continuous tone (if you want a click stick with the type you have). The datasheet should tell you this.
They also come in various voltage ratings, so you should be able to find one that works at 3V.

This buzzer will work at 3V and needs a alternating voltage (see datasheet) This will "click" when the comparator output changes.

In comparison, this buzzer will work with a DC voltage, as it mentions a "built in oscillating circuit" and operating voltage of 1-20V DC. This will produce a tone when the comparator output is high.