Hardware Hacking - Nicolas Collins

Hardware Hacking 109

Figure 2 Figure 3

This circuit puts out about 1/4 watt of audio power, and can be used to drive
small speakers or headphones. It runs nicely off a 9 volt battery or a set of 4 AA
batteries. Via the backwards transformer arrangement shown in Chapter 8 it can
also drive a Piezo disk at very high sound levels. This amplifier can drive a
small motor (such as the vibrating motors from cell phones and pagers, also
discussed in Chapter 8) or a low-power solenoid, instead of a speaker, to make a
driver that, with a more extended low frequency range, is a kind of subwoofer
complement to the Piezo.

There are numerous similar amplifier chips on the market, some capable of
putting out many Watts of power, but most require a substantial “plug into the
wall” power supply. The LM386 is a good “starter amp.”