Portable Active Speaker

A portable audio amplifier; connects to a walkman, musical apple pod, or anything else with a headphone socket. It was built mostly from bits I had lying around. The speakers (3" woofer and a 1" tweeter - magneticaly sheilded too) came out of what's left of an old Akai television (I would fix it, then a few months later it would break again so decided it's more useful as parts). I'm not really sure of the power rating but I guess it's about 7 watts. The speaker grill was made from a rusty gauze mat, painted black and bent into shape. And the whole thing is housed in Jaycar's biggest jiffy box.

The amplfier is based on the TDA1510AQ (there's nothing special about it - I just had a couple of 'em in my bag of amp ICs)  amplifier IC connected in bridge configuration (I just built the application circuit). It provides plenty of output power, enough to overpower the speaker at high volume.

For a power source I used a small (by compairson) 12V 1.3Ah sealed lead acid battery. When fully charged it can run the thing for about five hours. SLA batteried don't like being left in a completely discharged state so I built in a little battery monitor circuit (board mounted on the top-left side on the above pic) to warn the user when the battery starts to get too flat. This circuit measures the battery voltage, when it drops below a certain threshold (equivilant to about 20-30% battery capacity remaining) the power light starts to blink. To charge the battery an AC adaptor, anything from 17-23VDC,  is connected to the DC socket (next to the switch). This voltage goes to the battery charger/external power board (top-right, hiding behind the amp board) where it's regulated and fed to the battery (trickle charge).

... 4/12/05