Just recently the author had cause to make an MP3 player for a 93-year old recently moved to a nursing home. There, radio reception turned out to be hopeless, mainly owing to interference from TL lamps. The elderly person involved can neither see well nor has good manipulative skills (arthritis), while learning new procedures is sure to present problems. The solution to the radio reception problems was to build an iRiver U10 MP3 player into a speaker box which looks like an old fashioned radio and has only an ON/OFF button and volume control. The unit is powered by the normal mains and can remain unplugged for about ten hours before it stops.
Remarkably, that also happens on being replugged into the mains. Due to a firmware problem of the U10, on 5 volts appearing on the USB connector it assumes it is connected to a computer and stops playing. The circuit diagram is all straightforward and speaks for itself. The U10 is fixed in a window on the back of the player with the keys locked. Hence, it plays continu-ously whether the amplifier is on or not (the author used a 15-pound speaker set / amplifier for a computer which switches the 12 volts AC).
The transformer was replaced with a double secondary winding to avoid any earthing problems between the USB charging device and the amplifier ground. The unit is working well and plays the client’s favourite music for about 4-3/4 hours, more or less like a personal radio station. Of course, much more music could be loaded on the player since stereo makes no sense and it could be encoded at a slower rate. An initial problem of the MP3 player’s output level not being well matched to the amp input was solved by choosing another amplifier (Velleman K4001) which has a more suitable input sensitivity of 40mV.