Recently, the author had the need to create an MP3 player for a 93-year-old individual who had recently moved to a nursing home. Radio reception there was impractical due to interference from TL lamps. The elderly person in question had poor eyesight and limited dexterity due to arthritis, making it challenging to learn new procedures. To address the radio reception issues, a solution was devised: Integrating an iRiver U10 MP3 player into a speaker box designed to resemble an old-fashioned radio. The box features only an ON/OFF button and volume control. It operates on regular mains power and can function for approximately ten hours without being plugged in.
Unexpected Behavior Due to Firmware Issue
Surprisingly, the player exhibits an unusual behavior even when plugged back into the mains power supply. This oddity is a consequence of a firmware glitch in U10. When the USB connector detects a 5-volt signal. It erroneously assumes it’s connected to a computer, leading to an interruption in playback. The circuit diagram is straightforward and self-explanatory. The U10 is securely mounted in a rear window of the player with the keys locked, ensuring continuous playback regardless of whether the amplifier is powered on or off. (The author employed a 15-pound speaker set/amplifier designed for computers, which operates on 12 volts AC.)
Addressing Grounding Issues with Transformer Replacement
To circumvent potential grounding problems between the USB charging device and the amplifier ground. A double secondary winding transformer was used as a replacement. This modification has proven effective, ensuring seamless operation. The system functions flawlessly, providing the client with their favorite music for approximately 4-3/4 hours, akin to a personalized radio station experience. It’s worth noting that the player has the capacity to store significantly more music, especially since stereo sound is unnecessary, and the audio could be encoded at a slower rate.
Optimizing Output Level Matching
An initial challenge arose when the output level of the MP3 player didn’t align well with the amplifier’s input. This issue was resolved by selecting a different amplifier (Velleman K4001) with a more appropriate input sensitivity of 40mV. This adjustment ensures a seamless connection between the MP3 player and the amplifier, enhancing the overall functionality of the system.