Adding an auxiliary input to my portable radio
Like many people I love listening to podcasts, so when I was finally given permission to bring a small personal radio into a previous job I figured that instead of listening to the radio I'd use it to play podcasts from my iPod.
The radio I panned on using was the Sony ICFS22 Personal Radio, which had been gathering dust on a shelf for a while. The only problem though was that it didn't have an auxiliary input for my iPod to plug into, so instead of buying a new radio I decided to have a go at adding one myself.
Opening the radio
Tentatively opening the radio's plastic casing it became immediately obvious that the component of interest was the IC surrounded by passive components, which after closer inspection bared the markings "CXA1019S".
It didn't take long to find a datasheet for the CXA1019S that contained a diagram of the IC's pinout, however not being terribly experienced in electronics I was unable to determine what pair of pins would allow for a direct audio input.
So still with a confidence that the IC was the correct component to focus my attention on I decided to imprudently test all the IC's pins in the hope of finding the correct pair.
Finding the correct IC pins
Unable to determine which pins to feed the audio into from the datasheet I decided upon a process of elimination.
Starting by turning on both the radio and iPod I plugged a pair of earphones into the iPod and stripped off one of its "in ear" speakers; exposing the red and black wires. Then with the black wire placed against one of the IC's ground pins I began to sequentially touch the red wire against each of the other pins.
Half expecting the IC to die I was most surprised when after touching the wire against the 6th pin I heard some rather nice music from my iPod coming out of the radio's speaker.
So having discovered the correct pins I soldered a length of wire from the IC's ground and 6th pin to a 3.5mm stereo jack socket and secured it to a freshly drilled hole in the back of the radio (a random place for a socket I know).
To this day the radio amplifies the external audio quite nicely and what is even nicer, and something I hadn't considered, is that the radio signal is suppressed when the auxiliary input is in use.
Admittedly the process I went through to find the correct IC pins could have easily broken the IC but in my case the enjoyment I gained from opening the radio up and experimenting far exceeded any disappointment that could have resulted from braking it. I always find such follies into DIY electronics great fun, regardless of the outcome.