Step 4: HOW TO BUILD AN IPOD CHARGER
1 push on/push off switch - Radio Shack - 275-617 $2.49
1 5V Fixed 7805 Regulator - Radio Shack - 276-1770 $1.59
1 10uf Capacitor - Radio Shack - 272-1025 $0.99
1 100uf Capacitor - Radio Shack - 272-1028 $1.29
1 Diode - Radio Shack - 276-1104 $0.89
2 50K ohm resistors - Mouser Mouser Industries - 270-49.9K-RC $0.11
2 75K ohm resistors - Mouser - 270-75K-RC $0.11
heat shrink tubing
The first question is where to get the 5 volts. I decided to look at the circuit that drove the cassette tape motor. After ripping out the cassette tape mechanism, I fiddled with it trying to determine how it worked. Boy it looks complex!
The mechanism has many levers and springs but it is fairly simple. The play lever pushes down the tape head carriage and a reed switch that activates the audio and motor circuit.
Like Instructable Sony boombox I wanted the ability to turn on/off the iPod charging circuit. So I bought a Push On/Push Off switch at Radio Shack. It's the red button in the photos. I measured 10 volts on the motor circuit and confirmed that it turned off when the Stop cassette button was pushed (which disengaged the reed switch). Sure, there are many 5 volt circuits on the main board but those circuits did not sync on and off with the cassette tape audio circuit. Plus, the circuit connection was easy, since both the reed switch and the motor circuit were both routed through a single connector on the main board.
The next challenge was to convert the measured 10 volt to 5 volts. I started with this Instructable. Super Simple I searched the internet further and found this circuit and decided to use it. 5 Volt Regulator Build
Another trip to Radio Shack, a scrap of old perfboard, some soldering and blam, a regulated 5 volt source that could be used to recharge the iPod.
I used the connector that powered the motor and reed switch. I wired the output to the iPod docking connector (pins 16 and 23) Pinout.
I modified the cassette mechanism mounting bracket to hold the new 5 volt regulated charging circuit.
In STEP 3 I mentioned the "do-over". Well at that time, I found the iPod wasn't charging! It was getting the 5 volts but the iPod charging bolt would come on then disappear. That meant the iPod was running on battery while docked! Doh! Back to the internet for more research, I went. I found that newer iPod firmware requires a small voltage on pins 25 and 27 in order to charge. Why oh why!? Like I said, I wanted to drop kick the thing. Persistence yields perfection.
Hint - There is more than one way to charge an iPod. In STEP 2 I mentioned I bought two iPod chargers. I pulled out a VOM to analyze these chargers since I knew both of them actually charged my iPod. I found something interesting. One charger used an AA battery as a power source. The other used a wall wart. Both had different charging circuits. The battery powered charger used the typical 5 volt USB type power (pins 16 and 23). The wall wart version used the 12 volt Firewire circuit (pins 19/20 and 29/30). The Firewire version was more attractive, since it didn't require any additional components. Simply connect 12 volts to pins 19 and 29. However, I didn't have a 12 volt source on the main board. The power supply circuit of the boombox had only an output rated at nominal 9 volts. So I took apart the USB style charger and found a bunch of resistors configured in a simple voltage divider circuit.
These resistor (50K ohm, 75K ohm) values aren't available at Radio Shack so I ordered them from Mouser...and waited anxiously for UPS. After getting the four resistors I created a small subBoard.
I soldered and glued this board to the main charging circuit board and wired it up.
I tested and found it didn't charge! I jiggled the docking connector and found I mounted the docking connector too low. The charging circuit pins were not making good contact with the iPod. Doh! I had to break the glue bonds on the cradle (again) and reinsert the connector into the cradle. Success! It was finally charging.
Lastly, solder and heat shrink the connections to the red Push On/Off button that was mounted in the docking cradle in STEP 3. You use the wires that were connected to the reed switch mentioned earlier. Remember, that reed switch activated the audio circuit and the motor circuit (which now acts as an iPod charging circuit).
You should now have a docking cradle that charges your iPod and plays music through the boombox! Booya!