One of the things I don’t like about the Olimex MOD-MP3 player is it’s need for 3.3V. It’s not a standard “homebrew” value (we like playing with 5V or 9V). While they do have a 1.5 AA battery and booster on the board, it seems to chew through that battery pretty quickly.

So, I knew I had to build a 3.3V power supply. Luckily, National makes a great supply chip, called the LM2937ET-3.3. It’s much like their other regulator chips: Give it juice, and it spits out nice clean regulated voltage.

Since I already built out a 12V supply for the radio (to drive the Audio Amp, and CMOS logic), I figured I’d dump 12V into the LM2937 and let it handle the rest. It’s a newer chip, so it’s better at handling those drops without dumping too much to heat. (The input voltage is rated up to 26. Quite a range.)

So, now I have a 12V supply and a 3.3V supply and the Olimex runs great on the external supply. No more batteries. Here’s a shot of the supplies:

At the left you see the (dinky) transformer from the original radio (it was AC powered). I kept it “just in case” and I’m glad I did. It gives enough power (about 18V) to drive the LM7812, which gives me clean 12V. The middle board is the 12V board. Look at that giant cap and heat sink. I’m a big believer in making power supplies robust. If they blow, all kinds of damage could be done (including risk to life).

At the far right you see the new 3.3V supply using the LM2937-3.3. The output should dump to a 10uF (or greater) capacitor, to give the design some additional stability. I went with a chubby 100uF I had on hand. Super overkill, as that bugger is rated at 200V. No risk of burning it out!

In general, you want to have big, high-voltage rated, caps in your power supplies. They help “even out” blips in the power and help provide rock-solid clean power for your downstream components. They also help with handling inductive loads (like motors). No big loads here, but better safe than sorry when it comes to a power supply.

The bottom board is the Olimex MOD-MP3 player board, sans AA battery.

Next up, I gotta get that rotary encoder circuit working. That’s the only major part left before I can put together all the pieces.