Thomas Radio Mod

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Overview

This is a personal project. Planning on modding up an old Thomas radio. Well, it's not really an true Thomas radio. But one that was made to look like it. It's still fairly old (made in 1988) but not nearly as old as a real one. Which is good because I don't feel bad modding it up and is why it only cost me $20 ;)

Thomas Radio

It has a very nice look to the radio. It has a working AM/FM tuner that actually moves the big dial you see. A small light adds a yellowish glow as well. There is a cassette player installed on the side of it. My plan is to remove the cassette player and mod in a MP3 player instead :D

Inside of Thomas Radio

Here you can see there is just one 2W speaker and a separate Cassette system on the bottom left. My goal is to remove the cassette and substitute an MP3 player. I selected the RCA MP3 player from walwart for like $30.

RCA MP3 Player

You can read the feature list. It's actually hard to find a cheap MP3 player that doesn't have video screens these days. I took it apart to see what all I have to work with.

Inside of RCA MP3 Player

Sorry the picture is grainy. But basically we have a little screen, 4 buttons on the front like a compass (N = Volume Up, E = >>, S = Volume Down, W = <<). Two on top, power and play. There is also a small 1.5V battery on the back and a MIC. You can see a USB cable for uploading of music as well.

Remove Cassette Player

I need to remove the cassette player and figure out what lines lead to the cassette and what they do. I maybe able to just tap into those.

Cassette Wires Measuring Volts

I was thinking the orange cable was the power + because of the read cable going to the power but instead it was the yellow cable. There is basically a switch that triggers when a cassette is inserted. Then the orange/red cable becomes live. Interesting that it feeds power back into the device...

Other issue is we have basically 12 volts coming in and we only want 1.5V. So I think I will try to use a LM317 Voltage Regulator and 220-ohm and 47 ohm resistors to step the power down. (Got them from Radio Shack)

Convert Battery to use Radio's Power

I manage to get all the parts I needed over at Radio Shack (w00t!) So I used the LM317T, R1 was 220-ohm and R2 as 47-Ohm, This gives me a 1.526V output. I also bought a bread board because I'm a total n00b at this. I spaced out my parts just to keep everything in order. I used this calculator/schematic http://www.electronics-lab.com/articles/LM317/

Circuit board layout It's Alive!!

We wired it to the MP3 player just to test it out and it works! I need to disable the push button on the board (it had an on-off switch) This way it just comes on with the radio is turned on.

Get MP3 player working with Radio

Ok, I decided to use all the wires from the existing cassette player. With a bit of playing here is the existing wire layout.

  • Yellow Wire: Main power from system (12V)
  • Black Wire (thin): Ground
  • Black Wire (thick): Speaker wire
  • Green Wire: When given 12V then the Radio is "on"
  • Orange Wire: When given 12V then the cassetteMP3 player is "on"

Once that was learned it is now possible to make a switch to toggle between powering the radio and powering the MP3 player. Most stuff on the MP3 player is surface mounted and not fun to work with. For audio I bought a $1 pair of headphones from Big Lots and cut off the speakers. Then I twisted the left and right wires together and attached them to the think black wire. This provides the MP3 audio output, w00t!

Build Harness

Ok, measuring out the gap from the cassette, and looking at my spare parts to decide how I'm going to make a faceplate for this. I have a sheet of 12"x12" brass plus these parts:

Extra salvaged parts

Make Buttons and External Interface