Vintage XM Radio
This Project was submitted to Parallax by David Donovan.
Vintage radios have a charm and character that begs to be restored to working condition. Occasionally, too many years of hard use make chassis restoration almost impossible. The radio in this article had a nice cabinet to work with but the electronics looked as if they had gone down with the Titanic. Corrosion, rust, broken and missing parts made the thought of working on the chassis a nightmare. However, a satellite tuner and a stamp processor allowed this radio to work again in a slightly different way than originally designed over 70 years ago.
The concept: replace the original AM radio with an XM radio. A primary goal was to maintain as much of the original look of the radio as possible, and to have all modifications be reversible, so the radio could return to its original condition if desired.
To build the project, the original chassis and components were replaced with the following:
- XM tuner
- BS2P Stamp processor
- Optical Encoder
- Vacuum florescent display
- Preamp/Amplifier
- Speakers
- Power supply
 The key to this conversion was to find a way to control the XM tuner using controls on the vintage cabinet. In order to accomplish this I needed a way to 'talk' to the tuner. Finding an XM tuner which provided a serial interface for control made this possible. There are a few options to choose from that provide such an interface via RS232. The tuner I selected had such a port and the command set was easy to understand and program. An optical encoder was used to select stations and song information from the tuner was sent to an external display.
The BS2P stamp counts clicks from the encoder updating the display with a pointer changing its position and also a digital readout of the 170+ station numbers. The pushbutton on the encoder selects the station. When the encoder is pressed, the stamp sends the appropriate control to the tuner on the serial interface and then updates the display with the artist/title information. To keep the information current on the display, the stamp checks the artist/title information every 10 seconds and updates if there is any change. To check if the encoder has moved, the stamp code simply loops looking for any state change. Six pins on the stamp were used for all I/O (2 for encoder output, 1 for encoder pushbutton, 1 for tuner input, 1 for tuner output, 1 for display).
The display used for the project provided a serial interface and a basic instruction set to program it. It allows redefinition of characters, and this feature was used to create a character that looked like dial pointer. The display chosen was a vacuum tube florescent display (vfd) that provided a characteristic vintage look and fit nicely in the opening where the original dial had been located.
The preamp and amp for the XM radio were made using a kit compatible with the supply voltages needed for the stamp. No interface was necessary between the stamp and the preamp/amp except sharing the common 12V power supply.
The original mono speaker was replaced with in-the-wall speakers which provided a somewhat unnecessary left and right channel. The in-the-wall speakers were easy to work with in the existing cabinet. Mounting them did not require any significant modifications to the cabinet.
To provide power for the display at 5 volts and the stamp/preamp/amp at 12 volts, a dual source linear 5V/12V supply was used with conservative power ratings. The vintage XM radio project turned out nicely. It was a very good project to learn the basics of stamp programming and circuitry. I would recommend such a project to get your feet wet. It is very approachable and can easily be split into subtasks to confirm success throughout the project.
 If you have any questions or comments, about this project please feel free to contact me. Both XM and Sirius have radio models that support a serial interface to provide I/O to a stamp. I would happily supply a parts list and suppliers if requested. Here is a basic block diagram of the circuit for the tuner/display/encoder and the code.
Save those old sets! Bring them back to life with a little care. If the original circuit is too far gone, consider modifying to a satellite radio. Using a stamp processor, you can easily update the radio with software changes and modifications to provide many more years of joy.
Photos and specifications of the Vintage XM radio are courtesy of David Donovan.
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