Radio Shack has a module called a "20-second Recording Module". I became aware of this module through the various Yahoo Groups mailing lists. The module comes complete with everything except a 9V battery. The battery will become unnecessary once you hook the unit up more permanently to the layout. The whole unit is already assembled, so you just need to record and play the recording back. The possible applications are enormous (road crossing bell, factory sounds, traffic noise, background birds, locomotive sounds, etc.).
My first project is to see if I can tie the playback trigger to a stationary decoder output. That way it can be triggered from the throttle. The diagram shows my design for how to connect the DS44 (Digitrax stationary decoder) and the recording module. The basic idea is to have the ON/OFF trigger of the DS44 control whether or not the recording module is playing back its recording. If the DS44's output is set to "C" (close), the module should be playing, if it is set to "T" (throw) it should be off.
The communication is done through a relay so as to account for the voltage differences. We want a "normally open" relay so that by default the sound is off. Of course, once the system is connected to the DS44's output, the DS44 will be in charge of the initial and current position. Next, I decided on a relay that is designed for a 5V coil. The DS44 puts out about 10V. The resistor R1 is used to drop this voltage down to the relay's 5V. I decided on a Radio Shack relay (see link on the above-right). R1 will be set to 220 ohm. Well, I went off to the workbench and built the design shown above. To my surprise it actually worked right away - sort of... It turns out that every time I press the button on the throttle, the playback of the recording module is triggered. It doesn't act as an on/off system, but rather as a trigger system. By the way, I soldered the black wire to the negative lead of capacitor C1 on the recording module and the positive lead (red) to the end of resistor R1. Although the project didn't turn out exactly as I had envisioned, I am still happy with the result. Triggering the circuit is easy now with the throttle. I need to work on the recording quality and content.
I decided to experiment with ways to improve the sound. From the various mailing lists and web sites I learned that PVC tubing would help. After experimenting, the PVC tubing I am using is flagged as "1-inch". The RS speaker measures 1.5 inches in diameter. I have never understood the "logic" that plumbers use, but there is nothing on these tubes that resembles "1 inch" (the I.D. is just under 1.5" and the O.D. is a quarter of an inch bigger). Oh well...
Using Liquid Nails for Projects, I glued the rounded cap tube to the back of the speaker after carefully sanding some of tubing away to clear the wires of the speaker. I used the metal polishing disc on the Dremel tool.
Here is a photo of the final assembly. There is a two-inch straight tube glued on top of the speaker itself. This helps tremendously in the recording as well as the play back volume. The tubes do color the sound quite a bit, as any cheap stereo speaker does, but it will be good enough for background noise.