I've started to experiment with sound for AF trains. Here's my first attempt at replicating an Air Chime Whistle Generator with solid state components. The original ones used electro-mechanical vibrators to switch the track voltage between the voltage at the Variable output terminal and the 15 V accessory terminal. The circuit below just turns on and off the track voltage from the variablle output terminal at a frequency set by the variable resistor. As a result, this circuit, unlike the original Air Chime Whistle Generator, does not work without at least slightly turning on the track power. The optional resistor and diode will provide a capability to make a sound when the train is stoped, but it doesn't sound that great (Not that the Air Chime Whistle sounds very good in the first place). Note that one of the side effects of the original Air Chime Whistel Generator was that some engines could creep forward with the control knob turned off and the Air Chime Whistle Generator Activated. This won't happen with this emulation
I breadboarded the schematic linked below, but have not created a permanent circuit. Note that it is designed such that one could use the base for an Air Chime Whistle Generator and create a new "can" containing the circuit.
Air Chime Whistle Generator Emulator Schematic
Many years ago a friend gave me the shell of a NOMA Talking Station. I finally got around to building this project in May - June 2020 as part of a "Coronavirus Project"
My final solution is based on a Raspberry Pi microcontroller and a simple audio amplifier. The Raspberry Pi is a bit slow to boot, but otherwise my
solution is quite acceptable.
October 2020 update: Decided to use an external amplifier to make it louder ... modified to enable using an external amplifier via an RCA Jack.
The following packages were installed on the Raspberry PI
pigpio python-pigpio python3-pigpio
samba samba-common-bin // set up shares to make it easier to update the software and add sound files
telnetd // enables remotely logging into the Raspberry PI
1 Previous (go to previous sound file) (decrements one on each press when in Ready mode)
2 Next (go to next sound file) (add one on each press when in Ready mode)
3 Play (Play the current sound file) (plays current sound file - enters Playing mode -- returns to Ready mode when done)
NOMA station push button (Play current sound file then advance to next sound file)
reset button: executes a reboot or halt if pressed for more than 3 seconds
The index number, filename and 16 char description of the sound file is contained in a configuration file
Source Code for Raspberry PI