How I used a cheap recordable sound module as a loco sound card - Part 2

In Part 1, I described how I added a simple recordable sound module to my double-diesel loco to give it the basic sound effect of a diesel engine in action. However, there was no way of adding a horn sound to this set-up so I decided to add another sound card to the circuitry to provide a horn sound effect.

A suitable horn sound was tracked down on the freesound.org website and downloaded. It was then edited in Audacity to tidy up the sound and lengthen the sound of the second horn blast slightly (using the 'Tempo" tool).

It was then exported as a WAV file and uploaded to the new soundcard.

The wiring inside the main diesel loco was modified - basically, adding a second set of positive and negative leads to power the new card.  A speaker was fitted into the cab roof of the other diesel loco ....

.... and a new micro JST connector wired in to link the speaker to the output from the second sound card. This was wired-up in reverse to the first connector so it would be impossible to connect the two systems incorrectly.

To create space for the second sound card, the underside of the bonnet lid was hollowed-out. As it was 3D printed, this was a relatively easy job - the inside of the domed bonnet was already hollow but with the 3D default infill structure.

The cards were shrouded in insulation tape to avoid accidental short circuits.

The second sound card was wired up to one of the channel 5 output pads (Pad 6) from the Deltang Rx61b so the horn would sound when the bind button was pressed on the transmitter.

The loco was then given a test run to check all was well.

Using these sound modules is a relatively straightforward process but as only one track can be played on the card it is not very versatile. Being able to select different tracks stored on the card would enable a series of sounds to be played in sequence (eg engine start, idling, accelerating, running, decelerating, stopping, etc.). However, this requires a more sophisticated control system such as an MP3 player or  a micro-processors such as Picaxe or Arduino. For more information on using an Arduino-based sound system see - How I added sound to my Bluetooth controlled loco.