16 Channel Sound Unit

Overview

This unit was designed to replay up to sixteen different recorded sound effects on radio controlled model boats, but will doubtless find application in other radio control projects. So far it has been used to great effect in several battleships to create various types of gunfire, sound horns and klaxons, make ASDIC 'pings', sound 'General Quarters', make aircraft and helicopter fly-bys etc. All the hard work is done by a commercially available embedded mp3 player module (the “DFPlayer Mini” seen in the picture above) and the unit’s microcontroller chip simply serves to decode a spare (proportional) radio control channel used to trigger the sixteen sound tracks. A radio controlled volume control has been implemented using a seventeenth channel.

The (user added) sound files are stored on a microSD card (uses 1GB to 32GB cards formatted FAT16 or FAT32) and the player supports MP3 and WAV files with all of the most common sampling frequencies (kHz): 8 / 11.025 / 12 / 16 / 22.05 / 24 / 32 / 44.1 / 48. The output is monophonic, and stereo tracks are represented as such.

A microSD card populated with demonstration tracks is supplied with the unit, and users can thereafter replace them with their own tracks via a card reader on their computer (internal card slot or USB gizmo). There are a great many sound effect libraries on the web from which sounds may be downloaded, usually in WAV format, so a good sound editing package like Audacity (free!) is handy if it is desired to convert them to MP3 format. It can also be useful to clean up lead-in or trail-out artefacts etc. and set the relative volume levels of the tracks with respect to each other.

The user selects the desired track number by a corresponding number of ‘jabs’ of the joystick, the sounds being arranged in two banks of eight on opposite throws of the transmitter joystick. Although many thousand tracks can be stored on the microSD card,given the track selection method it was considered sensible to limit the access to just 16 tracks. Selecting a track cancels any track currently playing and replaces it with the new one. Provision has also been made for a track to interrupt the currently playing one and when the interrupting track has completed the original track resumes playing from the point it left off. This feature is limited to a single interrupting track. A typical use of this would be to have a background ambience track or an engine sound which can be interrupted by a horn (but don’t expect the engine sound to vary in sympathy with the throttle – that’s a different animal!)

The user may optionally have a ‘wake up’ track which is played when the unit is first powered up.

The mp3 module also contains a built in 3W amplifier and will drive an 8 ohm loud speaker, either the mini type supplied or a larger one provided by the user. A 20 step volume control is provided, accessed by 9 ‘jabs’ of the joystick in the appropriate direction, the volume level finally set being stored in memory and re-asserted at power up.

Features:

• plays 16 sounds from a single proportional RC channel
• sounds arranged in 2 banks of 8 to either side of the joystick
• 20 step volume control
• integral 3W amplifier
• supplied with 8 ohm mini speaker and 4GB microSD card containing example sounds

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