Soundboard transmits .WAV files from the SD card as FM audio. Select a file from the list and press START, or enable Random mode to play files in random order.
File List
WAV files are loaded from the WAV/ directory on the SD card. Up to 50 files are shown per page; use the <= and => buttons to navigate between pages. The current page number and total files on that page are shown above the list.
Files must be mono and either 8-bit unsigned PCM or 16-bit signed PCM. The sample rate is read automatically from the WAV header — files sampled between 24,000 and 48,000 Hz work reliably. Stereo files and other bit depths are silently skipped.
Controls
- Loop (checkbox) — Repeats the currently selected file continuously until stopped.
- Random (checkbox) — Plays a randomly chosen file from the list each time START is pressed. When the file ends, a new random file is selected and played automatically.
- Key — Selects a subaudible tone to encode on the carrier. The full list includes standard CTCSS tones (labeled by EIA code, e.g. "1 XZ" through "50 ZZ") followed by wireless microphone pilot tones: Shure 19 kHz, Axient 28 kHz, Sennheiser 32.000 kHz, Sony 32.382 kHz, and Sennheiser 32.768 kHz. Select None (default) to disable.
- Vol — Controls the audio output volume to the speaker. Disabled (shown as
--) when a Key tone is active, since the pilot tone signal would be audible on the speaker. - START / STOP — Starts or stops transmission.
- Progress bar — Shows playback position within the current file.
RF Parameters
| Parameter | Value |
|---|---|
| Modulation | FM |
| Bandwidth | 1.75 MHz (baseband) |
| Sample rate | Read from WAV header |
| TX gain | 0–47 dB (LNA), 0/14 dB (AMP) |
The bandwidth field in the TX bar sets the FM channel bandwidth (deviation), not the WAV sample rate. The sample rate is applied automatically from the file header.
Preparing WAV Files
Files must be mono, 8-bit unsigned or 16-bit signed PCM, sampled at 24,000–48,000 Hz. The included sample files are 48,000 Hz / 8-bit. A quick conversion with sox:
for f in ./*.wav; do sox "$f" -r 48000 -c 1 -b 8 --norm "conv/$f"; done
In Audacity: mix down to mono via Tracks → Mix → Mix Stereo Down to Mono, then export as Other Uncompressed Files with Header WAV (Microsoft) and Encoding Unsigned 8-bit PCM.
Settings Persistence
Settings are saved to tx_soundboard.ini.