Introduction
This is the documentation of the ahoi acoustic modem. It includes a description of the hardware, how to use it, and what equipment you need to get going. It also entails tutorials that explain, step by step, the basic functionality, features, and available software tools. The ahoi acoustic modem is an open-source device, and this documentation will support you to build your own, to set it in operation, and to use it successfully.
Legal Notice
THIS DOCUMENTATION IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Hardware
The hardware comprises a stack of three boards: a mainboard with a microcontroller (blue), a receiver (green), and a transmitter (red). All boards follow a trade-off between high integration to achieve a small overall footprint and easy assembly by hand. We rely on COTS components exclusively, which were easily sourceable at the time of development. Component lists are provided along with schematics.
General properties
The ahoi modem features the following properties in its default hardware configuration and with our open-source firmware.
| Property | Value |
|---|---|
| Dimensions (wlh) | 50 mm x 50 mm x 22 mm (stacked PCBs, w/o battery and cables) |
| Weight | 30 g (PCBs only) |
| Frequency Band | typ. 24 - 60 kHz (depending on configuration, max. 20-96 kHz) |
| Bandwidth | 24 - 36 kHz (depending on configuration) |
| Data Rate | 250 - 4,500 bit per second |
| Transmit Power | up to 5 W (down to 0.75 W) |
| Receive Power | ca. 260 mW |
| Range | 300 m shown in experiments (potentially more than 1 km) |
| Supply voltage | 12V (3S Li-ion Battery) / max. 13V |