by Lance Looper, Campaigns and Community, Silicon Labs
Several years ago, a group of graduate students at the University of Southampton, along with Professor Alex Rogers, now at the University of Oxford, set out to use their smartphones to record the songs of a possibly extinct cicada in the forests of the U.K. The cicada sings at a very high frequency, at about 15 kilohertz, which most adults can’t hear — but smartphones can. Although the group was unsuccessful in recording the insect, during the process they built AudioMoth, a small, low-power acoustic device that filled an unknown void for wildlife conservation. After launching the device to the public a year ago, it is now so popular among ecologists and conservation organizations that members of the team are building a company around the device, called Open Acoustic Devices.
AudioMoth is used to track and study hard-to-detect wildlife, such as bats, birds, and insects and/or potential threats to wildlife, such as gunshots by illegal poachers or chain saws in protected forests. The device uncovered a huge appetite for low-cost, open source acoustic recorders from ecologists and conservation organizations, who were previously limited to either using expensive commercial recording equipment or excessive battery constrained devices.
The price disparity for an ecologist is compelling. A highly sensitive audio recorder for field research costs close to $1,000 per audio recorder. Cheaper open-source recorder options exist, built from a low-cost single-board computer, but they require massive battery packs for researchers out in the field for lengthy periods of time — sometimes even car batteries! The AudioMoth, on the other hand, is slightly larger than a smart phone (batteries included) and costs roughly $50.
The cost advantage of AudioMoth is completely changing the science people can do. Previously, if an ecologist had a small budget (which many do), they could maybe only deploy three or four recorders. Now researchers can potentially deploy 100 recorders, meaning different types of wildlife surveys can be conducted, opening the door to broader research that would have been cost-prohibitive before.
Building the device
The brains behind the device include PhD students Andy Hill and Peter Prince, along with Professor Rogers, who regularly works with his students to explore new technology for biodiversity monitoring. With the AudioMoth team, Rogers said they were looking to create a minimal device that could run smart algorithms to only record when hearing a sound of interest. In this instance, it was the sound of a New Forest cicada.
The students combined a cheap MEMS microphone, similar to what’s inside a smartphone, with an SD card and MCU to create a programmable and highly mobile device. Because of the small size, the microphones are extremely sensitive to high frequencies – perfect for people interested in bats, where they are recording at 100 kilohertz.
Rogers said they knew from the beginning they had to focus on low power, as wildlife research users worry most about how much data they will end up recording, as they are often sitting for hours or days before anything happens. To address the extreme power needs of the device, the students decided to use Silicon Labs’ Wonder Gecko MCU processors due to their low power capabilities, which result in smaller batteries and longer life in the field.
The non-commercial open-source recorder alternative is typically based on Raspberry Pi, an alternative using a much more capable processor running a Linux operating system, but as a result requires a much larger battery pack. In many wildlife applications, the devices have to be carried to the deployment sites in backpacks, making the size and weight of the batteries critical.
To put the power usage gains in perspective, Open Acoustic Devices has a current deployment in Belize that involves listening for gunshots to detect illegal hunting in tropical forests. With a small battery pack (a 6V lantern battery), the user can deploy a sensor that lasts for 12 months and listens continuously for 12 hours a day, only making recordings if it thinks it detected a gunshot.
The Gecko MCU allows for nearly all of the listening to occur while the processor sleeps, then the chip wakes up to run the detection algorithms across a 4-second sound buffer. According to Rogers, this key feature, along with Silicon Labs’ integrated tool chain, was a key factor behind the processor decision for the device because it directly measures and optimizes energy consumption and distributes the free code.
Hacking low volume manufacturing
In order to keep costs low and get the device to market, the students started exploring alternative manufacturing routes. With Alasdair Davies of the Arribada Initiative (an organization promoting open affordable conservation technology), the team started running group purchasing campaigns through GroupGets, a low-cost assembly company that facilitates group purchasing. After testing the market with some relatively small orders, GroupGets enabled Rogers’ team to run off a batch of 1,500 devices from a PCB assembler, providing real economy of scale.
The unique model allows designers the ability to offer various types of devices, yet manufacture at low risk. So far, Open Acoustic Devices has manufactured close to 4,000 devices and is currently manufacturing the next 1,500 for a campaign that has just closed. As a small university project, Rogers said there is no way the team would have been able to manufacture the devices without this model.
They also used CircuitHub, which enabled the students to post the hardware design and bill of materials on the CircuitHub website. As Rogers explains it, the concept essentially hacks low volume manufacturing. Suddenly, people can share and distribute hardware in the same way people have been able to share and distribute software.
IoT meets the jungle
Despite the fact that many of the deployments of the device are in remote jungles and forests with extremely limited Internet access, Open Acoustic Devices is still planning to add low-power wireless connectivity to new versions of the device for alerting, streaming and research purposes.
Rogers said the team is optimistic about the new science and data the device will uncover for wildlife conservation, and he is confident adding connectivity to the device will make the device all the more powerful for conservation efforts as scientists can share and compare their work collectively.