On the main page, you’ve seen me talk a little bit about the idea of using predator sounds to scare elephants from crop-raiding and about where I placed these devices to accomplish that task. But HOW does the device work? This is a page that is going to be specifically devoted to answering that question.
Here’s a video that describes what should happen in an ideal situation.
And here is a video of what actually happened in one scenario when an elephant tried to walk through this area.
A case where things pretty much ran according to script. You can stop reading here if you were only interested in seeing the videos. For a more technical explanation, continue reading below.
You’ve seen the device in action where an elephant approaches a sound playback device and the playback happens. You know the general sequence and now, here are the individual steps that take place from elephant incidence in the area to sound playback.
1) A PIR (passive-infrared) sensor continually scans an area ahead of the speaker.
2) When a heat-emitting object (such as a warm-blooded animal) moves laterally across the sensor’s field of view, a signal is activated on a circuit-board. This signal is used to close an electrical connection using a MOSFET which then sends power to a speaker & mp3 playback device. The power will stay on for the duration of the signal, which can be customized and programmed on a micro-controller on the circuit board holding the PIR sensor – we have used a signal length of 30 seconds per trip event.
3) For as long as the power is supplied, the mp3 playback device will play a random .mp3 sound file from a USB flash drive chip through a speaker.
4) At the end of 30 seconds, the signal from the micro-controller to the MOSFET is cut and power stops flowing to the speaker and mp3 playback device. Only the PIR sensor remains active scanning the area ahead of the speaker.
5) Using this method where virtually all components are powered-off until needed, current draw is virtually nil (in the realm of a few milli-amperes) for the most part. Current draw when the system is active and playing back a sound is roughly 0.45 Amperes. Thus, power consumption for one trip event (30 seconds) is 0.45 A * 0.0083 h = 0.00375 Ampere-hours. Using our 12 Ampere-hour sealed lead-acid battery, this gives us enough capacity to power 3200 trip events. Now even taking into account the continuous power consumption of the PIR sensor, a single battery gives us enough capacity to power hundreds, if not thousands, of trip events. In the field, we’ve noticed that a fully charged 12-volt, 12 Ah sealed lead-acid battery lasts anywhere from 30 to 45 days before requiring recharge.