Circuits and Systems

Hello again! This has been a really slow week, due to almost everyone else being out on Spring Break, so this won't be too long of a blog post. Try not to celebrate too much about that!

Battery life is something that pretty much all of us think about. Laptops, phones, and iPods are just a few things that we constantly have to keep track of to make sure that their batteries aren't dead when we need them the most. The batteries that I just mentioned are relatively easy for us to recharge or change, but imagine if the batteries on an animal tracking device needed to be charged as often as a smart phone battery! The whole point of using tracking devices on wild animals is to be able to observe animals in their natural habitat without human interference, and a device with batteries that need to be changed more often than once every couple months necessitates too much interaction between researchers and the animals.

Sure, we could have all the battery power that we could possibly need if we use a giant car battery... but that's not very practical for any device on an otter. I read somewhere that a good goal for anybody designing a device to track animals is to have the device weigh less than 1% of the animal's body weight. Therefore, any device that would be attached to a sea otter would have to be extremely energy-efficient, because battery weight makes up a fairly high portion of any tracking device's total weight.

When using a triangulation system, energy-efficiency is easy to achieve. The device simply needs to put out a pulse at a certain radio-frequency about once every second (or more often). These devices can last for years, like the abdominally-implanted VHF devices currently in use for sea otters. However, when we try to use GPS or multilateration systems, the power required to have the system running constantly is unsustainable for periods longer than a couple days, and either a low-power sleep-mode or an on/off mechanism is necessary to achieve greater longevity. Here's a circuit diagram for a proposed device by last year's golden lion tamarin senior design team:

If you don't understand this diagram, don't worry. I don't fully understand it either, but arguably the most important piece to those of us trying to make devices power-efficient is the 32KHz clock that works with the MicroController. Ideally, when a location on the device is not needed, the only power-consumption by the entire device will be by that clock, which wakes up the device at specified times in order to determine a location. This specific circuit diagram is for a GPS-enabled device. 

Which is more battery-efficient, keeping the tracking device in a low-power sleep-mode when not in use, or turning the device on and off each time it needs to transmit? This is an important question because sometimes turning on the device can require a lot of power. Also, where, if at all, does solar-power technology fit into a sea otter tracking device? These are questions that I'm hoping to learn the answer to in the next week or so. Until then, I hope everyone else is enjoying their spring break (or not, sorry fellow seniors)!