View Full Version : How does a GPS chip work? Does it need batteries? Do the batteries need replacing?

Plot Device
01-26-2011, 07:37 PM
If you chip'd either a dog or a horse or a human being with a GPS tracking chip, would it fuction forever, or would it need to be replaced every now and again?

Drachen Jager
01-26-2011, 08:22 PM
It needs a battery. I do not know how long a battery would last but, presuming you had a system where it could be turned on remotely a battery may last for years.

Plot Device
01-26-2011, 11:43 PM
It needs a battery. I do not know how long a battery would last but, presuming you had a system where it could be turned on remotely a battery may last for years.

Assuming it cannot be truned on and off remotely, how log can a battery last? Two years??

01-27-2011, 12:22 AM
If you're talking about a subcutaneous tracking chip (under the skin), those haven't been developed yet.

01-27-2011, 01:23 AM
There are several components here.

1) GPS receiver. It receives signals from satellites and as long as the antennae can see satellites, it can compute a position on the surface of the planet.

2) Emitter. You need some kind of radio link back to a base station so the collar can tell it "hey, I'm here. Now I'm here, etc". It could be based on simple cellphone communication, either like a cellphone uploading some text on Twitter at regular intervals, or more like the emergency beacons found in rafts that emits a broadcast signal (also called PLBs - Personal Locator Beacon).

Regardless of the techology, you will have to trade battery weight for range, duration, and update frequency. For example, a cellphone that transmits its position every 5 minutes might last 72 hours. But you need to be within range of cellphone base stations, not in the middle of a forrest. A PLB might last 48 hours, but it has a long range (100 nautical miles) and a large battery pack.

Animal collars have very weak signals. You need to be within 50 yards or less to pick up the signal, which is no more than a series of pulses that correspond to a unique ID. But depending on the collar size, those may last a few years.

More context might help narrow the tech and what can be done.

Hope this helps.


01-27-2011, 04:04 AM
If you basically use a cellphone, just stripped of everything not required to send location and id (and calculate the location in the first place) you'll end up with a device not significantly larger than the cellphone battery that can last a few weeks. What you basically need, besides the battery, is an antenna to pick up the GPS signal and transmit the location and ID to the next cellphone tower, as well as a specialized chip that calculates the location. Both can be made pretty small, the battery is the largest part. So, take the battery out of your cellphone to get a good visual impression of 2 weeks lifetime for the device. For four weeks, you'd need two of those batteries, etc.
If you want it to transmit via satellite so it can function even in the middle of a desert, it will need a significantly larger antenna and have much shorter battery life. Check out satellite phones for comparison to a normal cellphone.
A simple RFID chip would be inert (i.e no batter), but it only work by getting close to the appropriate reading device, which will then be able to pick up the ID of the chip at a distance of a few meters (at most).

Mac H.
01-27-2011, 01:01 PM
If you chip'd either a dog or a horse or a human being with a GPS tracking chip, would it function forever, or would it need to be replaced every now and again?It needs batteries.

A typical GPS module is sized about 30 x 30 x 10mm and consumes around 220mW.

Some batteries:
A lithium 9v battery could be up to 10800 mWh .. giving a life of 49 hours
A 'coin cell' battery could be up to 480 mWh .. giving a life of about 2 hrs.

For simplicity I've ignore inefficiencies in power conversion and the fact that you'd want to send the data somewhere (unless you were simply logging it for later use)

Putting the device to 'sleep' and only waking it up every hour or so to log data would extend the life significantly ... although they typically have a 45 second 'cold start' reacquisition time .. so you'd have to keep it powered for a minute just to get a decent fix. But if you turned it on once per hour you'd extend battery life a lot.

If you wanted it to be done to someone secretly you could still do it.

Just put an inductive charging coil in the person's bed and recharge the battery inductively every night - along with downloading the data from the GPS.

That way - as long as they return home you could log everywhere they went that day.


There are other (quite clever) approaches. One uses accelerometers - which are normally quite inaccurate for location because it relies on a double integration to convert to position .. which just emphasis any noise.

However if implanted in the user's leg than it instead models the user's gait based on the accelerometer data ... so it can guess that you took a step of around 30cm forwards. It can then integrate to get position.

An accelerometer IC takes only about 3 mW instead of 220mW .. so is a huge power saving.

There are some other technologies that haven't been generally released yet.

(PS: I know this isn't the level of detail that you want .. but it just gave me the chance to geek out on a subject that I'm familiar with!)

Plot Device
01-27-2011, 05:05 PM
Posted long response.

Internet went down.

Long response lost

Rolls eyes.

Begins again.

Plot Device
01-27-2011, 05:18 PM
A huge thank you to all my fellow geeky writers and their geeky techy replies here (especially Mac H. :D).

Meanwhile, as cbenoi1 pointed out in his own very astute Post #5 above, a little context might be helpful.

And here's the part where I say "Darnit! Why do I always tell myself I can just sneak into this sub-forum, ask my question, then make my getaway with a huge cache of the needed info WITHOUT ever having to divulge my plot details?" And it's not that I'm one of those paranoid writers who fears her ideas gettig ripped off. Its just that when you're writing sci-fi, the ideas can sound kinda hoaky when explained out of context. So I fear ridicule more than theft.

Anyway ... hre's my plot detail with some brief context.

My story takes place about 5 years in the future (so I have some leeway to make stuff up as far as technology). My MC discovers he has an implant he never even knew about. He has it yanked out by a dcotor, then takes it to a techy-geeky friend who can hopefully tell him what it is. His friend recognizes certain components of it as GPS tech. But then he realizes certain other components are a form of technology he assumed was still only theoretical. Specifically, the GPS has no batteries, and so it instead operates off of the bio-wattage that gets naturaly generated by the human body. Therefore the GPS could work for years any not need replacing.

Here's a science article dated 8 years ago in the Sydney Morning Herald which discussed this sort of tech.


Power from blood could lead to 'human batteries'August 4, 2003

August 4, 2003

A device that produces electricity from blood could be used to turn people into "human batteries".

Researchers in Japan are developing a method of drawing power from blood glucose, mimicking the way the body generates energy from food.

Theoretically, it could allow a person to pump out 100 watts - enough to illuminate a light bulb.

But that would entail converting all the food eaten by the individual into electricity. In practice, less power would be generated since food is needed by the body.

However the scientists say the "bio-nano" generator could be used to run devices embedded in the body, or sugar-fed robots.

The team at electronics giant Panasonic's Nanotechnology Research Laboratory near Kyoto has so far only managed to produce very low power levels.

But the scientists ultimately expect to gain much greater performance from the device.

The battery is based on an enzyme capable of stripping glucose of its electrons, The Engineer magazine reported.

Dr Kazuo Eda, heading the research, said: "It is like the metabolism of food. Human bodies can process glucose and obtain energy. When glucose is oxidised, electrons can be obtained."

He believed bio-nano fuel cells were the next step for researchers after generators powered by hydrogen, natural gas and methanol now being developed for the car and energy industries

01-27-2011, 07:34 PM
There are those watches that are powered by electricity generated by the body, perhaps some version of that?

Drachen Jager
01-27-2011, 09:33 PM
There are watches powered by kinetic energy as you move around, I don't think there are watches powered by your electrical field. I could be wrong, but my understanding is there is not enough electrical difference on the surface of the skin for anything like that.

01-27-2011, 10:26 PM
the GPS has no batteries, and so it instead operates off of the bio-wattage that gets naturaly generated by the human body. Therefore the GPS could work for years any not need replacing.

The GPS can run on very low power requirements since it's simply a receiver. To send the data collected by the receiver to some other source, that's what will take the power. I think the bio-battery concept is fine for powering the GPS. I think you'd need something more to transmit the data. You could use a micro transmitter to transmit the data a very short distance, like to a fancy wrist watch that our protag always wears. But, it turns out this fancy watch has a more powerful transmitter in it, cell phone or otherwise, that then retransmits the data to our bad guys. That watch could have some pretty decent batteries in it. Or, make it go to his actual cell phone that he always carries. RFID would work for that. The watch or the cell phone would be close enough to power the RFID chip (or an extension thereof) and that RFID-like device would then transfer the data to the phone or watch. Just a thought.

Also, GPS is a term that describes the US navigation satellite system. GNSS or Global Navigation Satellite System is the generic term for such navigation satellite systems. The Russian system is called GLONASS (I have no idea what the acronym means), the British system is called Galileo, and India and China and Japan are working on their own systems. GPS is owned by, and controlled by the US. We can turn it off, or scramble it if we need to. Anyway, many modern commercial navigation systems are tracking both GPS and GLONASS now, and many more will track Galileo once it's operational. Something to consider -- but may be TMI. :)

01-27-2011, 11:20 PM
The circuit could be using inductive charging ( http://www.springerlink.com/content/u71m34lh53044502/) to charge up the battery. Say your MC goes to a tanning once a week or works near high-current sources. The amount of EM energy going through the coil could be enough for a full recharge.


Tsu Dho Nimh
01-29-2011, 05:29 AM
If you chip'd either a dog or a horse or a human being with a GPS tracking chip, would it fuction forever, or would it need to be replaced every now and again?

There are two kinds of tracking chips:

Active, like the tracking collars they put on polar bears, require batteries because the transmit the location to whoever is doing the tracking.

Passive, where you track the chip as it goes past a powered detector (dairy cow ear chips, the ID chip in pets, etc.) last a very long time and do not require batteries. But the chip reader does. And the range is limited.

01-29-2011, 07:59 AM
Just for the record... that doesn't sound hokey, it sounds completely plausible, if pulled off right. ;)

As the others have mentioned, the problem is going to be the transmitter power requirements. Having the cell phone/watch relay coordinates is, if I may be so blunt, a complete waste of money. Just put the tracking chip in the watch! I mean, seriously, think like an engineer here. Cost-effective. Don't be redundant! ;)

So, in other words, there's really no reason to separate the two. The system is only as good as its weakest link--in this case, the external component.

But you still have the issue of power draw. Your best bet is probably going to be having a trickle-charge capacitor that stores up juice until it has enough to fire off a short transmission. I have no clue how much power you can draw from the blood, but cell phones usually draw between 0.6 and 3 watts to transmit. Text messages should be on the lower end of that, but let's go with a conservative 0.5 watts.

The article says you can theoretically get up to 100 watts of power from the whole human body. You of course won't be able to, because the individual would die, but let's say the device was attached to an arteriole feeding at a rate of 4.6 nanoliters/second (the only number I could find for the flow rate of an arteriole--a "given" value for a homework assignment, so take it with a grain of salt). Given that the average human has about 5 liters of blood in their body, we're looking at approximately one trillionth of the power of the person's whole body.

Assuming the 100-watt figure mentioned above, that puts us at 0.1 microwatts per second per arteriole. With only one arteriole, it will take about 5 billion seconds to charge up to enough power to make a transmission.

That's an unacceptably long time.

An artery, on the other hand, has a flow of about 8.3 mL/s (again, this number comes from a given on a biology problem [actually, it's a calculation based off of two separate biology problems], so take with a grain of salt). Following the calculations above, that should give you a more reasonable 0.166 watts per second, but keep in mind you can't use all of that or things will start dying. No matter, if you only draw 10 mW/s, you'll reach 0.5 W in under a minute. Location updates in one-minute increments should be feasible, right? It would be even safer to drop that to 1 mW/s and just do updates every ten minutes, but that's up to you.


I have absolutely no clue if any of that math is at all valid, because I'm going almost entirely off of numbers that I found in random places on the Interwebz. But then, doesn't everybody? ;)


Tsu Dho Nimh
01-30-2011, 01:09 AM
Skyler - Good idea. There are intermittent transmission tracking devices that only collect info and transmit as a burst when the conditions are "right" ... such as they are at the surface of the ocean, they just got hit by a pulse from the controlling device, or they have enough power to send.