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does anyone know if it is possible to buy or build a really small tracker that uses wifi only.

I'm hoping to begin a masters studying bats, possibly in China, I expect in China the areas that the bats fly around will be at least partly covered by the wifi network. GPS is still mostly too large for 50g bats, radio tracking would work but then I need to chase them and find out where they are and would have a lot less data points. It would be nice to just be able to recatch them and download approximate data of where they went from a microSD. I expect someone might sell this type of thing somewhere (probably in China :) ) but if not I have built things before so I would be interested in basic suggestions for how to go about that too, just not sure if I could make it small enough if I was doing it myself.

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  • \$\begingroup\$ Strap a ESP8266 to a large enough flash. \$\endgroup\$ – Ignacio Vazquez-Abrams Oct 24 '16 at 20:59
  • \$\begingroup\$ p.s. if anyone has any total different suggestions for suitable systems I am interested in that too. I also would like to measure temperature and/or heart rate of the animals but I will think about that later. \$\endgroup\$ – shara Oct 24 '16 at 21:01
  • \$\begingroup\$ @Ignacio, thanks!, just about to go out but will look that up when I get home :) \$\endgroup\$ – shara Oct 24 '16 at 21:02
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    \$\begingroup\$ Whatever you are going to build, the battery is the part which is most bulky. Wifi is not going to work because it eats battery as much as GPS does. Really, having a small transmitter on the bat which just gives a ping every few seconds or so and triangulating it is the only chance you have at this. \$\endgroup\$ – Janka Oct 24 '16 at 21:03
  • \$\begingroup\$ Some of those ESP8266 wifi devices are very small -- an antenna and a small can. But then there is power. But I still think it would be very annoying to bats and I would worry that it might significantly affect their behavior. \$\endgroup\$ – jonk Oct 24 '16 at 21:03
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I don't know if it fits your data throughput needs, but you might want to look at lower power protocols such as Bluetooth Low energy (BLE), Zigbee, or Xbee. They tend to be lower power consumption, and lower throughput than wifi, but also various range options (some longer than typical wifi). In general the lower the data throughput, and lower the range, the lower the power requirements. If you know within 1-100 meters of where your bat is going to end up in general, I'm imagining a known cave, you might be able to lower the range and power requirement quite a bit and download data from where they rest.

If you drop the RF requirement altogether, and just data collect in very small amounts, something like an MSP430 with FRAM could take very little power.

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  • \$\begingroup\$ Shara wrote the area is probably covered by mobile networks so most likely not a cave but a city. \$\endgroup\$ – Janka Oct 24 '16 at 22:52
  • \$\begingroup\$ Ah, but do they return to the same place to rest? If that's the case you might be able to download wirelessly at a low range where you originally tagged the bat. I guess there's some uncertainty with respect to needing RF transmission, or if Shara is planning to just re-catch and download data (maybe RF is just a nice to have...) \$\endgroup\$ – Digikata Oct 24 '16 at 23:20
  • \$\begingroup\$ If I understood this correctly, the usual method to do this kind of behaviour research is indeed to put small ping senders on the bats, but instead of triangulating them, people go hunt the signal until they got the highest readout. Maybe use a rotating dipole antenna to get a direction to go. That works but gives only a few waypoints as the bats move, too. Having GPS or Wifi cell or phone cell detection on the device would make locating the trace of the bat easier. \$\endgroup\$ – Janka Oct 24 '16 at 23:25
  • \$\begingroup\$ @Janka & Digikata, yes I'm hoping to be able to recatch the bats after recording to an SD card or other memory device automatically. I was thinking of using a separate small radio device as well to find the bats in order to remove the electronics and download data. If they come back to the same roosting place each day then I might not use radio at all ideally. I have two species in mind one of which roosts in trees and one in caves but both would spend some time out looking for food in farms/cities which are likely to be in wifi range at least partially. \$\endgroup\$ – shara Oct 25 '16 at 3:03
  • \$\begingroup\$ @Janka & Digikata, thanks! yes I'm hoping to recapture the bats in order to download data. I was thinking of possibly but not definitely using radio but only in order to help find them to recover the electronics. If I could triangulate using the mobile network or similar and automatically save this to memory I would get a lot more data points. I have two species in mind, one is tree roosting and the other cave roosting but both would spend time flying over the city or nearby farms I think. \$\endgroup\$ – shara Oct 25 '16 at 3:11
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I worked on something similar to what you describe, for animal tracking. From your description it seems like you can re-capture the animals which is key. The high power usage of Wi-Fi is mostly from transmitting, which is not needed to get location. Using an esp8266 and a microSD I was able to get location with less power on average than a typical GPS.

The main limitation is that you need to know if there is data on the wifi hotspots in the area. There needs to be enough to triangulate a position, the more the better. The hotspots also need to be in some kind of database. I used the google API for location, which did the hard work for me. The google API is nice because it also gives you the error based on how many hotspots were used to triangulate.

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  • \$\begingroup\$ thanks very much, this looks possible if I can make it, will look into it :) \$\endgroup\$ – shara Oct 25 '16 at 3:05
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Due to Friis Loss increasing with distance squared and increasing frequency, lower RF frequencies are preferred not WiFi which like Bluetooth is only good for 100ft but weight is too high and signal loss too great.

Therefore get high gain receiver antenna and very low noise threshold high performance receiver in the 50~150MHz range

https://atstrack.com/tracking-products/transmitters/product-transmitters.aspx?serie=A2405

enter image description here

have fun

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