I have a Girafus 227PA Pet Tracking and want to create RF receivers that can be placed strategically in order to determine relative strength of the remote RF tag.
Locating the remote tag using the included handheld receiver requires activating the handheld receiver for the duration of the 'search' then disabling it again when the 'search' is complete.
To initiate a search the device must be calibrated each time by holding it in your hand and rotating yourself 360° around your own axis slowly multiple times while alternating the direction of rotation after each full rotation. If the remote tag is within range, the handheld receiver will successfully detect the remote tag's RF Signal (2.4GHz). If a minute elapses without successfully detecting the remote tag's RF signal, the handheld unit enters standby mode and you must then change your physical location with the hope of now being within range of the remote tag and then repeat the process until a signal is finally detected.
Once a signal has been successfully detected, gradually changing your location by walking in a relatively straight line while watching the handheld unit will allow you to determine through trial and error the general direction of the remote tag. You expect to see a stronger signal as you close your distance to the remote tag and a weakening signal as you move farther away (like playing "Hot or Cold'). Environmental factors such as structures can impact it's performance.
I would like to place some DIY receivers strategically that can communicate periodically (heartbeat) a relative signal strength which I can process server side to roughly map the location of the remote tag. This would allow me to have the relative location of the remote tag available in advance of requesting it, and also allow for mapping movement etc.
The remote tag uses a rechargeable battery which is expected to be recharged every 4 weeks with limited use. I expect anything I do will impact the battery-life of the remote tag and I will need to balance the frequency of data collection against the battery life.
In a July 2020 forum reply @petinox discussed his own project to determine the specific RF signals between the handheld unit and the remote tag.
(show/hide) @petinox's reply from July 2020
Hi,
RE: Replicating a signal from a locating device (2.4ghz) to locate tag
I would like to start by apologizing for the necromancy, I am aware that this post is five years old. I found this post while looking for information for a very similar project, and figured my progress so far would be useful for other people who do the same.I have similar tracker, the Girafus Pro-track-tor pet/cat tracker, and I believe the technology is close to identical.
The first thing you want to do is to open the device and look at the chip used. I tried looking at the public FCC data for your device, but the chip markings are smudged in the photos (this seems to be common practice). My device uses a CC2500 family chip from Texas Instruments, so I ordered some CC2500 modules from AliExpress.
The next thing you want to do is determine the frequency and modulation used in your device. I used a HackRF One to record some sample signals between the hand unit and tag. This gave me the precise frequency used. Then you need to look a bit at the signal to figure out other RF parameters, such as the modulation type used, BW, and data rate. It turned out my device uses MSK at 250 kbit. Universal Radio Hacker is useful software tool for this step, even though it does not explicitly support MSK.
For the CC-family chips you can get a CC debugger that lets you run the chips from a TI-provided piece of software called SmarRF Studio. This makes reverse engineering the signals much easier. The 250 kbit MSK turned out to be one of the suggested presets already set up in SmartRF studio, I only had to set the frequency and turn off CRC to get all the correct register settings for the CC2500 chip.
Now you can start to snoop on the communication between the hand unit and tag. In my case the protocol was very simple with some application id, tag id, command byte and probably link quality data sent back by the tag.
I then found some example code for arduino and the CC2500. I exported the chip register settings from SmartRF studio and modified the code, and was able to communicate with both hand unit and tag using a pro mini connected to the cc2500 module by SPI.
I hope this is of help to anyone starting on the same project!
Once I determine the signals exchanged between my existing devices. I will need to choose the hardware and software for the RF Receivers that are:
- plug-in and/or battery powered
- can be placed at various locations (e.g. behind or inside structures like garage, house, neighbors homes)
- can trigger RF signal detection at customizable intervals and communicate the relative strength data back to central location (RF? WIFI? Zwave?) to be processed server-side.
Synchronizing receiver scanning intervals might be valuable. Being able to manage the units remotely would also be useful (e.g. trigger a search mode where scanning frequency is increased. Exchanging the data with some kind of android or web-based location mapping app trigger actions (alerts, ongoing mapping etc.).
Sorry for the long post and I understand that there are a lot of pieces here and if you have some insight into one nook and not another I'd still be grateful.