cat-tracker

A multi-function application designed to run on a pi node. When used in a mesh network, this app will help track your cat with a CC2500 based radio collar, using complementary CC2500 based radio modules interfaced with your Pi.

The implementation here uses CC2500 register values which intend to mimic my Girafus M07A unit. This unit is paired with my associated tracker

Links

• Arduion Forum Port
• cc2500 data sheet
• C Code transciever example

CC2500 to Raspberry Pi GPIO Pin Mapping

CC2500 Pin	Function Description	Raspberry Pi GPIO Pin	GPIO Number
GND	Ground	Pin 6	-
VCC	3.3V Power (⚠️ Do not use 5V)	Pin 1 or Pin 17	-

SPI Connections

CC2500 Pin	Function	Raspberry Pi GPIO Pin	GPIO Number
SI	MOSI	Pin 19	GPIO 10
SCK	SCLK	Pin 23	GPIO 11
CSN	CE0 (Chip Select)	Pin 24	GPIO 8
SO	MISO	Pin 21	GPIO 9

Optional Pins

CC2500 Pin	Function	Raspberry Pi GPIO Pin	GPIO Number
GDO0	Interrupt/Data Ready	Pin 12	GPIO 18
GDO2	Additional Interrupt/Data Line	Pin 22	GPIO 25

Power Amplifier Pins (If Applicable)

CC2500 Pin	Function	Raspberry Pi GPIO Pin	Notes
PA_EN	Control Power Amplifier (Optional)	Any GPIO Pin	Connect if amplifier control is needed
PA_EX	Reserved	Not Connected	Only connect if required

Reverse Engineering the Registers

SmartRF Studio

Install

SmartRF Studio will automatically generate a configuration for the CC2500 Radio based on some RF parameters

• A free registration and login is required to download this app from Texas Instruments
• The app seems to run well via wine on linux. I chose to install it on an actual Windows OS, then copy the binaries.

Copy Register JSON template

When this is installed, copy the code export json file to help export the initial register configuration in a JSON format

cp srfexp_json.xml "~/Documents/Texas Instruments/SmartRF Studio v7/codeexport/."
# Example copy command for linux+wine 

Understanding necessary RF Parameters

In SmartRF Studio, open the CC2500 Device Controller under the 2.4 GHZ list.

At the time of writing, it is believed this device uses 250 kBaud MSK encoding. We will choose this option.

Next we need to figure out the Base Frequency, Channel numbers, and Channel Spacing

Singal Capture

I have captured the initial signal emitted by the handheld unit when it is first powered on. To do this, I have used a HackRF SDR + gqrx application on linux.

The known frequency range is 2400 – 2483.5 MHz, and my SDR has a 20 MHZ bandwidth. I choose sweep for signals by tuning the following frequencies

Sweep #	Center Frequency	Center Frequency (kHz)	Approx. Coverage (MHz)	Approx. Coverage (kHz)
1	2410 MHz	2,410,000 kHz	2400 – 2420 MHz	2,400,000 – 2,420,000 kHz
2	2430 MHz	2,430,000 kHz	2420 – 2440 MHz	2,420,000 – 2,440,000 kHz
3	2450 MHz	2,450,000 kHz	2440 – 2460 MHz	2,440,000 – 2,460,000 kHz
4	2470 MHz	2,470,000 kHz	2460 – 2480 MHz	2,460,000 – 2,480,000 kHz
5	2483.5 MHz	2,483,500 kHz	2473.5 – 2483.5 MHz	2,473,500 – 2,483,500 kHz

Signal 00

2.423257000 GHz | 2423.257000 MHz | 2423257.000 kHz |

Signal 0

2.431258000 GHz | 2431.258000 MHz| 2431258.000 kHz

Signal 1

2.447257000 GHz | 2447.257000 MHz | 2447257.000 kHz

Signal 2

2.450225000 GHz | 2450.225000 MHz | 2450225.000 kHz

Signal 3

2.471275000 GHz | 2471.275000 MHz | 2471275.000 kHz

Signal Summary

• Base frequency: ? MHz
• Date Rate ? Baud
• Channel spacing: ? kHz
• Signal channels:
• Signal 00 → Channel ?
• Signal 0 → Channel ?
• Signal 1 → Channel ?
• Signal 2 → Channel ?
• Signal 3 → Channel ?

Run

python3 read.py