I have lost FPV plane due to pilot error. It ended somewhere inside nice deep forest. Battery was probably disconnected during “touchdown” and OpenLRSng integrated beacon was not working. First and only plane lost in my 10 years of FPV….
After researching available solutions both opensource and commercial I decided I like CoolBeacon / tBeacon approach. It is based on familiar RFM22b module and Atmega328. For both CoolBeacon / tBeacon hardware is sort of compatible with OpenLRS. By some dark magic, authors get digital FSK based transceivers to transmit FM modulated voice. It is distorted but still pretty readable.
Friend of mine is building tBeacon compatible hardware out of plain Arduino Mini and RFM22b module by dead-bug method. It is tedious and missing some features. I decided to make my own boards.
I started with my existing design for OpenLRS MicroRx I am already using. I have redrawn schematics to fit both firmwares, added battery / power management IC from STmicro.
Power management circuit STNS01 does all the magic. When external 5V is turned on, it turns on power to the board and starts to charge battery. If plane crashes and main battery is disconnected beacon continues on internal battery. STNS01 also provides standard Lithium battery protection features. After successful flight button on Beacon is pressed for ~1s and STNS01 is put to “shipping state” where everything is off and standby current is around 500nA. Only way to bring it back to life is to connect valid external voltage. This is drawback as beacon cannot be turned ON without external voltage.
Schematic is pretty self-explaining. Also the layout. I have placed integral balun ETC1-1-13 on board for easy dipole antenna fabrication. Basically one wire goes up, second down.
I have also ordered stencil to ease the manufacturing.
Notice electrically short antenna tuned to desired frequency