New Schematic - Rev C.4

[NZ0I]

With Rev C.4 the Dual-Band Transmitter schematic now includes all of the target features, including: 1-amp battery charging, and a socket for a GPS module. The schematic is available at the usual link: http://openardf.org/index.php/ardf-open-equipment-project/documents/

What's new:

An MCP73837 has been incorporated as the LiPo/Li-Ion charging device - it provides the added benefit of allowing a wall-wart to charge the battery at a faster rate than USB power can support.

Sockets for a GPS module will accept an AdaFruit GPS FeatherWing. I don't think most folks will want to use that $40 device in each transmitter, but the FeatherWing provides some features (battery back-up, and an enable pin) that will be good to experiment with. The FeatherWing could be replaced by a breakout board for one of the inexpensive "drone" GPS modules without too much difficulty - so this should make a good experimentation platform for GPS. 

With transmitter "cloning" support, which allows transmitters' clocks to be synced simply by attaching two transmitters with a short cable, I don't think there is as much benefit to having GPS time synchronization incorporated into each transmitter. So the GPS socket is there mostly to support experimentation. If $12 GPS modules can be made to work well in the transmitters, then there might still be incentive to use them there... but certainly anything we learn about cheap GPS in the transmitters will benefit the receivers.

Speaking of receivers, I will plan on adding the faster charging circuit, USB-to-UART interface, and GPS support to the receivers next.