I thought to use ever popular module with NRF24L01 transceiver ic. But I don't have small one, one with 8 2.54mm pin connector is huge and will never fit inside a gamepad.
INHAOS Technology Co. This will fit nicely. It has the same configuration registers, but has 2 register banks. Second bank is only to configure BK2421 ic.
OK. Now I need a microcontroller to make it all work. I have 2 spare MSP430G2452 in VQFN package. This is enough to make proof of concept.
Also I need a battery for gamepad, lithium rechargeable battery. I will use MCP73831/2 charging ic from Microchip to charge this battery from USB.
In the next part I'll make schematics for transmitter and receiver modules.