Nordic Star Products NRD24V1 - Manual (Page 8)

Revision 1.0 Page 8 of 25
User Guide
3.1.2 Micro controller
The micro controller is an AVR, ATmega88 and runs on a 4.096 MHz crystal. The micro controller’s main
tasks are:
• Setting up codec and RF circuits.
• Converting 16 bit PCB audio samples from the codec to 8 bit a-law samples to the radio circuit.
• Converting 8-bit a-law samples from the radio circuit to 16-bit linear PCM.
• Handling the RF protocol.
Additionally, five button inputs are scanned and one output is provided for driving. For example, this can be
used for an LED.
3.1.3 Radio circuit
The radio circuit (nRF24L01) is a complete radio transceiver for use in the unlicensed 2.4 GHz band. A 16
MHz crystal is used as a frequency reference for the RF. The RF output is matched to approximately 50
ohm at the antenna port. See section 3.1.4 ”Antenna matching network” below.
3.1.4 Antenna matching network
The RF output of the radio module is matched to approximately 50 ohm. An antenna is needed to set up
the RF link. There is a variety of different antenna types, please see section 4.1.1 ”Antenna” for more infor-
mation.
3.1.5 Power supply
The module needs a power supply in the range of 1.9 to 3.3 Volts. The module has been tested with a sup-
ply consisting of two ZinkAir cells (type 675) in series. Check the current consumption values shown in
Table 1. ”Electrical Specifications” below.
Note: Not all battery types are capable of handling the peak and average currents, even if the bat-
tery capacity is sufficient.
3.1.6 Programming
The module can be programmed using the ISP connector on the application board (see section 3.2 ”Appli-
cation board”), by connecting the appropriate pins on the module, or by using test probes on the corre-
sponding exposed vias on the back of the board.