Nordic Star Products NRD24V1 manual LED Buttons

User Guide

Audio DAC

Out

Audio ADC

In

Application

Voice

Protocol

MCU

I/O

Buttons LED

ShockBurst

I/O PHY RF

ShockBurst

PHY I/O RF

Application

Voice

Protocol

MCU

I/O

LED Buttons

DAC Audio

Out

ADC Audio

In

Figure 4. System diagram of headset unit with audio dongle configuration

The headset unit and the audio dongle are based on the same hardware. Both use an audio codec to pro- vide coding and decoding of the analog audio signals to 16-bit linear PCM code. This bit stream is pro- cessed by the micro controller to an 8-bit a-law bit stream, which is sent to the nRF24L01 for wireless transmission. The nRF24L01 uses the ShockBurst feature to transmit and receive the RF packets in a time multiplexed scheme. The micro controller fetches received 8-bit a-law samples from the nRF24L01, con- verts to 16-bit linear PCM, and outputs to the audio codec. Button status is read by the MCU and embed- ded in the RF packets.

The USB Dongle uses a USB Audio Controller to handle the USB interface. The audio samples are 16 bit linear PCM between the USB Audio Controller and the micro controller, where the micro controller acts as a bus master. The audio frame signals are derived from clock output from the USB Audio Controller to keep the audio frames in sync with the USB audio frames. The micro controller can also access the USB HID interface through the I2C bus, also with the micro controller as the bus master. The USB HID interface is used to upstream button status received from the headset to the USB host. The micro controller converts the 16 bit linear PCM code to an 8-bit a-law bit stream, which is sent to the nRF24L01 for wireless trans- mission. The nRF24L01 uses the ShockBurst feature to transmit and receive the RF packets in a time mul- tiplexed scheme.

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