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Revision 1.0

Page 17 of 25

Headset Reference Design v1.0

4       Hardware design guidelines

This chapter describes important issues that might affect you when developing the headset reference 
design for a finished product. The USB dongle can be used as-is, but the headset must be redesigned to fit 
into a headset for a finished product. However, the radio module mounted on the headset can be used as-
is together with the audio interfaces from the application board.

Note: 

Most radio regulations do not allow more than 0dBm output power without doing proper fre-
quency hopping. Adding a PA to this design requires a major re-design of the radio protocol 
because the headset reference design uses a frequency agility protocol.

4.1        Headset

The radio module is used as-is in the headset design, but it must be interfaced in a way that ensures opti-
mal performance.

4.1.1        Antenna

The radio module is connected to the antenna on the application board. This antenna does not fit into a 
headset design for a finished product, so using the radio module in a headset application for a finished 
product will require a different type of antenna. 

In a headset application for a finished product, the radio module must be mounted on a PCB with an 
antenna terminal. On this antenna terminal, any 50 ohm 2.4GHz antenna can be used, from an inexpen-
sive PCB antenna to space saving chip antennas. 

There are different types of PCB antennas, from inverted F antennas to simple quarter wave antennas. 
You must know the characteristics of the chosen antenna and implement it as required. Tuning the 
antenna will be necessary because an antennas impedance and performance is affected by the environ-
ment the antenna is used in.

Using a chip antenna must only be done according to the chip antenna vendors recommendations. 

The radio module is equipped with the recommended antenna matching network layout for the nRF24L01. 
When operating from the application board, the radio module’s antenna matching network is tuned to 
match the application board antenna impedance.

When using the radio module in a headset application for a finished product it is important to tune the 
antenna matching network to match the impedance at the antenna’s terminal. Another important task of 
the antenna matching network is to suppress spurious energy. You can achieve this by following our white 
paper called “Tuning_the_nFR24xx_matching_network” available on our website 

www.nordicsemi.no

.

4.1.2        Interfaces

4.1.2.1        Buttons

Any active closed push buttons referring to ground can be used because the MCU used on the radio mod-
ule has internal pull-up resistors on the button input signals. The radio module can handle up to five but-
tons.

Summary of Contents for NRD24V1

Page 1: ...All rights reserved Reproduction in whole or in part is prohibited without the prior written permission of the copyright holder February 2007 Headset Reference Design nRD24V1 User Guide v1 0 ...

Page 2: ...hese products can reasonably be expected to result in personal injury Nordic Semiconductor ASA cus tomers using or selling these products for use in such applications do so at their own risk and agree to fully indemnify Nordic Semiconductor ASA for any damages resulting from such improper use or sale Contact details For your nearest dealer please see http www nordicsemi no Receive available update...

Page 3: ...Jumpers 12 3 2 3 Antenna 12 3 2 4 Power supply 12 3 2 5 Buttons 13 3 2 6 Programming 13 3 3 USB dongle 14 3 3 1 USB Interface 15 3 3 2 Micro controller 15 3 3 3 Radio circuit 15 3 3 4 Power supply 15 3 3 5 Programming 15 3 3 6 Specifications 16 4 Hardware design guidelines 17 4 1 Headset 17 4 1 1 Antenna 17 4 1 2 Interfaces 17 4 1 3 Crystals 18 4 1 4 MCU 18 4 1 5 Battery 18 4 2 USB dongle 19 4 2 1...

Page 4: ...describes the nRD24V1 system HW modules and gives guidelines on how to take this ref erence design and build it into a headset application for a finished product The nRD24V1 consists of a USB dongle and two application boards with a radio module mounted You can establish a full duplex voice link between one application board and the USB dongle or between the two application boards Target applicati...

Page 5: ...guration Figure 1 Headset unit with a USB configuration Figure 2 System diagram of headset unit with USB configuration Figure 3 Headset unit with an audio dongle configuration and Figure 4 System diagram of headset unit with audio dongle configuration illustrate the headset unit with audio dongle configuration Figure 3 Headset unit with an audio dongle configuration USB dongle Headset unit DAC ADC...

Page 6: ... 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 w...

Page 7: ...r FR4 circuit board with components on one side Figure 5 nRD24V1 radio module 3 1 1 Audio Codec The audio codec is a XE3005 from Semtech that receives a 4 096 MHz master clock from the micro con troller The micro controller configures the codec through the SPI interface The 8 ksps audio samples are transferred on the I2S interface where the micro controller is the bus master The microphone input h...

Page 8: ...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...

Page 9: ...ns Operating conditions Status Value Supply voltage 1 9 3 6 V Current consumption Idle 1 mA average 15 mA peak at 2 5 V supply Connected 7 mA average 15 mA peak at 2 5 V supply Radio frequency 2402 2478 MHz Output power 0 dBm PCB attributes Description PCB type 0 8 mm 4 layer FR4 PCB dimension length x width x height 25 mm x 12 mm x 0 8 mm ...

Page 10: ... This module can be used to set up a wireless audio link for example from a PC to a headset The radio module is the same for both sides of the link but needs some external components to interface with either the PC audio connections or a microphone loudspeaker for a headset 1 Radio module 7 P3 external power 2 Linear regulator 8 Batteries 3 Jumpers 9 Switches 7 and 8 4 Audio interface 10 ISP progr...

Page 11: ...e 3 2 1 2 PC interface The differential loudspeaker output from the codec must be connected single ended to the PC microphone input and the PC loudspeaker output must be connected to the codec microphone input to interface with a PC audio port Figure 8 PC input interface shows the networks that accommodate this The loudspeaker output from the PC must be level adjusted and a network as shown in Fig...

Page 12: ... contains a footprint for a CR2 Li battery holder 1 2 AA Bulgin BX0031 Alternatively an external power supply can be connected to P3 You select battery or external voltage with SW6 The voltage supply to the RF module should be between 1 9 and 3 6 V If the onboard 2 5 V linear regula tor is used the input voltage should be between 3 and 15 V The linear regulator can be switched on or bypassed with ...

Page 13: ...ogramming tool like the STK500 from Atmel The programming procedure is as follows 1 If the unit has never been programmed set the AVR fuses Preserve EEPROM memory through chip erase cycle EESAVE 0 Brown out detection level at Vcc 1 8V BODLEVEL 110 Clock output on PORTB0 CKOUT 0 Ext Crystal Osc Frequency 3 0 8 0MHz CKSEL 1101 SUT 11 2 Write the SW hex file into the AVR program memory 3 Write a 3 by...

Page 14: ...d is identified as an audio device in the PC operating system The USB dongle is mounted on a 0 8 mm 4 layer FR4 circuit board with components on both sides of the board Figure 11 nRD24V1 USB dongle top side Figure 12 nRD24V1 USB dongle bottom side 1 MCU 3 nRF24L01 2 MCU crystal 4 RF crystal 1 USB MCU 3 ISP connector 2 EE Prom 1 2 3 4 1 3 2 ...

Page 15: ...samples from the radio circuit to 16 bit linear PCM Handling the RF protocol Optional HID interface for communication with PC application In addition an LED output is available The LED will light up when USB audio activity is present on the USB port 3 3 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 freq...

Page 16: ...ble 5 Physical Specifications Operating conditions Status Value Supply voltage 4 5 5 5 V Current consumption Idle 24 mA Connected 28 mA Radio frequency 2402 2478 MHz Output power 0 dBm PCB attributes Description PCB type 0 8mm 4 layer FR4 PCB dimension length x width x height 42mm x 16mm x 0 8mm ...

Page 17: ...al On this antenna terminal any 50 ohm 2 4GHz antenna can be used from an inexpen sive PCB antenna to space saving chip antennas There are different types of PCB antennas from inverted F antennas to simple quarter wave antennas You must know the characteristics of the chosen antenna and implement it as required Tuning the antenna will be necessary because an antennas impedance and performance is a...

Page 18: ...be external 1kbyte of IRAM can maybe work with 512kbytes 8kbyte program memory possible to get down to 5 to 6kbytes One Double buffered synchronous hardware SPI both on RX and TX or Ideally I2S interface One SPI port for RF and codec Watchdog times for power management One 16 bit timer Master sync clock One 8 bit timer hardware sync clock 1 9 to 3 6V supply voltage 4 1 5 Battery The batteries incl...

Page 19: ... antenna matching network to match the impedance at the antenna s terminal Another important task of the antenna matching network is to suppress spurious energy This can be achieved by following our White Paper named Tuning_the_nFR24xx_matching_network available on our website www nordicsemi no 4 2 2 MCU A replacement of the MCU must fulfill these requirements 8 bit MCU 6 MHz clock frequency 1 to ...

Page 20: ...ation Board PCB1 PCB BC847BL Q1 SM SOT23 NPN BC847BL 470 R3 SM 0603 Resistor 0 1W 0603 1 100k R4 R5 SM 0603 Resistor 0 1W 0603 1 56 R6 R7 SM 0603 Resistor 0 1W 0603 1 0 R8 R9 R12 SM 0603 Resistor 0 1W 0603 1 1k R13 R16 R17 R18 R25 SM 0603 Resistor 0 1W 0603 1 47 R14 SM 0603 Resistor 0 1W 0603 1 220 R15 SM 0603 Resistor 0 1W 0603 1 22k R19 R20 R21 R24 SM 0603 Resistor 0 1W 0603 1 4 7k R22 R23 SM 06...

Page 21: ...M 0402 Inductor RF LQP15MN8N2B02D 5 6n L3 SM 0402 Inductor RF LQP15MN5N6B02D USB A P1 CON USB A PLUG USB connector 48037 2100 nRF24L01 VoIP USB Dongle Board PCB1 PCB PDTC115TU Q1 SM SOT323 NPN with resistors PDTC115TU 22k R1 SM 0402 Resistor 0 1W 0402 1 22 R2 R3 SM 0402 Resistor 0 1W 0402 1 1M R4 SM 0402 Resistor 0 1W 0402 1 100K R5 SM 0402 Resistor 0 1W 0402 1 0 R8 R9 R21 R26 SM 0402 Resistor 0 1...

Page 22: ... 10 1 0n C17 SM 0402 Capacitor 0402 X7R 50V 10 0 8p C18 SM 0402 Capacitor 0402 NP0 50V 5 4 7n L1 SM 0402 Inductor RF LQP15MN4N7B02D 8 2n L2 SM 0402 Inductor RF LQP15MN8N2B02D 4 7n L3 SM 0402 Inductor RF LQP15MN4N7B02D nRF24L01 VoIP RF Module Board PCB1 PCB 10 R1 R3 SM 0402 Resistor 0 1W 0402 1 100k R2 R9 SM 0402 Resistor 0 1W 0402 1 1M R4 SM 0402 Resistor 0 1W 0402 1 390k R5 SM 0402 Resistor 0 1W ...

Page 23: ...Revision 1 0 Page 23 of 25 Headset Reference Design v1 0 5 2 Application board schematics ...

Page 24: ...VoIP RF Module Board R7 DNM R7 DNM R3 10 R3 10 U4 nRF24L01 U4 nRF24L01 ANT1 12 ANT2 13 IREF 16 VDDPA 11 VDD 18 VDD 7 VDD 15 DVDD 19 VSS 14 VSS 20 VSS 17 VSS 8 XC1 10 XC2 9 CE 1 IRQ 6 CSN 2 SCK 3 MOSI 4 MISO 5 CP12 CP12 U3 ATMega88 U3 ATMega88 PD0 RXD 30 PD1 TXD 31 PD2 INT0 32 PD3 INT1 1 PD4 XCK 2 PD5 9 PD6 10 PD7 11 PB0 CLKO 12 PB1 13 PB2 SS 14 PB3 MOSI 15 PB4 MISO 16 PB5 SCK 17 PB6 XTAL1 7 PB7 XT...

Page 25: ...R12 3 3k R12 3 3k L1 2 7n L1 2 7n C6 10n C6 10n L2 8 2n L2 8 2n U2 nRF24L01 U2 nRF24L01 ANT1 12 ANT2 13 IREF 16 VDDPA 11 VDD 18 VDD 7 VDD 15 DVDD 19 VSS 14 VSS 20 VSS 17 VSS 8 XC1 10 XC2 9 CE 1 IRQ 6 CSN 2 SCK 3 MOSI 4 MISO 5 U1 SN11220ACF U1 SN11220ACF VDD 7 TAVDD 9 VDD 21 VSSA_PLLA 23 TAVSS 12 VDDOUT 35 VDD5D 36 VSS 37 VDD 46 VSSA_PLLB 48 XSDIN 24 XSCLK 25 XLRCK 26 XSDO 27 XMCLK 32 GPIO0 20 GPIO...

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