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.
