Design of multi-functional wireless presenters made easy

Wireless presenters have become a powerful tool for professionals to make impressive and effective presentations. They allow presenters to stay mobile and while keeping the audience to follow along flawlessly without unnecessary ‘Next’ and ‘Skip’ kind of instructions to the slide changer. However, just a simple wireless presenter will not be enough to achieve this all. Certain additional features will make it more attractive and useful.

    * Sharp and bright laser pointer to help keep the audience on track visually
    * Built-in, non-volatile storage to allow presenters to carry their presentations wherever they travel
    * Air Mouse functionality enables more complex option menus for managing presentations on the go
    * Form factor which fits comfortably in the hand
    * Low power consumption to make it all the way through long presentations
    * Low cost to keep the wireless present affordable.

Current architectures
Almost all wireless presenters today use the 2.4-GHz frequency band. The design discussed in this article also uses that band. There are two primary components for these kinds of designs: a transmitter and receiver. The transmitter is the wireless presenter tool itself to be held by the presenter to control the presentation remotely. The receiver is typically a dongle plugged into the USB port of the PC where the presentations are stored.

The traditional architecture requires:

    * MCU as the central controller of the design
    * Digital Accelerometer which provides a frequency output or an I2C/SMBus output to support air mouse functionality
    * Wireless RF chipset which can transmit and receive data in the 2.4GHz frequency band
    * Laser device to implement laser pointer functionality
    * Mechanical switches in the wireless presenter for user input
    * Optional LCD Display to provide a better user interface.

The microcontroller serves the role of scanning the buttons for user input, reading the accelerometer, driving the LCD Display, and transmitting read data wirelessly.


There are some major design challenges in this kind of design.  First, a compact form factor is a key requirement for a wireless presenter. As a result, PCB design becomes increasingly more complex as the number of discrete components rises.  Secondly, the system must be power efficient to increase battery life.

Accessing the digital accelerometers also introduces challenges since they provide a pulse width modulated output. The cost of a digital accelerometer is more than a basic analog accelerometer because of additional analog-to-digital circuitry.  In addition, this type of accelerometer requires an accurate timing resource on the microcontroller to calculate the duty cycle. The microcontroller will be occupied calculating the duty cycle of the accelerometer and hence there may be insufficient resources to manage other activities like driving the RF, LCD Display, switch scanning, and so on.

The receiver


The receiver pictured above is designed around a 2-port USB hub. One of the ports is connected to a SD/MMC card controller. The other port is connected to the USB controller, which drives the wireless RF chip. The silicon real estate is more for this kind of a receiver design and hence makes the design complex and larger in form factor. This kind of design also results in increased power consumption, increased system cost, and reduced system performance. USB certification also places some power constraints on the design. Because of the increased power consumption of the system, it might not be able to pass certification testing.
Modified bridging architecture

To overcome the above design challenges, an intelligent bridging design can be used. integrated SoCs such as the Cypress PRoC device combine wireless functionality (WirelessUSB in this case) with a mixed-signal array that enables programmable hardware acceleration. Mixed-signal arrays allow the use of analog accelerometers instead of more costly digital accelerometers, as well as supports control of the laser pointer, switch scanning, driving the LCD, and other extra features.

Integrated SoCs are designed specifically for highly integrated, space-saving, low-cost, wireless systems. Built-in radio capabilities saves board space and helps in achieving a compact form factor wireless presenter. Additionally, integrated radios can include advanced signal technology, such as direct sequence spread spectrum (DSSS) interference immunity technology, which enables a complete wireless subsystem on a single chip.


The lower power consumption of an integrated controller/radio also improves battery life. Design tool suites – complete with compiler, user modules, and assembler – eases the software design process by facilitating hardware/software design. For example, the proprietary KISSBIND protocol allows the transmitter to bind automatically with the provided receiver pair and hence avoid unnecessary confusions because of cross binding. Efficient antenna design allows the transmitter to work from long distances of up to 50 m.


The use of a modified west-bridge architecture provides simultaneous links to independent multimedia and hence eliminates the need for a USB hub. For example, two storage ports across the west bridge Astoria can be configured as per the application design requirement with Port S1 connected to SD/MC/eMMC/eSD non-volatile memory and Port S2 connected to the WirelessUSB radio subsystem across and SPI interface. Note that the designer can choose between embedded or removable storage based on the particular application requirements.

A west bridge architecture also enables the system to interface with standard USB drivers available with Windows and hence eliminates the need for driver development. The device enumerates as a composite device supporting three device classes, namely mass storage for storage, HID1 for presenter functionality, and HID2 for air mouse functionality. The multitasking capabilities of bridge architecture allow use of all three-device functions simultaneously, resulting in better system performance. The smaller footprint of a west bridge architecture helps maintain a compact form factor design. Low power consumption helps to pass the USB certifications without any problems.

About the Authors:
Rama Sai Krishna. V holds an M.Tech in Systems and Control Engineering from IIT Bombay, India. He is currently working as an applications engineer on Cypress USB 2.0 peripherals.

Praveen Kumar.M holds a B.E. in Electronics & Communications Engineering from the College of Engineering, Guindy, Anna University, India. He is currently working as a Sr. Applications engineer at Cypress.