Teardown Tuesday: Wireless Mice! - LEKULE BLOG


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Thursday, 7 July 2016

Teardown Tuesday: Wireless Mice!

Wireless mice were once a luxury item, but are now commonplace. What's inside of them?

In this teardown, we are going to look at two mice and see how what makes them work! This article features a discontinued Lingdu 520 Mouse and a Logitech M570 trackball.
The Lingdu 520 is a typical optical wireless mouse with a scroll wheel. This mouse connects to a computer through an included wireless dongle and is powered by two AAA batteries.

Wireless Optical Mouse
The Lingdu 520 mouse

The Logitech M570 is a wireless trackball mouse that also has a scroll wheel. This mouse connects to a computer through an included unifying dongle and is powered by a single AA battery.

The M570 Mouse
The Logitech M570 mouse

Optical Element

Today most mice work by using a tiny low-resolution video camera to capture repeated images of the surface the mouse is located on. Multiple images of the surface are captured per second in order to calculate speed and direction of motion. In many mice today,  a lot of the image processing and image capturing is handled by special-purpose image processing chips.

Lingdu 520

ADNS-5090 Optical Mouse Sensor
The ADNS-5090 optical mouse sensor

The optical sensor in the mouse is in an 8 pin through-hole package. This sensor is manufactured by Avago Technologies, part number ADNS-5090. This sensor is designed for low-power application and has built-in power saving modes. Inside of this IC, there is a 19x19 pixel image array, hardware to perform signal processing on the data, an LED driver, and a serial port to output the data.

Logitech M570

Logitech m570 sensor
The optical sensor assembly from the M570 mouse

The optical sensor in the Logitech mouse didn't have any part numbers or manufacturer's marks. The imaging array is located in the top coned-shaped extrusion in the module. The module is removable and connects to the main board of the mouse through a removable connector.

Lens and Light

In order to capture the best quality images, optical mice will use illumination such as an LED or laser diode. The light is transmitted to the surface through a lens. In addition to the lens for the illumination, there is often also a lens for the optical sensor.

Lingdu 520

The led in an optical mouse
The LED and lens in the Lingdu mouse

This mouse uses a red 5mm LED light that is mounted parallel to the PCB. The LED is aimed towards a lens assembly that also contains the macro lens for the optical element. This lens is also manufactured by Avago, part number ADNS-5110-001.

Optical Mouse Lens AVAGO
The Avago lens from the mouse

Logitech M570

Mouse Laser Wireless
The optical and image assembly in the M570

This Logitech mouse uses an IR laser to illuminate the surface of the trackball. The laser aperture is visible towards the bottom of the optical assembly. As mentioned before, the laser and optical sensor are in the same package.

RF Module

The key component to any wireless mouse is an RF module. The modules in most wireless mice operate on 2.4Ghz. The range of wireless mice typically isn’t super long, so low-power consumption is often a larger concern. Paired to the RF module is a trace antenna. This type of antenna is used to reduce BOM costs.

Lingdu 520

The RF Transceiver in a wireless mouse
The RF transceiver and antenna in the Lingdu mouse

Due to the chip-on-board design, it is difficult to see exactly what RF module is used. The RF transceiver is located under the black blob of epoxy. The mouse was sold indicating a 2.4GHz wireless connection. Coming out of the transceiver is a trace antenna. On the circuit board, L2 and CF1 tune the antenna.

Logitech M570

Logitech RF Transceiver
The Nordic transceiver and trace antenna on the M570

The Logitech M570 uses a Nordic Semiconductor nRF24L01 single chip transceiver. This transceiver is mounted to the bottom of the mouse’s PCB. Paired to this IC is a trace antenna and passive components to provide impedance matching.

Scroll Wheels!

Today many mice contain scroll wheels. In order to detect the rotation of the wheel, an encoder will most likely be used.

Lingdu 520

lingdu wireless mouse_encoder
The encoder used on the Lingdu scroll wheel 

The Lingdu mouse uses a mechanical encoder to detect rotation and has 25 mechanical steps per revolution. The encoder is in a right-angle through-hole package that the hexagonal shaft of the scroll wheel fits into. The encoder has detents built into it.

Logitech M570

logitech wireless mouse encoder
Components of the optical encoder used in the Logitech mouse

The Logitech mouse uses an optical encoder. The optical encoder consists of an IR transmitter, receiver, and perforated rotating disk that is built into the scroll wheel. In the image above, the blue IR emitter (LD1) can be seen on the right and the IR receiver (LQ1) can be seen on the left.

USB Dongle

Many wireless mice today used their own property RF protocols as opposed to Bluetooth. Wireless mice will often come with a dongle in order to receive the data from the mouse.

Lingdu 520

The Lingdu Dongle
Inside of the Lingdu dongle

Just like in the Lingdu mouse, most of the interesting active electronics are covered by epoxy; the same trend continues in the dongle. The trace antenna in the receiver is visible.

Logitech M570

Inside of the Logitech Unifying Dongle
Inside of the Logitech unifying dongle

The Logitech dongle the is a little more interesting than the Lingdu receiver! Located in the dongle is a Texas Instruments CC2544 2.4GHz system on a chip. This IC features an 8051 Microcontroller core and 2.4GHz transceiver.

Wrapping it up

This teardown shows two different approaches to wireless mice. Although they perform the same function, their construction methods vary greatly. 
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