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.
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 Logitech M570 mouse
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.
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.
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.
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.
The Avago lens from the mouse
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.
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.
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.
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.
Today many mice contain scroll wheels. In order to detect the rotation of the wheel, an encoder will most likely be used.
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.
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.
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.
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.
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.
Thanks for reading this week's Teardown Tuesday! Stop by next Tuesday for another teardown.
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