Optical Mouse

We are back with the Disassemble series. This time with an optical mouse. We will try to figure out how the optical mouse works.

Tools of the trade.

We open up the mouse

and the insides plop out.

The LED that you see in the image below is the source of the red light that you see under the mouse.

The plastic “thingy” has a convex lens that directs the light from the red LED and directs it downwards.

There is another convex lens on the thingy, seen as the round dent in the image below.

The lens gathers the reflected light from the surface on which the mouse is resting. The light goes into a small hole pointed in the image below on the underside of the mouse.

The light goes into the hole which is part of a microchip. The chip is basically a very sensitive signal processor that continuously compares the images sent in through the hole and compares it with the previous images to identify the movement of the mouse.

This LED is just to light up the scroll button. Just above the this LED is the middle button below the scroll wheel.

The red thing pointed is compressed when the left mouse button is pressed.

Scrolling the mouse wheel turns this contraption which in turn translates that into signals that the laptop can understand.

A simple collection of a couple of LEDs, one of which is just for show, and a microchip is what it takes to move that versatile little pointer on your whim.

The Brain Structure

The Brain

As a lay man who knows just a little more than nothing, writing about the most complex organ in a human body is laughable at best. But I do like to make people laugh, so  here goes nothing.
The human brain weighs around 1.5 kg and its volume ranges from 1130 Cm3 in women to 1260 cm3. Thus the age old assertion that men has more brains than woman has some basis in facts. 😀 But this has no implications on the cognitive ability of the two genders.

The brain is divided into two hemispheres, the left and the right. Corpus Callosum is a structure that connects the left hemisphere with the right one. The left hemisphere is generally associated with reasoning and language functions like grammar and vocabulary along with some arithmetic and numerical computations. Right Hemisphere is more artistic in nature with activities like intonation, visual and audio stimuli, spatial and facial perception concentrated there. Various distinct human abilities like speech, language comprehension are concetrated in specific areas of the hemispheres; Broca’s area in the left frontal lobe (mechanics of speech) and Wernicke’s area in the left posterior area (language comprehension). Wada Test is used to test the dominance of hemisphere. More about it later.
The different parts of the brain are as below:

  • Cerebrum
  • Brain Stem
  • Cerebellum

The Cerebrum is the biggest part of the Human Brain and consists of Cerebral Cortex, Basal Ganglia and Limbic System. The cerebrum or the telencephalon can also be divided into lobes viz., Frontal Lobe, Parietal Lobe, Occipital Lobe and Temporal Lobe.

Cerebral Cortex is the outermost part of the cerebrum and it is critical for memory, thought, language, consciousness etc. It is gray in color in preserved brain and hence it is also known as gray matter. The cerebral cortex is folded into fissures or grooves known as Sulci.

Basal Ganglia is situated below the cerebrum and is associated with motor control and learning. It sure looks like a bluetooth headset. Basal Ganglia inhibits various motor systems and removal of these inhibitions results in motion. Injury or degeneration of Basal Ganglia thus results in various motor diseases like Parkinson’s and Huntington’s disease.


Limbic System is also present below the cerebrum and is associated with emotion (I think my limbic system is severely compromised), long term memory (yep it is) and smell.

Frontal Lobe, is the front part of both the hemispheres just behind the forehead and temple. It governs planning, attention, reward etc. Lobotomy or removal of the frontal lobe was a popular psychiatric treatment used in the early parts of the previous century. This was mentioned in Martin Scorsese’ Shutter Island movie. Broca’s area lies in frontal lobe.
Parietal Lobe lies behind the frontal lobe. It plays an important role in managing sensory information from various parts of the body and also manipulation of objects.
Temporal Lobe, below the frontal and the parietal lobe is involved in auditory sensing and long term memory as also language semantics (Wernicke’s area lies in thie lobe).
Occipital Lobe is at the back of my head. Literally. It deals with visual sensation. Why is the visual part of the brain so far away from eyes is beyond my understanding.

Brain Stem is the posterior part of the brain. The sensory and motor connection of the brain passes through the brain stem to the spinal cord and then to the rest of the body. It includes Medulla Oblongata (controls involuntary or autonomous activities like breathing, blood pressure, heart rate etc), pons (Above Medulla and deals with equilibrium – which I think means it controls the inner ear -, taste, eye movement, facial expression and sensation, bladder control (now you know whom to blame when you wet your bed.) etc) and Mesencephalon (I dont know what this thing does)

Cerebellum is lowest and most backward (from the point of view of location) part of the brain. Known popularly as Chota Dimaag, Cerebellum controls motor functions, emotional functions like fear and pleasure and cognitive functions like attention and language.

Spinal cord extends from the Medulla and goes through the spine (The vertebral Column) and acts as the connection from the brain to the body. It also plays an important role in reflex action. Thus the sudden movement that we make – like blinking of eye when something approaches it – is regulated by the spinal cord even before the signal reaches the brain. This is obviously a defense mechanism developed during our days and nights surviving the prehistoric jungles, when the split second time that neural signal takes to travel through the spinal cord to the brain and back was the difference between life and death.

The brain is essentially suspended inside the skull in a fluid called the cerebrospinal fluid. The blood brain barrier protects brain from many types of harmful chemicals and pathogens. In small children the distance between the brain and the skull is even more pronounced. Thus shaking of small babies can result in severe trauma to the brain and may even result in death. This is known as the Shaken Baby Syndrome.

All the images courtesy Wikipedia.

The Repellent

For my first post in the disassemble series I am going to look inside a simple All Out Mosquito Repellent.

The device appears to be working with its light glowing as seen in the below image.

Repellent1

But the device does not work as concluded by all the bite marks on my body and an absence of smell of the liquid. Note that in the image I have removed the bottle that contains the repellent liquid.Repellent2

The underside with the screws.

Opening up the device

Further disassembly

Going even further

So basically the device consists of a pair of aluminium rings separated by insulating material and a resistor. The resistor is color coded probably Red – Violet – Gold/brown – Blue — Which makes it either 2.7 ohms or 270 ohms with a tolerance of +/- 0.25% 🙁 The colors are not very visible. Its more likely to be 270 ohms.

What I dint get is what is that circularish, brownish object between and above the two aluminium rings. I don’t know its function.

Learnings from this experiment:

I need better tools. May be a plier and some other tools. Also some electrical measuring instruments like a multimeter. Also as I progress from electrical to electronic instruments, my knowledge would be woefully inadequate to deal with the complexity.