Ever wondered how your most precious Smart phone’s Touch Screens work, here is the answer to your curiosity.

Touch Screen Technology: How it works

There are three components used in touch screen technology:


The touch sensor is a panel with a touch responsive surface. Systems are built based on different types of sensors: resistive (most common), surface acoustic wave, and capacitive (most smart phones). However, in general sensors have an electrical current running through them and touching the screen causes a voltage change. The voltage change signals the location of the touching.

The controller is the hardware that converts the voltage changes on the sensor into signals the smart phone or other device can receive.

Software tells the smartphone, what’s happening on the sensor and the information coming from the controller. Who’s touching what where; and allows the computer or smart phone to react accordingly.

Resistive Technology:

Offering excellent durability and resolution, resistive technology is used in a variety of applications and environments. A resistive sensor is a transducer or electromechanical device that converts a mechanical change such as displacement into an electrical signal that can be monitored after conditioning with potentiometer for example, being the most basic one. Similarly, analog resistive touch screen is a sensor consisting of two opposing layers, each coated with a transparent resistive material, usually ITO (indium tin oxide). The layers are separated by a pattern of very small transparent insulating dots. Silver ink bus bars make an electrical connection to the surface of the ITO at the outside edges, spanning the desired axis of the given layer. Silver ink traces connect the bus bars to an electromechanical connector used for interfacing to the sensor (screen). The screen has a hard, durable coating on the outer side, and a conductive (ITO) coating on the inner side. When touched, the conductive coating makes electrical contact with the ITO coating on the glass, and a touch is registered by the analog controller. Analog resistive touch screens are available in three types, 4-wire, 5-wire and 8-wire. Resistive touch screen excels at detecting pointed touch points like a standard stylus.

 Capacitive Technology:

Capacitive touchscreens works in quite a different way; instead of relying on user to force the touching of two separate layers of sensors, it works by sensing conductivity — the electricity transferring feature that naturally occurs in water-consisted things, like our human fingers and hence does not require to be pressed forcefully but a smooth touch suffices.

Mutual capacitive sensors have a capacitor at each intersection of each row and each column. A 12-by-16 array, for example, would have 192 independent capacitors. A voltage is applied to the rows or columns. The touchpad contains a two-layer grid of electrodes that are connected to a sophisticated full-custom mixed signal integrated circuit (IC) mounted on the reverse side of the pad. The upper layer contains vertical electrode strips while the lower layer is composed of horizontal electrode strips. The IC measures "Mutual capacitance" from each of the horizontal electrodes to each of the vertical electrodes. A human finger near the intersection of two electrodes modifies the mutual capacitance between them, since a finger has very different dielectric properties than air. When a user touches the screen, some of the charge is transferred to the user, and makes the potential difference on the screen. After the panel controller recognizes that, the controller will send the X-Y axis information to the software. Mutual capacitance allows multi touch operation where multiple fingers, palms or styli can be accurately tracked at the same time.

Self-capacitance sensors can have the same X-Y grid as mutual capacitance sensors, but the columns and rows operate independently. With self-capacitance, current senses the capacitive load of a finger on each column or row. This produces a stronger signal than mutual capacitance sensing, but it is unable to resolve accurately more than one finger, which results in “ghosting”, or misplaced location sensing.

A regular stylus on capacitive screen won’t work, since usually the stylus is made from plastic which doesn’t have a conductive feature, but smart phones like Samsung Galaxy Note having capacitive screen uses a capacitive stylus, which is tipped with some form of conductive material, such as anti-static conductive foam.

Mutual and Self capacitance based screens are Projected capacitive touch (PCT) technology, while the other is Surface Capacitance technology, most often used in simple applications such as industrial controls and kiosks, which I refrain to explain it here.

Ending on a note from end-user point of view:

Owing to the technology mentioned above, for resistive touchscreen the user need to press a bit harder, while on the capacitive touchscreen the user need to press a little longer ;)

It’s hard to imagine that so many events take place in a fraction of second at a simple touch from user.

Have a good day!

Feedback welcome at sandhya.dholani@gmail.com

It is said that history invariably repeats itself. One example that strikes me is that of the BBC Micro Computer. Developed by Acorn Computers in the year 1981, it was a low cost computer to popularize programming and increase computer literacy among students. The specifications were quite good for a computer 20 years back. It had a 20 mb hard drive and 16 kb RAM. 640x256 was the highest supported resolution. Even with a price tag of £235, it was wildly popular at that time and sold 1.5 million units. UK was thus the epicentre of a computing revolution at that time.

Now fast forward the timeline by 30 years: It is 2011 and the UK government realized that their magnificent computing legacy has suffered a lot. Applications for computer science degrees have been dwindling and there is a growing disconnect among the students regarding IT and the things that make it up. Out of 27000 teachers qualifying in 2011 only 3 had a computer science degree. The government realized that the only way to work around this problem was to actively involve school kids in programming. Give them a low cost tool to tinker with and let their imagination do the rest. A non profit Raspberry Pi foundation led the charge to create such a device. They partnered with the University of Cambridge and Broadcom Corporation. The end result was the worlds cheapest computer – the Raspberry Pi.

It is a credit card sized single board computer and boasts of some humble yet pretty impressive specs : ARM11 Processor, 256 mb Hynix RAM, Broadcom GPU (supports 1080p30 graphics), 2 USB ports, HDMI port, 10/100 Ethernet port and a 3.5 mm audio jack. An OS has to be booted via a SD card that has to be purchased separately. Wait, did I tell you the price tag ? A meagre $25 for Model A (1 USB port, no Ethernet port) and $35 for model B (2 USB ports and an Ethernet port). Impressive, eh ? Its performance is roughly equivalent to a Pentium II. Operating systems like Fedora, Archlinux and Debian are supported by default. Android support might come later on. Anticipation for this product has been building up long way before its launch. People on the forum have been discussing creative ways to put this to use. Some of these are using it as a GPS navigator, CNC machine controller, weather balloon, augmented reality, software defined radio. The list is limited only by imagination.

The first batch of these is due to arrive in a month. On Element14 over 1,00,000 orders are pending and even after that 70,000 registrations have been made. So it will be quite a while before I get my hands on it. Popular tech magazine PC Pro gives it an overall rating of 5/6 and says “To create a PC for the price of a round of drinks is nothing short of extraordinary especially given that similar projects like TI Beagleboard, Cubox and Allwinner 10 have failed to reach that level of affordability.” Some folks ported Quake III arena on the R-pi and played a deathmatch which is kinda cool btw ! :)

Contrast this with the situation in our country. The Aakash project has been up for around a year and hasn’t delivered. Datawind just launched Ubislate 7+ and Ubislate 7c which are the commercial counterparts of the Aakash with no word on when students might actually get their hands on the $35 tablet. Initial reviews of the product have been disheartening. As with every other project, this one too had its fair share of controversies.  When one compares the world’s cheapest tablet with the world’s cheapest computer some stark differences come to mind: the Aakash and the Raspberry Pi is the way in which the governments approached the problem of popularizing IT education. While Raspberry Pi is a non profit, Datawind is a commercial entity. Also it pays a lot to actively engage a user community beforehand. The Raspberry Pi Forum is a solid example of that. What do you think? Drop me a line at shahkushan1@gmail.com. I leave you with a TEDx video wherein Eben Upton (the chief designer of Raspberry Pi SoC ) talks about his product. (http://www.youtube.com/watch?v=6xFzVuxldqs)

- Kushan.

Espoo is the second largest town in Finland. This April, Espoo will host the opening of a very popular theme park. The park is all about slingshots, birds and pigs. The park is co-sponsored by Rovio Mobile, the company that created the Angry Birds franchise. Rovio (Finnish for bonfire) raised $42 million in venture capital last year after the disruptive success of Angry Birds. But the ascent to that position was never easy and its growth story is actually an inspiring lesson in patience.

Niklas Hed was fond of making games since he learnt to code in Pascal. On the other hand, Mikael Hed developed a mobile game for a competition at Helsinki University and subsequently won the contest. Niklas founded a small gaming company called Relude in the year 2004 and asked Mikael to become the CEO. Both were initially sceptical of the company lasting long. Mikael’s father invested €1 million in the company and they started subcontracting work for other companies like EA Games and Digital Chocolate. They also developed quite a few games for the Nokia Symbian Platform.

Then the bad times dawned in. Mikael left the company due to certain issues with his father. They realized that since they weren’t really creating content but were third party developers and this was affecting their business a lot. In 2007, the company size reduced from 50 to 12. The company was close to bankruptcy. Something had to be done and quickly.

Mikael was called back. Coincidentally this was the time of the rise of the Apple App Store. This meant that even smaller companies like Rovio could feature apps on the store. They decided to use this to their advantage. They would continue to work for hire and develop iPhone games in their slack time. Success on the iPhone platform would open up many other arenas as well : Android, PC…

In March 2009,  their principal game designer came up with the idea of birds that were angry, had no feet and couldn’t even fly. They had no special abilities at first. Just some birds, a few coloured blocks and the objective was to use the birds to destroy the blocks. The pigs were added later on. The team then came up with the story of the pigs stealing the birds’ eggs as a justification for the birds’ anger. The game didn’t perform well on the App Store at first.

Rovio then decided to tap the smaller markets at first. Thus they started conquering the world one country after another. Starting with their home Finland, it moved on Sweden, Czech Republic, Greece and finally Angry birds got people hooked in US and UK. These two countries now constitute 90% of the total market. It became number one on the App Store. This was followed by the Android and the PC version. Rio and Seasons followed. It has now been played by over 75 million people and it’s the number one App in 68 countries. The trailer of the movie Rio racked up 500,000 views in a week. Sales of toys aside the Angry Birds brand now generates a revenue of €50 million. All this success did not come overnight. Angry birds was Rovio’s 52nd game. That’s right, it took 6 years and 51 games for Rovio to find the correct formula. Success indeed comes to those who persevere. How many of us start an endeavor with a lot of energy and then leave it halfway through in the face of challenges ? Had the Heds done that we wouldn’t be playing Angry Birds Space right now, which btw is awesome. Kudos to Rovio ! :)

- Kushan.

Modern Marvels : Dropbox

Dropbox is a file sharing service founded by MIT grad students Drew Houston and Arash Ferdowsi who used to forget USB drives at work. What they did at that time was to email files to themselves in order to access them from different computers. (Until I heard about Dropbox, I used to do the same too.) Basically their vision was to develop a solution to this problem.


There are a couple of things I love about Dropbox :

It is ridiculously simple to use and the makers are bent on making it more user-friendly with each new feature they roll out. Apart from the 500 mb I earn with each referral, the fact that it is free makes it awesome too. Another cool feature is Revision Control wherein I can restore a previous version of an accidentally changed file. Even deleted files can be restored.

There are a lot of cool things one could do with Dropbox including hosting an entire website on it or else using it to stream your home music collection.

Steve Jobs was so impressed with Dropbox that he called Drew Houston and offered to buy the company so that he could merge Dropbox with iCloud. Drew Houston refused him in the face and said he had his own vision of the company. It takes guts to stand up to Steve Jobs. And here is a lesson for youngsters like us.

I was initially apprehensive that it would hog my dialup connection but I have been using it since some time now without any glitches to normal browsing.

Two of my project partners and me used Dropbox to work on the same copy of our project report last semester. Each of us was working on a different chapter but when the three of us were done with our work the report was magically complete. The sum of all parts. All due to Dropbox’s seamless sync feature.

Achieving this level of simplicity of use across all the major Operating Systems (Lion, Leopard, Windows, Linux, Android), four Browsers (Chrome, Firefox, IE, Safari) and all the network file systems (EXT, NTFS) is a marvellous feat in itself. Drew Houston says that he and his partner spent a major part of their 20s working out the incompatibilities between all these platforms. Just imagine the amount of thought process that must have gone behind each and every feature. 

I love the site UI and its graphics too. This particular one (listed on the Jobs page of the site) stands out. 


Dropbox stores all our files on an Amazon S3 Server bucket. It might actually have various backups distributed over multiple buckets around the world. IMO, it utilizes rsync algorithm or a variant to sync our files across different locations. Rsync is an open source algorithm developed by an Australian students Andrew Tridgell and Paul Mackerras. Here’s how it works:

The problem

Imagine you have two filesA and B, and you wish to update B to be the same as A. The obvious method is to copy A onto B.

Now imagine that the two files are on machines connected by a slow communications link, for example a dial up IP link. If A is large, copying A onto B will be slow. To make it faster you could compress A before sending it, but that will usually only gain a factor of 2 to 4.

Now assume that A and B are quite similar, perhaps both derived from the same original file. To really speed things up you would need to take advantage of this similarity. A common method is to send just the differencesbetween A and B down the link and then use this list of differences to reconstruct the file.

The problem is that the normal methods for creating a set of differences between two files rely on being able to read both files. Thus they require that both files are available beforehand at one end of the link. If they are not both available on the same machine, these algorithms cannot be used (once you had copied the file over, you wouldn’t need the differences). This is the problem that rsync addresses.

The rsync algorithm efficiently computes which parts of a source file match some part of an existing destination file. These parts need not be sent across the link; all that is needed is a reference to the part of the destination file. Only parts of the source file which are not matched in this way need to be sent verbatim. The receiver can then construct a copy of the source file using the references to parts of the existing destination file and the verbatim material.

Trivially, the data sent to the receiver can be compressed using any of a range of common compression algorithms, for further speed improvements.

Suppose we have two general purpose computers α and β. Computer α has access to a file A and β has access to file B, where A and B are “similar”. There is a slow communications link between α and β.

The rsync algorithm consists of the following steps:

β splits the file B into a series of non-overlapping fixed-sized blocks of size S bytes. The last block may be shorter than S bytes.

For each of these blocks β calculates two checksums: a weak “rolling” 32-bit checksum and a strong 128-bit MD4 checksum.

β sends these checksums to α.

α searches through A to find all blocks of length S bytes (at any offset, not just multiples of S) that have the same weak and strong checksum as one of the blocks of B. This can be done in a single pass very quickly.

α sends β a sequence of instructions for constructing a copy of A. Each instruction is either a reference to a block of B, or literal data. Literal data is sent only for those sections of A which did not match any of the blocks of B.

The end result is that β gets a copy of A, but only the pieces of A that are not found in B (plus a small amount of data for checksums and block indexes) are sent over the link. The algorithm also only requires one round trip, which minimises the impact of the link latency.

Apart from rsync, Dropbox also utilizes a Watch module on each file to see whether the user has updated it or not.

Our data is now as important as any organ of the body. We feel crippled when we are unable to access it. Fast, Ubiquitous access to data is the need of the hour. Dropbox has actually made this a reality. Although, Google Drive is here and looks a lot like Dropbox, I shall stay with Dropbox for the time being. Cheers !

Posted by Sandhya Dholani..Feedback welcome at sandhya.dholani@gmail.com

What really got me thinking at first was this :

Is there a dearth of Logo Designers in our country ?

Then out of sheer curiosity, i found this. This is the current UI of Amazon : 

And then this : 

Infibeam recently changed its logo, thankfully. 

Indian eCommerce is an awesome (> $10 billion) industry and these companies are certainly well established players. I do not have a clue regarding website design or tried and tested techniques to woo customers but the fact that each of these sites have UI and business models both ‘inspired’ from Amazon speaks volumes.

PS : Infibeam and Flipkart have been founded by ex Amazon employees.

There is certainly no scarcity of creative people in our country but then why do we see such examples among us ? 

Infibeam recently started a service called http://buildabazaar.com/ that enables small stores to establish an online retail presence. I can certainly see that there is a huge market for these kind of services. +1 to Infibeam for that. 

- Kushan.

Initially designed with the motives of connecting the PC to the mobile phone and expanding the number of ports on a PC, USB has become a ubiquitous technology one that we can’t part with. USB was the first true plug and play protocol. It is difficult to come across a device with no USB support at all. Universal Serial Bus was invented by Intel Fellow Ajay Bhatt, an alumnus of M S University Vadodara.


There are basically 3 types of devices in a USB topology.

USB Host : In majority of the cases, the host PC is the USB host. There can be only one USB host. The host initiates all data transfers.

USB devices: Again these are of two types : A hub is used to provide additional attachment points to the USB while the other kinds of devices include cameras, joysticks, mouse, keyboard etc.

A USB cable consists of four wires. Two of them are used to transfer power whereas the remaining two are used to transfer data.

USB supports two data rates :

High speed USB operates at 12 Mbps whereas Low speed USB (1.5 Mbps) is used mainly for low bandwidth devices such as mice. Flooding a low bandwidth device with a high data rate would degrade bus utilization. The Data travels on a differential line (D+ and D-) wherein the clock information is embedded within the data itself. The clock encoding scheme used is NRZI (Non Return to Zero Inverted).

Bus Protocol

All bus transactions involve the transmission of up to three packets. the Host Controller, on a scheduled basis, sends a USB packet describing the type and direction of transaction, the USB device address, and endpoint number. This packet is referred to as the “token packet.”

The USB device that is addressed selects itself by decoding the appropriate address fields. In a given transaction, data is transferred either from the host to a device or from a device to the host. The direction of data transfer is specified in the token packet. The source of the transaction then sends a data packet or indicates it has no data to transfer. The destination, in general, responds with a handshake packet indicating whether the transfer was successful.

Error Correction

It is also important to check the packets for data corruption hence the protocol also includes separate CRCs (Cyclic Redundancy Checks) for control and data fields of each packet. The CRC gives 100% coverage on single- and double-bit errors. A failed CRC is considered to indicate a corrupted packet.

The following data transfers are supported by USB

Bulk data consists of larger amounts of data, such as that used for printers or scanners.

Interrupt data consists of event notification, characters, or coordinates that are organized as one or more bytes. An example of interrupt data is the coordinates from a pointing device. Although an explicit timing rate is not required, interactive data may have response time bounds that the USB must support.

Isochronous data must be delivered at the rate received to maintain its timing. A typical example of isochronous data is video. If the delivery rate of these data streams is not maintained, drop-outs in the data stream will occur and we might miss some video frames in between.

There is a lot of truth in the axiom : Life is too short to eject pen drive safely. Or is it ?

Why computers want you to safely remove USB drives ?

By default, most Operating systems use a technique called Write Caching to optimize USB performance. Meaning, while we transfer files between a PC and another device, lets say a flash drive it will wait for a certain amount of time until it has a lot of requests to fulfill (thus caching these requests) and then completes all those requests together. So even if you see the File copy dialog box now closed to indicate completion, the OS might be actually serving the cached requests in the background. Yanking out a flash drive at this moment will definitely corrupt your data. The Safe remove option flushes the write cache so that the drive can be ejected safely. Windows 7 disables the Write Cache by default. (Device Manager > Disk Drives > Right Click > Properties > Policies) However this isn’t the case if you are using Linux/Mac/an earlier version of Windows.

-Kushan. Feedback welcome at shahkushan1@gmail.com