What do I want in my Android Phone?

Big Screen, more RAM, Stock Android or Good Camera - What are my priorities. So here goes a list of items that one should check out and the reasons for doing the same

4.5 inch is about the minimum required today for a decent experience with Social media, emails and light reading. (A 4 inch one is a heavy compromise)
5 Inch is the minimum for people who do a lot of reading online - This is also the ideal size for a compromise between handling ability and readability.
5.5 Inch is the ideal size for reading (most kindle models are 6 inch). But this is a little big for single handed reading.

With the kind of apps being released and the frequent updates, 1 MB is minimum

Some important apps do not work with anything below 4.2 And a few require 4.4 (kitkat) - So I would suggest kitkat at the minimum.
Stock Android is your best bet - Since this is more of a dream, the version that has the minimum bloatware should be ok.
Update: Marshmallow (6.0) is out and it is really good.

I have taken this as a separate sensor. There are some phones which have been sold with A-GPS which did not have a real GPS sensor - DO NOT buy these if you need maps or navigation.
A-GPS is a technology name that provides assistance to the real GPS sensor by providing approximate location information through cellphone towers.  The real GPS sensor then uses this to get the exact co-ordinates much faster than if it did not have the assistance of A-GPS.

At the minimum  - Accelerometer
Preferable to have a Magnetometer (ecompass) - Many apps that show direction or are used for navigation perform better with an ecompass - Personally this is in my required list of sensors.  I have found some apps do not work altogether without the ecompass, like antenna finder apps.
A Gyroscope helps in a faster fix when using the GPS and is useful in somegames as well  - Not absolutely necessary

Bluetooth 4.0
Wifi b/g/n  (minimum b/g)

Solar Thermal

At home we need Hot water for bathing and washing.
Industries require hot water for various processes including space heating and climate control.

Solar Hot water systems are the best choice for domestic as well as industrial use.  They are more efficient when compared with Solar PV in converting the suns energy into useable energy.

A typical Domestic hot water system consists of a Solar Thermal Panel (1, 2, 3 or even 4 panels are used for a single system).  The other important component is the Solar Tank.  This is where hot water is stored.  It is thermally insulated and is the equivalent of a Battery in a PV system.

Although there are two basic types of Panels - Evacuated tube type & Flat Plate type - the Flat Plate Collector is more commonly used.

Each Panel is approximately 2 square Metres.
It generates the equivalent of 5 KWh of electricity on a typical Sunny day in most parts of India.  (The generation will vary by geography & season).
If we compare this with a 2 square metres of Solar PV panel; a PV panel generates about 1 KWh of electricity.

My first 'to be' crowdfunded project

Low Voltage DC Lighting

12V DC & 24V DC LED lights

LED Lights that can work off a Standard Car battery is an attractive proposition.  We have created a few designs on 12V as well as 24V DC.

It is important that LEDs are driven with a constant current.  An LED is a current driven device. That is it will light up to its given intensity when the rated current flows through it.  Its colour rendition will also be specified at that current.

Anything above or below the rated current two things will happen.
  1. The intensity will change, as will be the efficacy i.e. lumens/watt
  2. The Colour temperature will shift and you may not get the white light that you expect.
What is the role of voltage?
Once you ensure a constant current (we will see how we can achieve that later), we can then measure the voltage across the terminals of the LED.  This voltage should be in a range specified by the manufacturer.  For White LEDs it is usually in the range of 2.9 to 3.5 Volts.  Whatever the current you deliver this voltage will remain more or less close to these values.

That is precisely the reason that you should not directly apply a voltage source to an LED.  Let us assume your LED voltage (Called the forward voltage) is 3,2 Volts, and you apply say 13.2 Volts (a normal lead acid battery voltage) to it.  What will happen?
As noted the voltage across the LED terminals cannot increase significantly.  Let us assume it remains at 3.2 volts.

Now 13.2 - 3.2 =10.5 is the voltage that should be dropped somewhere else in the loop.
This is what will be dropped by the internal resistance of the battery.  Since the value of such a resistance is very small the resultant current which is 10.2/R will be huge.  This will burn out the LED.
Of course, this is an extreme case.  However, in reality for even a 4 volts put directly across an LED, excess current will flow through the LED and shorten its life.

Hence: The requirement of a constant current source for the LEDs

Below is a simple circuit which achieves this in a DC circuit.
And here is the board if you want to fabricate this PCB

Rail Stations to be LED lit

Virgin Trains: LED lighting at stations is as much about customer satisfaction as it is about energy

.............Virgin is refraining from installing high levels of intelligent lighting system in which, for example platform lights would remain off when not needed, and turn on when sensors detect people on the platform, because such systems could confuse train drivers........Click the link to read more.