FRDM KL25Z board-Getting started

The FRDM KL25Z is the board manufactured by "Freescale Semiconductors".FRDM stand for Freedom. KL25Z is "Kinetis L series".The board is powered by ARM Cortex M0+ based processors.

FRDM KL25Z board

                                       

Arduino Uno board

The board is superb!. I've been using this board for almost an year now and trust me..it will not disappoint you.Some of it's best features is it's low cost,outstanding energy effeciency and its processing capability.This board is ideal for anyone wanting to start off with ARM based microcontrollers. Another benefit is that they are Arduino compatible. So any shield that you have for Arduino can be directly plugged into the FRDM KL25Z board and it'll work.

You can purchase this board at a local electronic dealer or you can search for it online at any of the big electronic supplies retailer.The are priced roughly the same as Arduino Uno boards.
The board can be programmed using mbed or Codewarrior IDE.

mbed is an online compiler.So make sure your internet connectivity is decent and if you want to,you can export your program/s to any of the offline compilers as Keil uVision or Eclipse IDEs.
Codewarrior however is offline and is best suited for me.The software is not small to download however.
Recommendation:
1.  PC/Laptop should be ideally with RAM of 4GB,
2.  Hard disk free space: 4GB (after Code warrior IDE installed),
3.  USB data communication permission.

The software download link is
 (NOTE: it is about 1.4GB in size)

http://www.freescale.com/webapp/sps/site/prod_summary.jsp?code=CW-SUITE-SPECIAL&nodeId=0152102726E4D3&fpsp=1&tab=Design_Tools_Tab.

There is a Special Edition by FREESCALE: CodeWarrior for Microcontrollers 10.6 (Eclipse, Offline) (REV 10.6).  You can find this at the bottom most selections options.  Click on this offline software to get downloaded.

IMPORTANT: DON'T FORGET TO CHECK THE "kinetis" DURING INSTALLATION.

                                                            

See you soon on my next post where we will get started with programming this board.

Building the coolest cell phone charger

A lot of my friends ask me "Dude Hari,from where do you get the money to build your projects?".
Well I get 1000 rupees(around $12 American) a month as pocket money for teaching Math and Chess to my two nephews studying in grade 4 and 5 at Mickleover Primary School, Derby, UK.
I know it's not a lot and given the fact as a college going student, I will not be able to save more than 400 rupees(around 6$ American) a month.
So there is limited budget for my projects.

For this reason all of the projects I design and build,I make sure that it is as efficient as possible; most of the times drawing and redrawing multiple circuits and seeing whether I can reduce parts or complexity or sometimes come up with a better design.
Another area in which I save money is that I don't get necessarily build a PCB layout and get the PCB fabricated after completing each project as they are expensive (to me),instead I manually solder them onto the perf-board.

I live at a place called Chunchugatta, a village 2 km off Kanakapura road, Bangalore,India.
We are prone to very frequent power cuts,and they sometimes extend to 3-4 hours.
If at all they supply power,instead of 3-phase it's lousy 1-phase which can be used for absolutely nothing apart from lights or fan I tell you.
On November 6th,it was a horrible 9 hours;from 11:00 to 20:00. Every time a person from the Electricity Department picks the phone,he replies "the lineman has gone for tea.." or "the lineman has gone for smoking..".

This project is built keeping in mind that if in case of a power cut, we can at least charge our phones,for basic communication establishment.
You might suggest a power bank but in my case,if the power bank runs out of juice, ill have trouble charging it.
So a battery powered charger is the only go.

Here is the list of parts and their price:

1. 9 volt battery(1 nos.) or 1.5 volt AA(6 nos.)   --------  as per MRP(mine was 15 rupees)
2. 7805 voltage regulator(1 nos.)                         --------  5 rupees
3. 10uF electrolytic capacitor (2 nos.)                 --------  5 rupees
4. On/Off switch(1 nos.)                                      --------  2 rupees
5. Resistor (330 ohms, 1nos.)                              --------- 1 rupee (its actually 15 paise)
6. LED(any color,1 nos.)                                     ---------  1 rupee
7. Potentiometer(0-100K, 1nos.)                         ---------  7 rupees
8. USB type A female connector(1 nos.)            ----------  20 rupees
9. 9 volt clip(1 nos.) or alligator clip(2 nos.)      ----------  5 rupee
10. connecting wires                                           ----------  as per MRP
11. solder board(small,1 nos.)                            ----------- 5 rupees
12. soldering equipment                                     -----------  well its your choice

The total amount of all the parts are 66 rupees(exactly 1$!!).

The device's ratings:

If you notice carefully on you charger,it will be mentioned
INPUT: (supply input of your country,mine's 240V)
OUTPUT: 5V DC  550mA

So basically the phone will only charge if minimum 5V is applied across the terminals of its battery,and a minimum of 550mA be supplied for it to charge quick and efficient.
Lesser current=>slower charging
Higher current=>fast charging
Very high current=>phone will blow up soon (be cautious of this case)

Before building.

The circuit is:

Design 1 doesn't work.
Go for design 2.
For safety of phone turn "pot" to minimum resistance but not 0 ohms
                                                                                                                                                                                           
   

                                                                                                                                                                                           




What's the "Pot" used for?

Well the Pot is short for potentiometer.It basically is a variable resistor.The more I turn the knob to the right,the greater is the resistance offered and the more the knob turned to the left,the lesser is the resistance.
Lesser resistance=>higher current flows through
Greater resistance=>lesser current flows through

In this case,
1.) if the pot is resisting low,then more current flows through it=>less current flows to the phone=>slow charging=>device is safe

2.) if the pot is resisting high,then less current flows through it=>more current flows to the phone=>more charging=>device is a little unsafe

Time to build.

Well since I had all the parts it took me 1.5 to 2 hours to build it.
(I'm very slow when it comes to soldering!!).
If you need to source out the parts,then it will probably take half a day..


How its turned out:


                                                       

The device in action:

                                      


                                         

How am I improving it?

Well the 7805 converts any input voltage in the range of 7 to 25 volts to 5 volts.In this case I'm inputting an 9 volts but as power is consumed,voltage drops to less than 6 volts.In this case the 7805 is pretty much useless as it wont work for input voltage less than 6 volts.

How do I know the voltage has dropped to less than 6 volts?

Well you see that I have added a LED along a resistor to the output and gnd.
If this LED doesn't glow with a sufficient intensity or doesn't glow at all,i know that the voltage has dropped.

In turn I'm planning to divert the remaining power to a series of power LED's so that it can also function as a torch..a bright one too!!

Any problems?

Well the one problem is that the 9V battery is not capable of supplying 550mA(=0.5A=half an amp!!) of current.
Yes you might mention that if I turn the Pot to 0 ohms,then infinite current will pass through to the phone,but you are missing the point that the phone too offers a resistance and the current will not be able to reach that high a value.

The Solution.

Instead of the 9V, use 6 AA's in series.
Or better yet,use two 9V batteries in parallel.This way,voltage remains same but current supplied doubles.

You can also search for high voltage and current rated re-chargeable batteries online for making use in this project.

Field testing.

 I found that my phone took a long time to charge.
At first I thought that my battery was not supplying sufficient current.
So I rigged up this circuit(well all I did was change the battery to a more powerful one.)
This new power pack is rated at 7V, 2000mAh.
That's a wonderful amount of power that it's supplying.

Even with this new circuit,the charging time didn't improve considerably.
On closer inspection I found that most power banks provide a 5V,1A or a 5V,2.1A output.
My circuit was giving 5V alright but the current supplied is nowhere close to 550mA.
So here comes the bug.
The phone too offers a resistance and that resistance is greater than 100K ohms.
Effectively majority of the current passed through the pot instead of going to the phone.

Solution.

Try adding more resistances in series to the pot, the greater the resistance added, the better off you are.
You're ultimate goal should be to increase the total resistance to greater than that of you're phone, so that a good amount of current can be supplied to charge the phone.

If you are a daredevil, I would suggest you to remove the pot and instead directly power the device.This ensures that max current is supplied to the phone.
Do this at your own risk though.

 Quick Tip.

1. If you want higher voltage, connect batteries in series.

2. If you want higher current,connect batteries in parallel.

3. If you want higher resistance, connect resistors in series.
    Effective resistance will be greater than the value of the greatest resistor used.

4. If you want lesser resistance, connect resistors in parallel.
    Effective resistance will be lesser than the value of the lowest resistor used.


See you soon on my next post.
Until then, happy building.