There are a couple ways to tact the problem of battery drain in smart phones. The first is to carry a spare battery around with you. The problem with that is the batteries are expensive, if the contacts touch metal you will start a fire. Also once you’ve discharged both batteries, its back to the battery charger in the car or home to charge two batteries now. Oh and to charge the extra battery you need to put it in the phone, which mean twice as long on the charger.

I recently seen a solar charger for the cell phones, the problem with that is the phone needs to be in the sunlight which also means the extreme heat from the sun. The Incredible suffers from heat charging where if the battery gets too hot it will stop charging and trip the phone out. I overheated my phone a few times while I was travelling in the heat. The Incredible will flash green and orange while on charge to signal overheating.

The last option I seen in an airport is called “The Charging Station”. It is a booth with every adapter known to man and a credit card slot. You buy time to charge your phone; the problem is you need to be tied down to the charging station while it’s being charged.

I knew that I would be using my phone a lot on the last trip I went on, so I wanted to make sure it wouldn’t go dead on my journey. My plan was to make my own Minty Boost from spare parts in my office. A Minty Boost is a small device that uses “AA” batteries and a step up converter, to step the voltage up from 3 volts to 5 volts.

About the Circuit

My plan was to step the voltage down from a 9 volt battery to 5 volts using a 7805 voltage regulator. Two 100uf electrolytic capacitors are used to buffer the voltage for any line noise. They are placed in front of the 7805 and in back. These capacitors are not “required” for use with a 9 volt battery since there is no noise (transformer) that would come from the battery itself. This circuit can be adapted for an old DC transformer so I left them in the schematic. The ceramic 100nf cap is to buffer the voltage during load changes and should be kept in to provide a smooth 5 volt supply.

Construction

I didn’t do anything fancy like etching a PCB, I just used some fabrication board and soldered the leads together. I also took apart an old USB hub and desoldered the female USB A-type connector. The USB connector fit nice on the fabrication perf board. I did use some epoxy to firm it up against the 7805, which worked out well because it acted like a heat sink. Of course I packaged the whole thing in an Altoids mint container that I had lying around. I used double stick tape to mount the board in the mint container and used a Dremel to cut the opening square.

Now anytime I’m out and need a quick charge as long as I have the box in my bag, I can always find a 9 volt and charge my iPod or Incredible back up. During the trip I used it with great success and got an average of two full charges out of a 9 volt battery.

Usually I have a plenty of the cables on hand, but I could not find one of these in my box of tricks. I did have the EIA/TIA Serial to RJ-45 adapter, so I just needed the cable. The cable that comes supplied with Cisco equipment is a flat 8 wire telephone cable with two RJ-45 ends. The cable is called a rollover cable because Pin 1 is connected to Pin 8 on the other end and Pin 2 is connected to Pin 7 on the other end. It’ that simple!

It is sometimes called a null modem cable, because the all of the pins are reversed from side to side. The transmit is rolled over to the receive, the Ready To Send or RTS is directly connected to the Clear To Send or CTS, the Data Terminal Ready DTR is connected to the Data Set Ready or DSR, etc… All of the grounds are commonly tied together as well. This is why connecting to a Cisco device requires 9600 baud, 8 bits, No parity, 1 stop bit and no flow control. This is sometimes referred to as 9600,8,N,1.

The diagram below is how to make the rollover cable from simple Cat5 cable if you do not have the 8 wire flat Telco cable on hand that is usually gray in color. Simple crimp them down on each end of the cable as per the diagram. It does not matter which end is connected to the equipment and which end is connected to the EIA/TIA DB-9 RJ-45 connector.

So I got home that Sunday and my son and I put the Mini-POV3 kit together, it took all of 30 minutes. It is a persistence of view kit, so when you wave the device it spells a word or words out. This concept unfortunately is not something that a 4 year old can grasp and he is like “Wow, what else does it do?”

The heart of the kit is an Atmel AVR ATtiny2313 8-bit RISC Microcontroller; it has programmable inputs and outputs, 2KB of flash memory and can be programmed in-system. The design was ahead of its time and AVR stands for the two designers’ names “Alf and Vegard’s Risc”. The kit also comes with a 9-pin Serial connector. So a couple of tasks to program this thing…

1. Build the project (takes about 30 minutes).
2. Get a straight thru serial cable or directly plug it into the serial port.
3. Download WinAVR from http://www.sourceforge.net/
4. Download Bascom-AVR Demo from http://www.mcselec.com/
5. Learn some QBasic and the inner workings of the Atmel AVR.

Install the WinAVR program, this program will allow you to program the in-system Microcontroller. When you install it: change the path to “c:\WinAVR” and make sure that it puts the AVR binaries in the global path variable; you will be prompted during the install. Now we need to install the Bascom-AVR program which is the IDE or Integrated Development Environment and the Bascom BASIC to machine code complier. To install the Bascom-AVR program accept all defaults during the install, we will set it up next…

Inside of the Bascom-AVR program click on the ‘Options’ menu item and select ‘Programmer’. This is where we setup the tie between the WinAVR program called AVRDude.exe and the Bascom IDE for one click programming. Although you always have the option to find the BIN file and flash it via command line. Click the pull-down menu for Programmer and select ‘External programmer’ now in the tab below called ‘Other’ set the ‘Program’ to the path of the avrdude.exe; so it should look like this “C:\WinAVR\bin\avrdude.exe”. In the ‘Parameter’ field put “-p t2313 -P com1 -c dasa -U flash:w:{FILE}:a”; which tells avrdude.exe to write to a tiny2313, via comport 1, using direct access (dasa) and write to flash, substitute {FILE} for the filename and program it automatically. You can always Google ‘avrdude man’ for the manual page for the avrdude program or just type mine in.

Now let’s compile and program the equivalent of a hello world application… However if you want to backup the original program drop to a command prompt and type “avrdude -p t2313 -P com1 -c dasa -U flash:r:backup.hex:i” and you can always write it back via “avrdude -p t2313 -P com1 -c dasa -U flash:w:backup.hex:i”. Now open a new project in Bascom-AVR by clicking File-New and type the program in below, then hit ‘F7’ to compile and ‘F4’ to program to the chip. During this process the power switch must be in the ‘On’ position, remember you are programming a single chip computer!

The outcome when disconnected from the serial port is: a sequential lighting of the LEDs in 2 second intervals. Now it is time for you to learn some Bascom BASIC and play with the programming yourself. Start by downloading the Bascom-AVR PDF file and reading it. You can also customize my program to make the lights blink back and forth. Start by changing the timing to 1 second, then set your next goal and learn some of the language. Happy Hacking and visit some of my sponsors for deals on AVR products (I get paid when you visit them).

'Sequence LEDs
Dim X As Byte
Config PortB = Output
PortB = 0

For X = 0 To 7
 Wait 2
 PortB.X = 1
Next X

End