I got my mbed rapid prototyping microcontroller based on Arm Cortext-M3 a few weeks ago. It is an mbed NXP LCP1768 and what I like about it is that it has a built in ethernet support and it is very user friendly 40 pin DIP package. There are 4 pins correspond to (TD+, TD-, RD+, and RD-). All I have to do it to connect it to an ethernet cable, plug it into my linksys router, upload my program and run it.

Programming is done thru an online compiler which results in a BIN file. I don’t need a separate microcontroller programmer for this. When you plug mbed into your usb port, windows will detect a new “drive” (something like a usb thumb drive), and all you need to do to “program” is to just copy the BIN file and paste it into the “drive”.

Here’s a photo of how it was connected (Still messy).

I bought a cheap ethernet cable, cut one end off and connect pins 1,2,3,6 to the mbed’s ethernet pins. mbed.org has some documentation on the pin connections. Notice that I temporary used alligator clips for the connections. That will do for now until I’ve created a proper mounting board with RJ45, SDcard and USB ports.

Here’s a closer look

I’ve created a simple HTML file just to test it. Mbed has an ethernet library so no need to create your own network stack. Just use it. I’ve set it to output some debug messages over a serial port (you need to load a driver so windows will recognize your mbed as a com port). In linux, no drivers needed. In my setup it was mapped as /dev/ttyACM0.

Here’s a screenshot of a running web server on my mbed.

The smallest screen is my linux command line terminal where I’ve shown the contents of the html file. The middle screen is my com port terminal similar to window’s hyperterminal where I can view all my debug message, and finally the one at the background is my browser where I connected to my mbed’s webserver.

If you were wondering what’s inside a laptop battery, you’re just like me. Fortunately I have an old, defective laptop battery. Just like the show “Mad Labs”, smash labs, and mythbusters, I opened it up and here’s what it looks like.

There are 4 Li-ion cells and at the center is some sort of a charge controller.

The main chip of the laptop battery

This seems to be some sort of temperature monitor which senses the temperature of the cells.

This one, I don’t know. A diode perhaps that senses temperature also?

This is how the cover looks after screwing the switch and pressing down the mini solar module/solar cell with double sided adhesive tape.

Next would be to tape the terminal block to the battery.

The way I did it is to tape a horizontal terminal block and then add 2 vertical terminal blocks on each side. One side would be wired to the negative terminal of the battery and the other side to the positive. The positive side goes to the switch first and not directly to the battery so I can turn it on and off when needed.

Below is a closeup view of the blocking diode. I used an old IN4001 . The diode has a white bar. The white bar is wired to the terminal (going to the side of the battery) while the other side of the diode goes to the ( ) side of the solar cell.

Here’s how it looks from the other side. At first I thought of using just 1 big LED but later on, I decided to use many smaller bright white LEDs.

Here’s a top view shot

Here’s a closeup of one of the LEDs. One side is connected to the (-) vertical terminal block and the other side at the ( ) terminal block.

Top view shot of the 6 LEDs. 3 on each side. The LEDs in a way hold the 2 vertical terminal blocks together which is kinda neat.

Side view.

Lastly, here’s the finished product.

Technorati Tags: diy, diy solar project, diy solar lantern, solar lantern, solar LED lights, solar lights, solar powered lights

To continue my DIY Solar Lantern project, I’ll now talk about the charging module. This is composed of the Nicad battery, Solar Cell, and a diode.

Charging Module

A diode is an electronic component that allows current to flow to one side but not the other way. For solar charging, we would be using a diode to allow current to pass from the solar cell to the battery.

However, during night time when there is no sun, a small current goes from the battery to the solar cell. This is what we would like to prevent and the diode blocks that current.

This is a simple charging circuit but it does not protect the battery from over charging. Maybe in the future, I’ll design something that would automatically switch off the charging process once the battery voltage goes to a pre-determined value. But for now, I’ll just make my DIY solar lantern as simple as possible.

Overcharging is the number 1 cause of battery damage. So for now, I’ll just have to estimate the number of hours I’ll leave my solar lantern under the sun.

The Solar Cell

I’ll be using a mini solar module (solar cell) which has an output voltage of 5v and a current of about 70mA at full sunlight. (This makes about 0.35watts of power).

How long does it take to charge the battery?

This depends on the capacity of the battery. In my case, I have a 280mAh Nicad battery. If my battery is fully depleted, it would take around (280mA/70mA= 4 hours) to fully charge.

Putting it all Together

First is to make a hole at the center of the canister cover. This is where the wire from the solar cell would pass through. I outlined the underside of the solar cell with a double adhesive tape so it will stick well on the cover. This also protects the solar lantern from getting rain so that water won’t go into the center hole where the wire goes. (It is not water proof though so I don’t suggest leaving yours outside if it rains). I might put some silicon someday (the one used in making aquariums) to make it waterproof.

On the underside, I also added a double adhesive tape to close the center hole where the wire passed through. I added some more double adhesive tape and then press down my Nicad battery. I then drilled a hole for the switch.

To be continued….

Technorati Tags: diy, diy solar lantern, solar lantern, solar gadget, solar led lights, solar powered light