My efforts to create a Kindle Keyboard lit cover

[ron0909]

Hi all,

I thought I'd share my efforts to create a lit cover for my Kindle Keyboard. I tried a few different ways using brass tubing etc. with the light hinged but ended up with a much simpler removable light. A trip to 'The Source' (radio Shack in the US) produced a USB powered LED lamp on a flexible neck. They have 2 versions. One with 5 LED's and one with 2. The 2 LED version is even too bright at times so I opted for that one. What inspired me to use these lamps was the sale price of $2.95!

The flexible neck was originally 12 inches long so after peeling off the plastic coating on the usb connector, I was able to de-solder the connector and cut back the flexible neck. A bit of heat shrink sealed it up beautifully after re-soldering. I had an old broken USB hub from which I pillaged a female USB jack. If you need the pin configuration a quick Google search will tell you. The cover I used is the stock Amazon leather cover. I had to cut it open carefully on the inside in order to mount the USB jack and run the wires to the metal clips.I sanded the metal clips until the black coating was removed down to the bare metal. Both sides were sanded as I don't rightly know where the actual contact is made within the Kindle. Soldering to the base of the cover's clips was not as difficult as I had anticipated
and made for a great connection. Lastly I had a thin plastic sheet that I covered with cheap black fabric to cover up my surgery. It was a glued down with cheap Elmer's spray adhesive.

If anyone would like a more detailed instruction page, I'd be happy to throw one together
without the rambling I think the total cost of this project would be about 6 bucks if one had to purchase the USB lamp, some heat shrink tubing and the USB jack. Obviously the cover is extra

[itakatz]

I measured the voltage to be about 4.06V, but do you happen to know how much current can be drown from these terminals? Can I hook 3 or 4 LEDs? I though of attaching 2 on each side, instead of using a ready usb-light.

Thanks.

[ron0909]

It might be found on the battery itself. I believe they are capable of providing 1900 mAh at 3.7v. As a guess, turning off wireless networking and 3g (I don't have 3g personally) would probably more than make up the current draw from a few bright low powered LED's. With my 'system' going for hours every night I find I need to recharge every other day. It might seem a lot but really isn't as I rarely run the battery down below 40%. Maybe 20 mA 5mm bright white LEDs? 2 per side with all 4 wired series/parallel...
Hope this gives a little food for thought
Ron

[itakatz]

The information on the battery is the total capacity, not current (therefore it is measured in mAh, which is milliamps per hour. 1920 mAh means you can get a current of 1920 mA for one hour, or 192 mA for 10 hours, etc. But it doesn't give information about the maximal current you can draw from the terminals without damaging the device. Since each LED needs about 20 mA for regular operation, I guess 2 or 3 won't be a problem. Btw, they must be connected in parallel, since the output is only about 4V, which means the currents will be additive (20mA per LED).

[knc1]

Originally Posted by itakatz

The information on the battery is the total capacity, not current (therefore it is measured in mAh, which is milliamps per hour. 1920 mAh means you can get a current of 1920 mA for one hour, or 192 mA for 10 hours, etc. But it doesn't give information about the maximal current you can draw from the terminals without damaging the device. Since each LED needs about 20 mA for regular operation, I guess 2 or 3 won't be a problem. Btw, they must be connected in parallel, since the output is only about 4V, which means the currents will be additive (20mA per LED).

The general rule for the type of battery used in the Kindle is, the peak current draw is twice the mAh rating. This is a "surge" rating not a continuous rating.

Which is why Kindles have batteries with a 1500 mAh or larger "storage capacity" rated battery.
The 3G modem/radio card draws 3 amps (1500 mA * 2) while actively transmitting. (these are "burst" transmissions done at the battery's "surge" rating).

The battery in a Kindle is not the size it is because Amazon wanted you to be able to go a month between re-charges. That's the smallest capacity battery that will run the 3G card.

None of which applies to what the limit of the current draw from the top lamp connector might be.

That is a "switched" power connector.
The limit is that of the electronics used to do the switching.
If the (solid state) switch is only rated at 20ma - then you can only pull that much current from the connector.

[itakatz]

Originally Posted by knc1

The battery in a Kindle is not the size it is because Amazon wanted you to be able to go a month between re-charges. That's the smallest capacity battery that will run the 3G card.

And what about the non-3G models? They probably have the same battery, right?

Originally Posted by knc1

None of which applies to what the limit of the current draw from the top lamp connector might be.

Of course, it agrees with what I wrote in my former message. I guessed there is some current limit to the lamp connector, and you are saying one must examine the internal electronics of the switched connector in order to get the current limit.
Now all is clear, thanks

[knc1]

Originally Posted by itakatz

And what about the non-3G models? They probably have the same battery, right?

Correct.

Originally Posted by itakatz

Of course, it agrees with what I wrote in my former message. I guessed there is some current limit to the lamp connector, and you are saying one must examine the internal electronics of the switched connector in order to get the current limit.
Now all is clear, thanks

Correct.
I was countering parts of the thread that wanted to throw a bunch of LEDs into the light fixture because of the size of the battery.
If the "stock" cover only uses one LED, then that might be the current limit of the led supply.