Resurecting a internet tablet (Eken M001) - Dead battery

So, I've had this internet tablet for a while now. I bought it cheap, in the early years of the tablet revolution. It's been sitting on my shelf unused, as it couldn't compete with 1.gen Ipad.

 
A little while ago I tried to turn it on again, to be used in a project idea I have. However, it had given up the ghost. After opening the case and inspecting it, it turned out that the battery was completely dead. Zero volts over the cells, and the balancing board corroded beyond recognition!

Turns out, a suitable battery was expensive, more expensive than I was willing to spend on this project. I thought, therefore, I could hack an inexpensive RC pack. So I bought got hold of an RC pack and a new balancing/protection board.

After peeling everything (carefully) apart (because they can explode), I de-soldered the cells free. If you attempt this, please take appropriate safety precautions. I then soldered the cells onto the protection board, and applied copious amounts of capton tape.

To get the protection board working (activation), a charging current needs to be applied. Otherwise no voltage will appear across the load output. (This needs to be done every time the cells are disconnected from the board). The simplest solution it to connect the new battery to the tablet.

I had to reflash the tablet with firm ware, probably because of the prolonged powerloss.

And then everything worked perfectly! Battery reading and everything!! Well chuffed :) I reckon there is about an hours use on full screen brightness. Not a huge amount, but for what I'm going to use it for, it doesn't matter anyway.

What's inside a really expensive LED lamp light

I bought these really expensive LED lamp light for our new outdoors night lights. They even came with a 2 year warranty. I plashed out on these LED based lights, because:

1. They use less energy, hence are more environmentally friendly.
2. They last (supposedly) longer, hence are cheaper in the long run and are, because of this, more environmentally friendly as fewer materials are consumed.

 As a foot note, do not replace working lamps (incandescent or fluorescent) until they eventually burn out.

 

Since they failed in little over a year, I thought I'd do a postmortem on one of them.

The top is also a lens cover, and it came off easily despite being glued on, revealing the LED circuit board.

 

The circuit board substrate is metallic, and the board is thermally connected to a pretty hefty lump of metal with some white thermal paste, most likely silicone based. It is probably there to dissipate heat from the LEDs, or maybe give the lamp that "premium" feeling weight.

 

Now, removing the heat-sink and LED board reveals a second circuit board. Cutting of the mains legs frees the second circuit board.

The second circuit board is a relatively simple thing, a single sided PCB with a handful of components. There is a mix of surface mount and through whole components. Looking at this second PCB I feel a little disappointing, as this is where I would expect my very expensive LED lamp to distinguish itself from any cheap LED lamp, but at first glance it is a really simple passive circuit!

 

 

This second circuit board is just a simple diode bridge rectifier, with a few additional passive components thrown in the mix. On the AC input side are two resistors and a capacitor: 33 Ohm / 1 W, 1M Ohm / 0.25W, and a 0.90uF / 400V film capacitor. On the DC side there is one 2.2 uF / 400V polarized capacitor and a 300k Ohm SMD resistor. The diodes used are marked M7, which is a general rectifier diode rated for 1 A / 1000 V. I have 220V / 50Hz AC in my house, so straight of the rectifier bridge there will be a very rough 220V "DC".  I've not reverse engineered the circuit, but I'm assuming something is being done to lower the DC voltage, because the LEDs would not be able to take 220V.

The LEDs are "Natural" white 2835 SMD LEDs, which have a forward voltage of 3.2 V and 60 mA continuous forward current. There are nine of them in a straight series. This means the ideal DC voltage is 28.8 V.

I've traced the LED circuit to bring out the serially connected LEDs.

 

So there you have it. Certainly not worth the premium price, and since they lasted a shorter time than a normal incandescent equivalent, this is a definitive "Do not buy!".

Power & IO PCB for Attitude System (Thesis)

Over the last couple of days I did another module for the attitude system stack. The last one I did was the uC PCB, which won't be used in the final system, due to its low processing power. This  new power and IO will be part of the final system, as it will take care of the external power and interface convertion.

First of all, the PCB takes power and regulates the voltage down to 1.8V, 3.3V, and 5V for all the sensors and uC/FPGA. I was a little unsure of wether I should put in a bridge rectifier on the power input, to make sure the polarity would always be correct. In the end I skipped it. Secondly the PCB has a USART signal converter for external I/O, together with a 9 pin DSUB-F connector. This  is my primary interface.

I also put on a RJ45 socket, in case I also implement an  ethernet interface, but with just a simple 2x4 header.

Finally I have to commend the guys at iTead Studio for their excellent service. I was very pleased with the last batch of PCBs they made for me, at a price you just can't beat. But this time they kindly pointed out to me that I was missing two drill holes for the RJ45 socket (see picture). That is just awesome! Thank you!! The error was due to the way STARCAD was set up not to include non plated drill holes in the drill file. Quickly fixed, and updated files sent away. Now for the waiting part ;-)

Just another adapter III: LCD adapter - Final

Back from holls, and the components I neded to finish up this project was waiting for me in the mail. However, on closer inspection I found an airwire in the PCB! I could fix this with some trickery, but I decided not to, as it only affects back-light controll (you can see the missing trim-pot).

Some quick soldering of the contrast trim-pot and the missing 8x2 header, and the build was ready for some in-circuit testing. And the build was a success! Even in relativly simple builds like this, you really don't know before you turn it on.

Because of the air-wire, I won't post the schema and design unless requested.

Just another adapter II

So, the PCB is now drilled and partially populated. The two 10-Pin headers for the STK500 are soldered on, as well as the single row (1x16) LCD connector and a LED. I keep the photo-resist until the very last moment, only then do I remove it on the spots I want to solder, using q-tip dipped in acetone. This way, the photo-resist protects the copper and keeping it from oxidising.

I ran out of single row (or double for that matter) female headers and I didn't have the right trim-pot either, so I will have to wait until after the holls to finish this one. Part are on order.Well, at least the LED power-indicator works.

Parts-list, schematics, and PCB to come when the build is done.

Just another adapter

I seem to be making allot of different adapters lately. This is the freshly made PCB/PWB for a LCD adapter for the STK500. More info to come later, that, and I'm trying out blogging from my Android phone :-D

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STK500 10-Pin I/O-Adapter

The STK500 development kit is excellent, and those 10-pin headers are great for making standard expansion boards for the headers. But sometimes all I need is quick access to a pin, for connecting the kit to a bread-board or similar. Nothing ready-made seemed to be available, so I made a quick-and-dirty adapter. Taking the standard 10-pin header and breaking them out into a single 1x10 standard 2.54mm row, adding only a LED for power indication.

PCB available for download soon...