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DVD UI Hack
DVD UI HACK - the hardware
To implement the hack, a stripboard with a microcontroller was constructed and installed inside the DVD chassis.
The MCU stripboard
For the purpose of this hack about 8 IO pins of a microcontroller is required and the software requirements are limited. An AtMega8 family microcontroller can easily lift these requirements. The AtMega88 was initially picked to develop the software on. The final hack uses the pin compatible AtMega48, as 4 KB flash was enough.
The schematic is very simple. Just what's required to get the MCU going and programmed with ISP. As the timing of the IR communication is very tolerant, the internal oscillator was considered sufficient.
The keyboard matrix is connected JP4 and JP3 -> JP6 is the incision to be made at the IR reciever signal. The LED is connected in a pull down manner with a current limiting resistor.
The schematic resulted in the following stripboard layout:
- which came to look like this in real life:
Installation
The PCB seen on the following picture implements the user interface of the DVD player and is the target of the hack. It has connections to the keyboard matrix and it holds the IR reciever:
The incision was made: the track from the IR reciever signal lead was cut:
The MCU stripboard was installed and connected to power, keyboard matrix and both ends of the incision. So far soo good, lets see what happens:
It just didn't work...
The MCU was just acting plain unreliable. The software didn't do as expected and at some point I couldn't even get a LED to light as it should. WHAAATS happening. I suspected that the 5V of the DVD power supply was unreliable and installed a 7805 to regulate down from the 12V line instead. Still no improvement, but I got an important clue, the 7805 became way too hot.
Well, after actually burning off two AtMegas, I realised that the small piece of black foam that I placed the MCU stripboard on, to carefully protect it from the metal chassis, was itself electrically conducting... Yes, you probably knew that already, the foam used in cases to carry integrated circuits, is electrically conducting to protect from ESD. I indeed learned that the hard way.
Cardboard is much better
The evil foam was removed and cardboard was used instead. A fresh AtMega48 was installed and I kept the 7805 in circuit though it probably wasn't needed. Everything was hot-melt-glued and this picture shows the completed hack:
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