SCHEMATIC
A .pdf file of my schematic can be viewed here.
The prototype of my Digital Cookbook was assembled with wire wrap and then soldered in place.
Difficulties
Both the LCD module and the DataFlash chip were difficult to work with. The LCD had no wires or pins but rather 20 closely
spaced pads while the DataFlash chip is meant for surface mounting. I didn't know of either situation prior to ordering
the parts. But with a lot of patience and luck and a little bit of skill I was able to use them.
Another problem I had with the DataFlash chip was the voltage difference. Most of the board runs off of 5V supplied from
a LM7805 regulator. The DataFlash chip is supposed to have a 2.7V supply. This was generated using a LM317 adjustable
regulator, a 240-ohm resistor, and a 280-ohm resistor. The subcircuit was copied from the LM317 datasheet. This makes the
output approximately 1.25V + ( 1 + 240/280 ) = 2.7V.
However, the datasheet for the AVR 8515 says that the lowest voltage it will recognize as a high input is 0.6Vcc, or 3V
in this case. I decided to place a 74125 buffer running at 5V in between. I was hoping it would have a wider noise margin
which would recognize 2.7V as being high and then boost it to 5V so the AVR could recognize it as high. However this did
not work.
The next step was to raise the supply voltage of the DataFlash chip. It is meant to operate at 2.7V but the datasheet says
it can run at as high a 3.6V. So I changed the 280-ohm resistor in the LM317 subcircuit to a 430-ohm resistor (actually
implemented as 330-ohm + 100-ohm) making the voltage 1.25V + ( 1 + 240/430 ) = 3.5V. Surely 3.5V would be recoginized
as a 1. However this still did not work.
You would think that having a buffer in between would not hurt, but it did. I removed the buffer and instead placed
a 220-ohm resistor in between the DataFlash output and the AVR input. This finally worked.
Going the other way (AVR output, DataFlash input) was much easier. The AVR outputs were 5V and according to the DataFlash
datasheet it can handle inputs up to 6.25V. 330-ohm resistors were used to connect the outputs to inputs.
Resistors are used so that some voltage can be dropped across them if necessary. I don't believe the values of these
resistors is critical as long as they are the same order of magnitude.