Microbook - Hardware
Most parts are clearly visible on the prototype:
Full schematics and firmware
The core is the Atmega328p microcontroller.
Microsd card slot is connected to it directly, over SPI.
Nokia 5110 screen is also linked by SPI.
The screens in a nice wrapper can be obtained from China, on ebay, i.e. here.
On the bottom there are 4 buttons and 2 debug LEDs.
The 32Kb FRAM chip, FM24W256 is connected over I2C.
Firmware access pattern assumes FRAM, or other type of NVRAM.
You could use a regular flash/eeprom chip or even AVR's internal eeprom, but FRAM have a nearly unlimited write cycles, and write speed is the same as read speed, which opens up some possibilities.
The memory holds a list of books opened, with current positions, it stores the position on every page flip, menu locations/settings on every change and button press, and so on.
This allows you to completely turn off the device at any time, then power it on and have it in the same state it was at power off. Convenient and power-saving.
The power supply consist of 3 ICs.
MAX660, doubles the 2-3V from the solar panel to 4-6V needed for the charger.
MAX1555, a LiPo charge controller, with the battery attached to it.
There is a power switch between the battery and the rest of the circuit, so it keeps charging when turned off.
After the battery there is a MCP1252 charge pump voltage stabiliser, giving out 3.3V.
A line goes from the battery to the Atmega's ADC, across a voltage divider, to monitor battery charge level.
All this fits on a rather simple two sided 50х60mm PCB.
PCB trace (clean one for printing is in the software package):
The only hardware issue found to date is the lack of a case.
3D printing helps, but just barely.