Click on the updated schematic to view the connection of the input and output layers – two matrices – into the PIC. There is a sensing layer, consisting of Hall-effect sensors, and an output layer, comprised of LEDs indicating the latest moves on the board.
Input comes in from the board via the matrix of Hall effect sensors. These are multiplexed in order to minimize power consumption. Multiplexing is made possible by the 3 to 8 decoder. The PIC is programmed to have the decoder innervate one row of sensors at a time. Once a row is innervated, the shift register relays any high signals in that row (signifying the placement of a magnet above the sensor) to the Pic. The Pic then decodes this message to update the position of the board in its memory, and loops through the remaining rows.
Output happens in much the same way. The Pic is programmed to have the decoder innervate one row of LEDs at a time. Once the row is innervated, the shift register is loaded with that rows data in order to sink current on the lines connected to those LEDs that should be on. The decoder/shift register system loops through the remaining rows.
Not included in this diagram is the connection to the Cobox Micro. The chip displayed here, the 16F84 has run out of i/o pins, and it’s necessary to move to a giant like the 18f452 – more on that next time.