ChessLR MCP draft circuit board
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I started to layout the circuit boards, and deciding where components will go, how they will be hooked up and with what connectors. Also putting together my final parts orders.
My first draft layout of the MCP23017 board shown here won't actually work as I missed the pull-up and LED resistors. But since I had already written this post and made the diagram, I figured I would share it anyway. The next revision will be pretty similar.
The board houses all 8 of the MCP23017 chips, and let's me connect the wires from the LEDs and Reed switches from the chess board to the chips. I'll be using female headers on the board, and male header pins from the chess board. Originally I was thinking that I would have 4 input chips (Reed switches) and 4 output chips (LEDs) but after laying the components out, and finding it optimal to have 4 upside down, it makes more sense to have a row per chip. The software will be easy enough to adopt.
MCP23017 Board
Along the top of the board I have 4 male pins for power and i2c connections. The 8 female header on the top left is a negative rail for each row of the chess board. I may just use 1 pin, as it makes more sense to just use 1 as it is common. The headers next to each chip are connected to the pins the are next to. Each chip will be put into a 28 pin DIP socket so I can replace them if needed, and so I don't solder directly to the chip, which would increase the likelihood of damaging the chip due to heat.
MCP23017 Pin Layout
Pin layout
+----- -----+
GPB0 <--> |*1 - 28| <--> GPA7
GPB1 <--> |2 27| <--> GPA6
GPB2 <--> |3 26| <--> GPA5
GPB3 <--> |4 M 25| <--> GPA4
GPB4 <--> |5 C 24| <--> GPA3
GPB5 <--> |6 P 23| <--> GPA2
GPB6 <--> |7 2 22| <--> GPA1
GPB7 <--> |8 3 21| <--> GPA0
VDD ---> |9 0 20| ---> INTA
VSS ---> |10 1 19| ---> INTB
NC ---- |11 7 18| ---> RESET
SCL ---> |12 17| <--- A2
SDA <--> |13 16| <--- A1
NC ---- |14 15| <--- A0
+-----------+MCP23017 Addresses
1 = Vdd (+), 0 = Vss (-)
A2 A1 A0 Address
0 0 0 0x20
0 0 1 0x21
0 1 0 0x22
0 1 1 0x23
1 0 0 0x24
1 0 1 0x25
1 1 0 0x26
1 1 1 0x27