Dear Forum Members,

For my new product I have split the design in two boards.
1. Control Board.
2. Display and Keypad [ DisKey ]Board.

The Control board contains micro and other necessary logic ic's + a linear power supply.

The DisKey board contains a 9 key Matrix keypad made using tact switches and a 6 digit seven segment display [ SSD ]. The SSDs are common anode displays. The Segments of these SSDs are driven using 74LS541 [ on control board ] and Multiplexed common anodes of SSDs using ULN2003 [ on control board ]. There's no Gnd connection required for any of the component on this Diskey board.

The DisKey board is connected to control board using a 4" FRC 26 Pin ribbon cable. Though the Diskey board doesnt need Gnd I have used 6 pins of this 26 pin cable as Gnd Pin.
Pin Assignment of cable is as given below.

1. SSD a
2. SSD b
3. SSD c
4. SSD d
5. GND
6. SSD e
7. SSD f
8. SSD g
9. SSD dp
10. GND
11. SSD digit 1
12. SSD digit 2
13. GND
14. SSD digit 3
15. SSD digit 4
16. GND
17. SSD digit 5
18. SSD digit 6
19. GND
20. Keypad ROW 1
21. Keypad ROW 2
22. Keypad ROW 3
23. GND
24. Keypad COL 1
25. Keypad COL 2
26. Keypad COL 3

My Control board has solid Gnd plane. Will it give any advantage if I use Solid Gnd Plane on Diskey board too? [ It doesnt add any cost for using Solid Gnd Plane ]. Or its ok without Gnd plane since there is no Gnd Connection required on this Diskey board? Is it ok if the 6 Gnd Pins in FRC Cable are omitted and I use 20 Pin Cable instead of 26 Pin Cable.

Thanks & Regards,
Prahlad Purohit