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(TCA8418) Does it support multiple key press???

ymhan-kutelf
Prodigy 50 points
Other Parts Discussed in Thread: TCA8418

TCA8418 Chip Bug????

TCA8418 seems to be a problem.

one or two keypad press is works well.

However, multiple 3, 4,5,6 keypad pressing => problem..!!!!!!!!

I was used as shown below.

1) Chip Setting (8x8 matrix)

  { REG_CFG,      0x19 }, 
  { REG_KP_GPIO1,     0xff }, // Keypad or GPIO
  { REG_KP_GPIO2,     0xff },
  { REG_KP_GPIO3,     0x00 },
                          
  { REG_DEBOUNCE_DIS1,    0x00 }, // Debounce Enable/Disable
  { REG_DEBOUNCE_DIS2,    0x00 },
  { REG_DEBOUNCE_DIS3,    0x00 },
                          
  { REG_GPIO_PULL1,    0x00 }, // GPIO Pull Up Enable/Disable
  { REG_GPIO_PULL2,    0x00 },
  { REG_GPIO_PULL3,    0x00 },

2) Test

case 1) 1 press : (R2, C0) => read value(21) is ok.

case 2) 2 press : (R2, C0) + (R1, C0) => read value (21) + read value (11) is ok...

case 3) 3 press : (R2, C0) + (R1, C0) + (R2, C3) => read value (21) + read value (11) + read value (13) + read value (23)

case 3 is fail. I pressed the threee keys, but event is 4 event.

I want to know. Does it support multiple key press???

I need your help..

thank you..

  • 0
    Prodigy 130 points

    What you are seeing is the "ghost key" phenomenon that occurs when three keys that form an L shape on the matrix are pressed down.  This shorts out the fourth key switch (diagonally opposite from the corner of the L), leading to the encoder seeing 4 events instead of the expected 3.  You can use 1N4148s in series with the switches to suppress the "ghosting" while maintaining multi-key support.

  • 0 in reply to Lucas Thode
    Prodigy 70 points

    Specifically: in keyboard mode, the "row" pins are inputs, with 100k internal pull-up resistors. So when you put a diode in series with the switch, the anode is at the row side, ie. the arrow on the diode "points" to the Column output.