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Connect 4x4 dot matrix keypad to mcu only 2 wire

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feiutm9898

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i2c keypad

Usually we can connect 8 wire to 4x4 dot matrix keypad with microcontroller.

I heard that there have a technique to connect the keypad only using 2 wire.

Anyone know this? Please post the schematic here.

Thanks.
 

matrix keypad

As it is, not possible.
By modifying the keyboard and using scaled resistances on each pin (button), and using the ADC input of the mcu to detect what is pressed depending on the voltage drop, its possible.


my penny's worth.
cheers
sda
 

4x4 matrix keypad schematic

- use i2C io expander with interrupt (saves scaning job if no key press due to interrupt output pin) PCF8574 or similar - 4 ports to input 4 ports to output . look at the link **broken link removed**
- or 4 74hc165s in spi alike mode only miso and scl
(could be variations with )
- or 3 wire 74hc595 for output and 74hc165 for input
(miso mosi and scl)


May be it is already implemented Look around for i2c keypad handler chip where keypad scan and debouncing is already implemented . Maybe you will be lucky to find one .
 

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    feiutm9898

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keypad for mcu

I think Philips has AN434 that describe how to connect AT keyboard to a MCU via I2C protocol. Hope it helps.

Added after 3 minutes:

By the way, what is the dot matrix keypad? Do you mean matrix keypad with columns and rows? Sorry, if I'm wrong but this is the first time I heard of dot matrix keypad.
 

matrix keypad schematic

You can use 2 pcf8574 which are i2c I/O expander;
-one configured with all 8 lines as inputs and second with all outputs, as they form together 8*8 dot matrix; you can use, of course, just 4*4 of them.
 

4x4 matrix keypad

Have a look at HCT165 chip , much cheaper that I2C

8 parallel lines in (Keypad) , serial shift out via
2 data/clock pins on PIC.

/Bingo

Whoops missed artems post :oops:
 

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    feiutm9898

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pcf8574 keypad

is possibble but you have to use one input to a ADC converter and the keyboard has to have combinations of differents resistors so they are basically voltage dividers and mesured ..after by comparaison to a table is easy to see what key was depresed..


Cheers
 

4x3 keypad to adc

Hi,

There is another way without an ADC. It uses PWM from a 555. It all depands what you want to achive.
**broken link removed**
They say that you can connect upto 500 keys!

Good luck.
 

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    feiutm9898

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