keypad encoder

[Mel_noypi]

hi

I have a project which use a 4x3 keyapd with keys position similar to that of an odinary teliphone. I have Purchase a MM74C922N keypad encoer. the problem is that i found out that it is a 16 bit keypad encoder intended for a 4x4 keypad..
im looking for a IC keypad encoder which is applicable to the 4x3 keypad which i intended to use.

do any one knows any part number for a common keypad encoder IC that i can use for my project.

tenx.

 

[Nigel Goodwin]

hi

I have a project which use a 4x3 keyapd with keys similar to that of an odinary teliphone. I have Purchase a MM74C922N keypad encoer. the problem is that i found out that it is a 16 bit keypad encoder intended for a 4x4 keypad..
im looking for a IC keypad encoder which is applicable to the 4x3 keypad which i intended to use.

do any one knows any part number for a common keypad encoder IC that i can use for my project.

Just ignore the extra pin, you don't need a different IC - you may have to add a pull-up or pull-down resistor to it, check the datasheet for the chip.

 

[Mel_noypi]

Yes i did at first ignore the pin for column 4 since 4x3 keypad do not have a 4rt column. but it output a different binary codes. when i study its datasheets i found out why it is not applicable to my keypad becouse the keys positioning of a 4x3 and 4x4 are different, so their are different row and colomn combination needed to represent the values or numbers printed on each keys.so as a solution i thought i would just adjust the row and column combination so that it could fit the nessesary position for the IC. but i was wrong it cant be done. so i decided to find a replacment IC.

 

[mstechca]

If you are unlucky with part numbers, you could make yourself an encoder.

Just use a bunch of diodes to make one, and connect some anodes together.

As for finding an encoding chip, the best you will get is either a 8-3 encoder or a 16-4 decoder. The 8-3 encoder converts a number from 1 to 8 into a 3-bit binary number. The 16-4 encoder converts a number from 1 to 16 into a 4-bit binary number.

Try Nigel's suggestion first and make sure that the top 4 values are pulled down. That way you get an encoder from 1 to 12 instead of 1 to 16.

 

[Mel_noypi]

(':wink:')
ok, thanks both of you for the ideas..i'll be experimenting with it

 

[Nigel Goodwin]

Or you could use a PIC to make an encoder? - one of my tutorials reads a 4x4 HEX keypad using a PIC, and gives the changes required for a 4x3 keypad. It uses a look-up table, so you can allocate any value to any key.