Hiya Guys,
Eh I'm out looking for an interfacing chip for a 4x4 keypad so I can free some pins on a pic. So far searching through google hasn't turned up any results. Nigel's tutorials have provided me with a stable platform but taking up 8 pins will be too much for some of my projects. This is why I'm looking for an interfacing circuit so I can cut down on the pin count. Later I'll browse through some of my electronic books to see if I have any info but thats where the net comes in handy.

Cheers Bryan

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" The only way to avoid human error is to avoid the use of humans"

 

How many pins can you afford? A 3-to-8 decoder plus a buffer requires at least 3 address and 1 data bit (Total 4).

 

This method uses only 1 pin (I guess that is the minimum possible )
http://www.edn.com/article/CA512131.html

__________________
Instruite
http://www.icesociety.org
=====================
Ideas that work,
Concepts that sell.
=====================

 

Why not use a PIC to interface it to your PIC. Any other solution is going to require another chip anyway. If you choose one with an internal clock you wouldn't need any other components except the keyboard and the Pic. You could communicate via RS232 (without MAX232) or I2C. You could even put an LCD on it and call it a terminal.

Mike.

 

Thanks for that link Intruite, it looks like a top way to go and I might have to give it a try. One thought today was to use an old 16f628 to handle the keypad processing and pass on via serial to the main pic. That way I won't have to worry too much with a huge code to debug.
Checkmate I was thinking of 4 pins but I'm not sure as to which 74 series chip to use but I'll checkout that 3-8 decoder you mentioned.

Cheers Bryan

__________________
" The only way to avoid human error is to avoid the use of humans"

 

Hi bryan1,
Well you asked for the least pins and I gave you the solution for the same
I know making software for that configuration will be tough but if you are able to implement it sucessfully, then do post the software so that those who want to interface keyboards can use it

__________________
Instruite
http://www.icesociety.org
=====================
Ideas that work,
Concepts that sell.
=====================

 

The chip you are looking for are 74C922 and 74C923 at price some six UK pounds plus postage.

I agree with Pommie that a PIC would be a much cheaper solution.

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L.Chung

 

You must of been reading my mind Pommie cause as soon as I posted my comment I saw yours. I looked at that 74c922 chip circuit this morning but at $23.00 each it will be cheaper to go with a pic. I'm mucking around now with mplab on the 628 program and hopefully I'll have it going by the end of the weekend. Besides it looks like a perfect small project to start with. When I get everything all sorted I'll update my website with the design so everyone can use it.

Cheers Bryan

__________________
" The only way to avoid human error is to avoid the use of humans"

 

As most other people have suggested, use an extra PIC as a dediciated keyboard controller, and feed the output from one pin as serial information - my tutorials have everything you need!.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

After all, PIC does stand for Peripheral Interface Controller. :lol:

Mike.

 

Yea Thanks Nigel, your tutorials was the first place I looked so with a few tweaks and groans I'll get it setup in no-time. Also one thing you can be sure of I'll include a credit to Nigel in any asm code I use from the tutorials.

Cheers Bryan

__________________
" The only way to avoid human error is to avoid the use of humans"

 

Actually, it's meaning is generally shrouded in mystery?, although that is what many people (including myself) consider it to mean. MicroChip themselves don't seem able to give a definitive answer?, mind you the name was there a long time before MicroChip were!.

Likewise AVR stands for "we were trying to copy a PIC and steal some of their market, so we made up a three letter name to try and be as close as possible" :lol:

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

People always told me that it means Programmable integrated circuit
But I heard different from many other people.
I thought AVR stands for A Very Ridicules microcontroller. :lol:

__________________
Robotics is heaven in my book.

 

Bryan , you could allways try mine & jays switch multiplexer ..
it requires only 1 output pin and 1 input pin on the pic..
the idea is to cycle through a count on the pic , till a switch is pressed ..
when a switch is pressed the pic "knows" which one is pressed because it will corrospond to which part in the cycle the switch was pressed..

http://www.electro-tech-online.com/v...r=asc&start=15

 

well, although i know that electro-tech-online is highly biased towards PICs and I myself like PICs but i do want to say that AVRs are simply not ridiculous!

the AVR microcontroller is being taught in courses all around the world. and a huge number of students and hobbyists use it in their projects.

one thing i want to say here is that there is no point in saying that the AVR is bad or the PIC is good etc because none of us are the actual developers of the PIC or the AVR and niether are we the sales and marketing representative of microchip or atmel.

if someone starts off with a project and he thinks that it will be easy with a specific microcontroller then he would definitely choose it. so anything that works for you is good. be it the PIC or the AVR