4 x 3 keypad using 1 analog input

Started by mark_schilke September 10, 2010
Hi, Folks!

I read the ED article in file "1 pin Keypad.PDF" posted by dave_mucha, and compared it to the "4x4 Keyboard with 1 Input" tip in Microchip's Tips & Tricks guide. The latter has far fewer components external to the PIC. Has anyone met with good success using the method in that tip?

The device I am designing will use a 4 x 3 keypad, with a layout similar to a Touch Tone telephone. I posted two files ("4 x 3 keypad using 1 analog input.xlsx" and "4 x 3 keypad using 1 analog input.xlsx") that show some details of that design. The pushbuttons that I intend to use have metal contacts, so resistance build-up and re-calibration of the analog input ranges should not be an issue. The PIC of choice will have a 10-bit resolution, but I imagine an 8-bit A/D would be good enough.

I welcome your comments and suggestions!
MfG,

Mark Schilke

hahaha...
what an old applet!!!
Please see this. You just has get me through the Time tunnel, thanks!
http://www.piclist.com/techref/microchip/4x4key1ad7r.htm

dennis Cralwey

----- Original Message -----
From: "mark_schilke"
To:
Sent: Friday, September 10, 2010 8:35 AM
Subject: [piclist] 4 x 3 keypad using 1 analog input
> Hi, Folks!
>
> I read the ED article in file "1 pin Keypad.PDF" posted by dave_mucha, and
> compared it to the "4x4 Keyboard with 1 Input" tip in Microchip's Tips &
> Tricks guide. The latter has far fewer components external to the PIC.
> Has anyone met with good success using the method in that tip?
>
> The device I am designing will use a 4 x 3 keypad, with a layout similar
> to a Touch Tone telephone. I posted two files ("4 x 3 keypad using 1
> analog input.xlsx" and "4 x 3 keypad using 1 analog input.xlsx") that show
> some details of that design. The pushbuttons that I intend to use have
> metal contacts, so resistance build-up and re-calibration of the analog
> input ranges should not be an issue. The PIC of choice will have a 10-bit
> resolution, but I imagine an 8-bit A/D would be good enough.
>
> I welcome your comments and suggestions!
> MfG,
>
> Mark Schilke

Here's my recent implementation of a similar idea. I'm reading 10 switches and it works great. Since the ADC range is divided into 10 regions, there's plenty of separation between values and no need to worry about calibration.

The only caution is to make the resistance values small enough to match the ADC input impedance. 470 resistors worked great. When I made a second version with 2k resistors (since I happen to have a box of those), I had some problems.

http://digital-diy.com/home/handy-tips/229-10-keys-on-one-port-pin.html

Jon

--- In p..., "mark_schilke" wrote:
>
> Hi, Folks!
>
> I read the ED article in file "1 pin Keypad.PDF" posted by dave_mucha, and compared it to the "4x4 Keyboard with 1 Input" tip in Microchip's Tips & Tricks guide. The latter has far fewer components external to the PIC. Has anyone met with good success using the method in that tip?
>
> The device I am designing will use a 4 x 3 keypad, with a layout similar to a Touch Tone telephone. I posted two files ("4 x 3 keypad using 1 analog input.xlsx" and "4 x 3 keypad using 1 analog input.xlsx") that show some details of that design. The pushbuttons that I intend to use have metal contacts, so resistance build-up and re-calibration of the analog input ranges should not be an issue. The PIC of choice will have a 10-bit resolution, but I imagine an 8-bit A/D would be good enough.
>
> I welcome your comments and suggestions!
> MfG,
>
> Mark Schilke
>