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.
--- 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
>
Reply by proyectosenpic●September 11, 20102010-09-11
----- 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
Reply by mark_schilke●September 10, 20102010-09-10
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.