controlling interference

mike_1234 · 2005-11-30 22:23

Does anyone have suggestions as to how to control emf fields?

My stamp has 13 inputs, (just reading if a switch is·high or low) is there anyway i can
prevent the other inputs from picking up the status of the other inputs

thanks

Mike

Jon Williams · 2005-11-30 22:27

Are you using pull-ups (active-low) or pull-downs (active-high) on your inputs?

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Jon Williams
Applications Engineer, Parallax

mike_1234 · 2005-11-30 23:35

active high

Jon Williams · 2005-12-01 00:33

Then on each of your inputs you should have a 10K resistor between the I/O pin and ground. Do you?

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Jon Williams
Applications Engineer, Parallax

mike_1234 · 2005-12-01 01:06

yuppers

mike_1234 · 2005-12-01 01:07

in the manual if you look at the button function i have my circuit exactly how they show it

Jon Williams · 2005-12-01 01:42

Can you post your code?

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Jon Williams
Applications Engineer, Parallax

mike_1234 · 2005-12-01 16:08

sure.. also can you tell me how to control my switch bounce

'{$STAMP BS2pe}
'{$PBASIC 2.5}

RD_E2PROM_Switch PIN 14

Input_Pins_0_13 VAR INS

Value_To_Store VAR Nib
Stored_Value VAR Nib
WR_E2PROM_Addr VAR Word
RD_E2PROM_Addr VAR Word

Initialize:
WR_E2PROM_Addr = 0
INPUT RD_E2PROM_Switch

DO
GOSUB Chk_Inputs
LOOP
END

Chk_Inputs:
PAUSE 100
IF (Input_Pins_0_13 <> 0) THEN GOSUB Convert_Decimal '<> means NOT EQUAL
IF (RD_E2PROM_Switch = 1) THEN GOSUB RD_E2PROM
RETURN

Convert_Decimal:
IF (Input_Pins_0_13 = 1) THEN
Value_To_Store = 0
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 2) THEN
Value_To_Store = 1
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 4) THEN
Value_To_Store = 2
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 8) THEN
Value_To_Store = 3
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 16) THEN
Value_To_Store = 4
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 32) THEN
Value_To_Store = 5
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 64) THEN
Value_To_Store = 6
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 128 ) THEN
Value_To_Store = 7
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 256) THEN
Value_To_Store = 8
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 512) THEN
Value_To_Store = 9
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 1024) THEN
Value_To_Store = 10
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 2048) THEN
Value_To_Store = 11
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 4096) THEN
Value_To_Store = 12
GOSUB WR_E2PROM
ENDIF

IF (Input_Pins_0_13 = 8192) THEN
Value_To_Store = 13
GOSUB WR_E2PROM
ENDIF
RETURN

WR_E2PROM:
STORE 8
WRITE WR_E2PROM_Addr, Value_To_Store
WR_E2PROM_ADDR = WR_E2PROM_Addr + 1
RETURN

RD_E2PROM:
STORE 8
DEBUG "E2PROM CONTENTS", CR, CR
FOR RD_E2PROM_Addr = 0 TO WR_E2PROM_Addr
READ RD_E2PROM_Addr, Stored_Value
GOSUB Send_To_Display
NEXT
RETURN

Send_To_Display:
DEBUG "Location ", DEC RD_E2PROM_Addr, " = ", DEC Stored_Value, CR
RETURN

Jon Williams · 2005-12-01 16:50

The problem is that you "Chk_Inputs" subroutine does no debouncing -- it's probably contact bounce that you're having troubles with. Download our "StampWorks" book; it has a project on scanning and debouncing multiple inputs.

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Jon Williams
Applications Engineer, Parallax

mike_1234 · 2005-12-01 17:19

ok thanks

Vern Graner · 2005-12-01 17:25

mike_1234 said...
Does anyone have suggestions as to how to control emf fields? My stamp has 13 inputs, (just reading if a switch is high or low) is there anyway i can
prevent the other inputs from picking up the status of the other inputs?

There's some good discussion about how to reduce false triggers (usually contact bounce related) in this thread in the ParallaxEFX forum:

http://forums.parallax.com/showthread.php?p=554164

And also some information on maximum switch distance and some alternative switch strategies in this thread:

http://forums.parallax.com/showthread.php?p=556608

Hope that helps!

Vern

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Vern Graner CNE/CNA/SSE    | "If the network is down, then you're
Senior Systems Engineer    | obviously incompetent so why are we
Texas Information Services | paying you? Of course,if the network
http://www.txis.com        | is up, then we obviously don't need
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controlling interference

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