SX/B and Ping

Mike W

Every now and again I take out my SX Tech board and try to rewrite one of the BS2 programs in SX/B. well I have been working with the Ping Sensor and SX/B the last couple of days. With the use of the Ping manual, SX/B help files, and various snippets of code from the forums I have come up with this program.
·
I am using the SX Tech Board with the 4 MHZ resonator installed, a Parallax 2 X 16 LCD display, and a Ping sensor. I am displaying the value of RawDist to the LCD
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The program seems to work, but not OK! There are dead spots in front of the ping where the value of RawDist drops and then starts to gain again. I suspect I may have timing issues.
·
I would appreciate any help or suggestions
·
Thank You
Mike W
·
·
' =========================================================================
'
'·· File...... Ping2.SXB
'
' =========================================================================
'

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' Device Settings
'

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DEVICE········· SX28, OSCXT2, TURBO, STACKX, OPTIONX
FREQ··········· 4_000_000
'

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' IO Pins
'

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Lcd····· ··········· VAR··········· RA.0··· ··········· ··········· ' LCD serial pin
Ping····· ··········· VAR··········· RA.2··· ··········· ··········· ' Ping I/O pin
'

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' Constants
'

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Trigger ··········· CON··········· 1
IsHigh· ··········· CON··········· 1
IsLow· ··········· CON··········· 0
·
LcdBaud········· ··········· CON··········· "T19200"········ ··········· ' or T2400, or T9600
·
LcdCls········· CON···· $0C············ ··········· ' clear LCD (need 5 ms delay)
LcdCR·········· CON···· $0D············ ··········· ' move pos 0 of next line
LcdBLon········ CON···· $11············ ··········· ' backlight on
LcdBLoff······· CON···· $12············ ··········· ' backlight off
LcdOn1········· CON···· $16············ ··········· ' LCD on; no crsr, no blink
LcdLine1······· CON···· $80············ ··········· ' move to line 1, column 0
LcdLine2······· CON···· $94············ ··········· ' move to line 2, column 0
'

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' Variables
'

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rawDist··········· ··········· VAR··········· Word·· ··········· ··········· ' hold raw distance
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digit·········· VAR···· Byte········· ··········· ··········· ' digitacter to send
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tempW ··········· VAR··········· Word·· ··········· ··········· ' subroutine work vars
temp1·· ··········· VAR··········· Byte
temp2·· ··········· VAR··········· Byte
temp3·· ··········· VAR··········· Byte
'

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' =========================================================================
· PROGRAM Start
' =========================================================================
'

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' Subroutine Declarations
'

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LCD_OUT····· ··········· SUB··········· 1········· ··········· ··········· ' byte to LCD
LCD_STR······ ··········· SUB··········· 2········· ··········· ··········· ' string to LCD
GET_DIST··········· SUB···· ······················· ··········· ' get Ping reading
GET_DEC····· ··········· SUB···· ······················· ··········· ' print using DEC format
'

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' Program Code
'

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Start:
· PLP_A = %0101············ ······················· ··········· ' pull up unused pins
· PLP_B = %00000000
· PLP_C = %00000000
·
· HIGH Lcd····· ······················· ··········· ··········· ' make output pin high
· PAUSE 100·· ······················· ··········· ··········· ' let LCD initialize
·
Main:
· LCD_OUT LcdBLoff········ ······················· ··········· ' backlight on / off
· LCD_OUT LcdOn1·········· ······················· ··········· ' no cursor or blink
· LCD_OUT LcdCls············ ··········· ··········· ' clear the LCD
· PAUSE 250
·
· DO
· GET_DIST··· ······················· ··········· ··········· ' ping subroutine
···
· LCD_OUT LcdLine1········· ······················· ··········· ' Line one
· LCD_STR "RawDist "······· ······················· ··········· ' line heading
· GET_DEC rawDist··········· ······················· ··········· ' data to display
·
· LOOP
'

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' Subroutine Code
'

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GET_DIST:
· Ping = IsLow································· ' make RA.2 0-1-0
· PULSOUT Ping, Trigger, 2····················· ' activate sensor
· PULSIN· Ping, IsHigh, rawDist, 1············· ' measure echo pulse
··········· ·
· RETURN
'

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LCD_OUT:
· temp1 = __PARAM1··· ······················· ··········· ' get output
· SEROUT Lcd, LcdBaud, temp1·············· ··········· ' send output to LCD
·
· RETURN
'

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LCD_STR:
· temp2 = __PARAM1··· ······················· ··········· ' save offset
· temp3 = __PARAM2··· ······················· ··········· ' save base
· DO
··· READ temp3 + temp2, temp1············ ··········· ' read a character
··· IF temp1 = 0 THEN EXIT················ ··········· ' if 0, string complete
··· LCD_OUT temp1········· ···· ··········· ··········· ' send the byte
··· INC temp2···························· ··········· ' point to next character
··· temp3 = temp3 + Z···················· ··········· ' update base on overflow
· LOOP
·
· RETURN
'

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GET_DEC:
· tempW = __WPARAM12
··· digit = "0"
·· DO WHILE tempW >= 1000··············· ··········· ' Thousands
··· INC digit
··· tempW = tempW - 1000
· LOOP
·· LCD_OUT digit················· ··········· ··········· ' Senddigit digit
···· digit = "0"
· DO WHILE tempW >= 100······················· ··········· ··········· ' Hundreds
··· INC digit
··· tempW = tempW - 100
· LOOP
·· LCD_OUT digit················· ··········· ··········· ' Senddigit digit
···· digit = "0"
· DO WHILE tempW >= 10· ······················· ··········· ' Tens
··· INC digit
··· tempW = tempW - 10
· LOOP
·· LCD_OUT digit················· ··········· ··········· ' Senddigit digit
···· digit = "0" + tempW_LSB··· ··········· ··········· ' ones
· LCD_OUT digit ················ ··········· ··········· ' Senddigit digit
·
· RETURN
'

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Capt. Quirk

I am certainly no expert, but this is what I saw

GET_DIST:

Ping = IsLow
PULSOUT Ping, Trigger, 2············ ·'but 5 normall·
Pauseus 750
PULSIN· Ping, IsHigh, rawDist, 1·············
··················································· 'requires 115 us to 18ms to measure return wave··
· RETURN
··················································· 'requires 200 us to refresh

·A lot of serial out comands in between durring the refresh time


Also I don't know how critical the speed of sound is for your application, but here is the formulae I use:

·····Sqr root·[noparse][[/noparse](((F-32)*.5555)+273)*1.4*287] = speed of sound in meters/sec

Mike W

Capt. Quirk

I appreciate your time and suggestions.

Later today I will get a chance to play around with it.

Thanks

Mike W

Sparks-R-Fun

Mike W said...
There are dead spots in front of the ping where the value of RawDist drops and then starts to gain again.

Mike W,

Can you elaborate on this or provide some example data? Do you mean to imply that you have used the Ping sensor in an identical arrangement running on a BS2 and did not experience these dropouts?

I looked over the code but nothing jumped out at me as being a glaring error.

- Sparks

Mike W

Sparks, Quirk

You have raised some thought about my project.

I am going to get my BS2 out and see·if it responds·the same way·with the·same conditions.

Baiscly the RawDist value continues to increase till I get about 4 or 5 feet from the ping, then nothing happens·until I get 6 feet·or so away then the RawDist value starts to increase again but Sporadically.

Let me see what happens with the BS2.

I'll get back

Mike·W

Mike W

For any one who is interested

I changed the trigger constant from 1 to 5

and added a pause 250 at the end of the do loop

the results were positive, so I think I need to work on my timing issues.



when I use the BS2 i get a rawDist reading of 2000 + or so.

the SX/b gives me a rawDist readings around 800 and seemes to be limited to about 6 feet

these are readings taken around my office (a lot of furniture and stuff)

im going to the basement (large flat floor and no obstructions) I'll see what results I get there



Mike W

Capt. Quirk

I found some related infomation at this thread, maybe it will help

http://forums.parallax.com/showthread.php?p=623170