Need help setting up my ultrasonic distance sensor

[Megahertz]

Hi, I just bought my Ultrasonic distance sensor (Datasheet attached).
I would like some help, may be few lines of code to give me a starting point for how to set it up for my purpose which is to sense the trigger pin going low when distance is less than 3 meters. I will be using 16F877A with this distance sensor which can take care of few other jobs as well.
I would also like to know how I can do the similar thing i.e. take readings of PWM output and measuring the pulse to know the distance. Again few lines of code in Pickbasicish will be better than instructions in plain english. Thanks

[mark_s]

Take a look at this page,

http://www.parallax.com/dl/docs/prod...tance28015.pdf

Regards
Mark

[Kamikaze47]

You need to set the mode and distance threshold by sending the correct command serially to the sensor. You want 9600 baud, no parity, one stop bit. The SEROUT section of the PBP manual will tell you how to do this, and the PDF you provided in your OP will tell you what commands you need to send.

The best way to get help here is to try it, and if what you try doesn't work, post the code here and i'm sure lots of help will be forthcoming.

[Megahertz]

Here goes my code for 16F676. Used this IC because I can program it in PICKIT2 & also I have jumpered my sensor around it.

Include "modedefs.bas"
DEFINE     NO_CLRWDT    1
DEFINE          OSC     4       ' OSCCON defaults to 4MHz on reset
DEFINE OSCCAL_1K 1

@ __Config _INTRC_OSC_NOCLKOUT & _WDT_OFF & _PWRTE_ON & _MCLRE_OFF & _BODEN & _CP & _CPD

PAUSE 50
Tx Var PortA.1
Rx Var PortA.0
power var PortC.1
	TRISA = %000001
	TRISC = %000001
	CMCON = 7
	ANSEL = 0
      OPTION_REG = %10000111  ' RAPU = off, PS 1:256 to TMR0
	PORTA=0
	PORTC=0
	' setup iZCD to interrupt on change
	INTCON = 0

; PortC.0 = PWM Receive ; ; ; ; ; PortC.1 = Power_On ; ; ; ;  PortA.0 = Receive Pin ; ; ; ; PortA.1 = Transmit Pin ; ; ; ; PortA.2=Trigger Pin

main:
High power
pause 100
Serout Tx, N9600, ["0x44+0x00+160+ ???"]	;	To set lower threshold distance to appx 3 meters. What should be the SUM & how do you calculate it?
Serout Tx, N9600, ["0x44+0x01+250+ ???"]	;	To set upper threshold distance to appx 5 meters
Serout Tx, N9600, ["0x44+0x02+0xaa+ ???"] ; 	To set operation mode to autonomous mode

	if PortA.2=0 then
		High PortC.2 ; led 1
	else
		high PortC.5 ; led 2
	endif
goto main
end

1) How do you calculate the SUM? any example please
Once I get to the next point, I will update here if I get stuck. Thanks

[Kamikaze47]

try something like this (taking your 1st serout line as an example):

Serout Tx, N9600, [$44,$00,$A0,$E4]

$A0 is just 160 in hex.

To work out the sum: $44+$00+$A0=$E4

If the sum is bigger than $FF then you take just the lower byte. e.g. if the sum came to $01A2, then you just use $A2.

[Megahertz]

Hi, I tried this:

main1:
High power
Pause 100
Serout Tx, N9600, ["0x44+0x00+0xA0+0xE4"] ;To set lower threshold distance to appx 3 meters
Pause 100
Serout Tx, N9600, ["0x44+0x01+0xD1+0xFE"] ;To set upper threshold distance to appx 5 meters
Pause 100
Serout Tx, N9600, ["0x44+0x02+0xaa+0xF0"] ; To set operation mode to autonomous mode
main:
	if PortA.2=1 then
		high PortC.2
	else
		 toggle PortC.5
	endif
pause 50
goto main
end

And also this:

Serout Tx, N9600, [$44,$00,$A0,$E4] ;To set lower threshold distance to appx 3 meters
Pause 100
Serout Tx, N9600, [$44,$01,$D1,$FE] ;To set upper threshold distance to appx 5 meters
Pause 100
Serout Tx, N9600, [$44,$02,$aa,$F0] ;To set operation mode to autonomous mode

but no luck - any advise?

[Acetronics2]

Hi,

The question is ...

did you use a RS232 chip on YOUR board ??? ( like in the datasheet scheme )

more ...

Could you , please , attach YOUR scheme ???

Alain

[Megahertz]

Hi,

The question is ...

did you use a RS232 chip on YOUR board ??? ( like in the datasheet scheme )

more ...

Could you , please , attach YOUR scheme ???

Alain

Hi, here is my hardware photo, just my sensor jumpered to my PICKIT2 in the following configuration:
; PortC.0 = PWM Receive ; ; ; ; ; PortA.0 = Receive Pin ; ; ; ; PortA.1 = Transmit Pin ; ; ; ; PortA.2=Trigger Pin
PWR_ON is directly connected to 5V on the PICKIT2
Also I am using TTL I/O, I have arranged the jumpers accordingly.

[Acetronics2]

Hi,

OMG ...

I also think you are exceeding the Pickit sourcing authorized current ... Especially when " pinging " ...

Alain

[Megahertz]

Hi,

OMG ...

I also think you are exceeding the Pickit sourcing authorized current ... Especially when " pinging " ...

Alain

Oops! will try everything again with seperate supply and update here. May be this is the reason that it is not working.

[Megahertz]

OK, I tried with this approach and it works, but as you will see in the code, even though the object is under 5 meters away (for eg. 4meters), PORTC.2 goes high & does not toggle. Is there something wrong with my calculation. It is working fine upto 1 meter. LED connected to PortC.2 does alterate it's toggling speed depending upon how far is the object under 1 meter. My latest code goes like this:

; Phase2: RA0=TRIG (OUTPUT) ;;;;RA1- PWM (INPUT)
w1 var word

pause 500
main1:
w1=0
High PortA.0
pause 1
Low PortA.0
pause 1
High PortA.0

main:
Pulsin PortA.1,0,w1
if w1>500 or w1=0 then 
		high PortC.2
	else
		toggle PortC.2
			pause w1
	endif
goto main1
end

[Acetronics2]

Hi,

Everything works as written ...

W1 = 500 is a distance of 1 meter ...

...

try 2500 instead ...

and note no measure will send back ... 5000 Pulsin units ( 50 000 µs )

Alain

[Megahertz]

Hi,

Everything works as written ...

W1 = 500 is a distance of 1 meter ...

...

try 2500 instead ...

and note no measure will send back ... 5000 Pulsin units ( 50 000 µs )

Alain

Hi, it works fine with 2500. Can you please explain how you calculated 2500? Thanks

[mackrackit]

500 multiply by 5 meters...

[Acetronics2]

Hi, it works fine with 2500. Can you please explain how you calculated 2500? Thanks

Being Honest ...

1) read Datasheet Page 3 ...

4: PWM - PWM Output 0－25000US，Every 50US represent 1cm

2) read PbP Manual page 133 ...

The resolution of

PULSIN is dependent upon the oscillator frequency. If
a 4MHz oscillator is used, the pulse width is returned in 10us increments.

3) The distance is 5 meters = 500 cm

from 1) and 3) ...

4) Pulse will be 500cm * 50µs/cm = 25 000 µs

from 4) and 2) ...

@4 Mhz Pulsin will return 25 000 / 10 = 2 500 units

This is the mathematical explanation of zeu thing

Alain

PS@ Dave

Don't you think I should add " Need Help " in my signature validity conditions ???

[mackrackit]

PS@ Dave

Don't you think I should add " Need Help " in my signature validity conditions ???

Yup, need help understanding data sheet.

I think Megahertz is doing fine, sometimes know where to look is a bit different than knowing what to look for.

I just spent parts of two days trouble-shooting a machine. Tried this and that, read the manual, tried other stuff, back to the manual.....
Then the great thought hit me... I wonder if that cable on the floor should be plugged into something

[Acetronics2]

Yup, need help understanding data sheet.

I think Megahertz is doing fine, sometimes know where to look is a bit different than knowing what to look for.

I just spent parts of two days trouble-shooting a machine. Tried this and that, read the manual, tried other stuff, back to the manual.....
Then the great thought hit me... I wonder if that cable on the floor should be plugged into something

Hi, Dave

This episode of our tremendous adventures lits a little light in my head ...

Would be a nice thing to get the Holy manual opened at the convenient page just clicking for "Help" in our IDEs ... ( say " mouseover " + a keystroke on KB )

Always useful to have a look to function parameters ...

Hope IDE Creators read that post ... ( thoughts to my overseas friends ...)

Alain

[mackrackit]

At one time Jeremy and I was working on a code editor with some automated fill functions but we did not get very far before other things put it on the back burner. We was using a flavor of Basic.

Then I sorta started a cross platform editor in Python but the same thing happened, got to busy to work on it.

Normet has the "fineline" editor he working on.

I wonder how many around here would be interested in an open source, cross platform, community project?

[Acetronics2]

I wonder how many around here would be interested in an open source, cross platform, community project?

I saw one nice working " IDE " ...

Called PICabc ... limited to 16F84 and assembler ...

http://www.abc-micro.co.rs/

ftp://ftp.chatnfiles.com/Microforum/...ABC/PICABC.EXE ( demo ...)

but the concept is rather interesting ...

to be honest, I must say the MiKroElektronika IDE is really handy here ...

I know one other IDE " on the rail " but was asked not to talk about it ...

Alain