MPXA4115A picbasic code

**bitmaniac** · - 19th January 2010, 17:09

Sure there is a timing (delay) problem.
You gave a more sophisticating explanation.
You gave me an idea.May be we I will hook the oscilloscope to see the exact pulse..

**Acetronics2** · - 19th January 2010, 17:50

Hi Alexandros

I had committed that from what you wrote ...

Code:

'****************************************************************************
' (c)2009 Alexandros Zahariadis (E.A.TH.) Greece *
' Electric Glider electronic switch to be used in F3J-GR competitions.
' The device will cut-off motor if 200m ALT reached or 30seconds passed
' whichever comes first!
' There is also a status led option which idicates if you have reached 200m
' or not (may be because of luck of power!)
' steady led -> 200m ALT reached , blinking led -> 30 secs passed.
' NOTE: after a lot of experiments and because of code execution speed
' I use direct ADC raw sample values without converting them to meters first!
'    :: thanks to Acetronics (Alain) and picbasic forum for codding ideas ::
'****************************************************************************

'@ DEVICE FCMEN_OFF
'@ DEVICE IESO_OFF
'@ DEVICE BOD_ON
'@ DEVICE CPD_OFF
'@ DEVICE PROTECT_OFF
'@ DEVICE MCLR_OFF
'@ DEVICE PWRT_OFF
'@ DEVICE WDT_OFF
'@ DEVICE INTRC_OSC

@    __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _BOD_ON

INCLUDE "modedefs.bas"

clear
DEFINE OSC 4
define PULSIN_MAX 250
;DEFINE DEBUG_REG GPIO
;DEFINE DEBUG_BIT 2
;DEFINE DEBUG_BAUD 9600
;DEFINE DEBUG_MODE 1

OSCCON = $60           ' $60:4 Mhz $70:8 Mhz int.
CMCON0 = 7              'TURN COMPARATORS OFF
TRISIO = %00001010      'Set GPIO1 and GPIO3 0 INPUTS, others to OUTPUT
ANSEL =  %00000100      'Set AN2 , Fosc/32
ADCON0 = %00000000      'AN2 select & Right Justify for 10-bit
;---------------------------------------------------------------------------   
THROTTLE    VAR GPIO.0  'Outputs to throttle servo 
RADIO       VAR GPIO.1  'Input from receiver
LED         var GPIO.2  'status indicator
ADC_DATA	var	GPIO.3	' adc serial data
ADC_SCLK    var	GPIO.5	' adc serial clock
ADC_CS		var	GPIO.4	' adc chip select
;--------------------------------------------------------------------------- 
                       
advalue 	var	word    ' value read from adc
groundALT   var word
difalt      var word
P           VAR WORD    ' This stores the PULSIN value
x           var byte    ' general var
y           var byte    ' general var
SEC_COUNT   VAR BYTE    ' seconds counter
O_FLOWS     VAR BYTE    ' holds the number of timer1 overflows
BRAKE_PULSE var word    ' servo pulse to STOP (brake on) THR servo
BRAKE_PULSE = 100

'-= vars for averaging routine =-
AvgCount	CON  6		' = Number of samples to average
FAspread	CON  1000	' = Fast Average threshold +/-
Value		VAR  WORD
'-= end of vars for averaging routine =-

'******************************************************************************
' TIMER1 Cycle MUST be longer than a R/C frame duration to be sure not to miss any ticks.
' 50 ms is a good value for timing precision.
' PL = 15543 @ 4Mhz ( reload = 7 cycle )
'******************************************************************************

T1LO CON $49            'timer1 preload values
T1HI CON $C3            '$C349 -> -15543
low throttle

   INTCON  = 0          ' disable interrupts
   T1CON = %00010000    ' 1:2 prescale (1uS per tick), timer1 off (max 1:8!)
                        ' 11 = 1:8 ,10 = 1:4, 01 = 1:2, 00 = 1:1 Prescale Value
   TMR1H = T1HI         ' 65,536-15536 = 50.000
   TMR1L = T1LO         ' 50.000 ticks * 1uS =50.000usec.=100msec
                        ' 1 second= 100*10
                        ' every 10 timer1 overflows = 1 second   1uS=
'---------------------------------------------------------------------------
pause 3000

for x=1 to 4
	high led
	pause 200
	low led
	pause 100
next x



'******************************************************************************
CAL_BP: ' CALIBRATING Brake_Pulse ( P )
'******************************************************************************

	Pause 50
	LOW led
 	P = 0
 
	For x = 1 TO 16

		PulsIn radio,1,P
		
		IF ( P < 80 ) OR ( P > 220 ) Then
			Led = 1
			GoTo CAL_BP
		EndIF
		
	
		IF P = $00 Then prems
	
		IF ( P < (Brake_Pulse -1)) OR ( P > (Brake_Pulse +1)) THEN
			Led = 1
			GoTo CAL_BP
		ENDIF

prems:	Brake_Pulse = P
	
	Next x

LOW Throttle

''******************************************************************************
'calibrate:             'check for valid signal
'
'For x = 1 TO 2
'
'	PulsIn radio,1,P
'	pauseus 10
'	IF ( P < 80 ) OR ( P > 200 ) Then calibrate
'	next x
'	
'for x=1 to 3
'	PulsIn radio,1,P
'	brake_pulse = P
'next x
'
'low led
'
'low throttle

'*****************************************************************************
precheck:            'leave some seconds to do a motor test
						'then motor brake is ON for some seconds
for y=1 to 3
         
	for x=1 to 255
		PULSIN RADIO,1,P
				
		IF ( P < 80 ) OR ( P > 220 ) Then
			Led = 1
			GoTo Precheck
		EndIF
		
		Led = 0
		LOW Throttle            
		pULSOUT THROTTLE, p
		
	next x
	
next y

for x=1 to 160

	LOW Throttle
	PULSOUT THROTTLE, brake_pulse   
	pause 18
	
next x

low THROTTLE

GOSUB GetAdc         						'Get ground ALT
groundalt=value

'******************************************************************************
armcheck:									' Now, we can launch the beast ...
            
PULSIN RADIO,1,P            
	IF ( P < 80 ) OR ( P > 220 ) Then
		Led = 1								' Show Problem !!!		
		LOW Throttle
		GoTo Armcheck
	ENDIF
	
Led = 0		
low throttle
PULSOUT THROTTLE, p

if difalt < 2 OR difalt > 10000 then Armcheck 'Arm if>=5mALT (in adc samples) reached!!


'******************************************************************************
'******************************************************************************
start:                  				' We are flying , now ... preset timer1
 
   SEC_COUNT=28         				' load for 30 to 0 seconds countdown
   O_FLOWS=0            				' clear overflow count
   PIR1.0=0             				' clear timer1 overflow flag
   T1CON.0=1            				' start timer1
   
low throttle							' to be sure ...

'******************************************************************************
main:					
    
gosub GetADC

PULSIN RADIO,1,P            
pauseUS 10

pULSOUT THROTTLE, p

' Note: Timer1 overflows every 0.050 seconds

   IF PIR1.0 THEN           			' if timer1 overflow then
      O_FLOWS = O_FLOWS + 1     		' inc oveflow counter
      
      IF O_FLOWS = 20 THEN    			' if 1 second elapsed 
	      SEC_COUNT = SEC_COUNT - 1 	' decrement seconds count
	      O_FLOWS=0             		' reset overflow counter
      ENDIF
      
      PIR1.0=0              			' clear timer1 overflow flag
      T1CON.0 = 0           			' stop timer1
      
      TMR1H = T1HI 						' Reload values 
      TMR1L = T1LO

      T1CON.0=1              			' re-start timer1
     
   ENDIF
   
if difalt>=89 and difalt<10000 then KILL_MOTOR_ALT 'Check if 100mALT
                                                   '(in adc samples) reached!!
if sec_count<=0 then KILL_MOTOR_TMR

goto main


'                                SUBROUTINES
'******************************************************************************
'******************************************************************************
GetADC:									'Read MAX187 12bit ADC value

low ADC_CS
PAUSEUS 10 
shiftin ADC_DATA,ADC_SCLK,msbpost,[advalue\12]
high ADC_CS


Average:' -=-=-=-=-=-=  Average 6 X Analog values -=-=-=-=-=-=-=-=-=-=
    IF Value = advalue Then NoChange
    
    IF ABS (Value - advalue) > FAspread OR Value < AvgCount Then FastAvg
    IF ABS (Value - advalue) < AvgCount Then RealClose
    
    advalue = advalue - (advalue/AvgCount)
    advalue = advalue + (Value/AvgCount)
    GoTo AVGok
    
FastAvg:
    advalue = Value
    GoTo AVGok
    
RealClose:'If averaging more than 8 samples,change to (AvgCount/4)

    advalue = advalue - (advalue/(AvgCount/2)) 
    advalue = advalue + (Value/(AvgCount/2))
    
AVGok:
    Value = advalue					' Put Average back into Value
    
NoChange:' -=-=-=-=-=-=  End of Averageing -=-=-=-=-=-=-=-=-=-=

difalt=value-groundalt

return
END

'******************************************************************************   
KILL_MOTOR_ALT:
low throttle
high led

LOOP1:
PULSOUT throttle, brake_pulse   ; Kill motor - adjust this value. 4Mhz ->> 10uSec
pause 18                        
goto LOOP1

END
'******************************************************************************
KILL_MOTOR_TMR:
x = 0

LOOP2:

low throttle
PULSOUT throttle, brake_pulse   ; Kill motor - adjust this value. 4Mhz ->> 10uSec

IF X = 0  THEN led = led ^ 1
x = ( x+1 ) // 18							' Counter for led Blinking @ 1.5 Hz

pause 18                      
goto LOOP2

END
'******************************************************************************
'******************************************************************************

...

But did not try it ...

have fun

Alain

**ScaleRobotics** · - 19th January 2010, 17:52

Hey Bitmaniac,

You could try using a 20ms interrupt, and start your pulsout on interrupt. That would make things more consistent, and probably keep your motor controller happy.

**ScaleRobotics** · - 29th January 2010, 10:52

Hey Bitmaniac,

I was thinking this use of interrupts would probably keep things happy as far as motor controllers. It may need some more work though, and I still have to test it on a motor control.

http://www.picbasic.co.uk/forum/show...3834#post83834

Walter

**bitmaniac** · - 29th January 2010, 11:52

Well, Scalerobotics , Alain and others

May be we could give this aproach a try and see...

So let's sum up what I have tried so far:

1st just 12f683 -> 10bit ADC cannot do any MPX4115 useful calculations!

2nd 12f683 + LM358 op-amp for 'window-range' method -> clever idea but I think we may have erratic behavour as op-amp temp drift!

3rd 12f683 DT 14 bit oversampling method very good idea and increased resolution but delay issues with servo pass-through routines.

4th 12f683 + MAX187 12bit ADC (increased resolution-not as bad as internal 10bit and not as good as oversampling method) and interrupts for servo 'pass-trhough' LET's try it

Now I ended up in using a 12f683 internal osc (4MHz) + MAX187 so we have free interrupt sources and speed to try other methods.Also note that I have tried also with internal and external crystals and keep in-mind that I have already TMR1 running for the moment to keep track of 30sec. passing time.

Maybe I think somehow wrong / or weird for any of the above ideas ,please feel free to express your method / comments

Alain (Acetronics) some time ago , already gave a great idea for a completely different approach to the whole project, using an external DAC (NOT ADC!) to set the Vref of the pic internal 10bit adc so we 'narrow' the measurements of MPX to a resonable amount
This has also to be tried!!!

(P.S:For the moment I have a PIC ethernet project open.... in the same time)

**ScaleRobotics** · - 29th January 2010, 17:58

Originally Posted by bitmaniac

Also note that I have tried also with internal and external crystals and keep in-mind that I have already TMR1 running for the moment to keep track of 30sec. passing time.

Alain (Acetronics) some time ago , already gave a great idea for a completely different approach to the whole project, using an external DAC (NOT ADC!) to set the Vref of the pic internal 10bit adc so we 'narrow' the measurements of MPX to a resonable amount
This has also to be tried!!!

Hey Alexandros,

Certainly lots of methods to try. I am sure that Alain's method would work just fine. I just like the idea of interrupts, and using fewer components. And besides, I am learning a lot about interrupts and timers in the process, so that is good!

And for your 30 seconds: Since it is using a time base of 20ms on timer2, you could easily add a counter in that interrupt handler. And when it reached 1500, that is 30 seconds.

I will try adding the ADC oversample into it, and let you know how it goes. But my motor controller is taking kindly to it, and accepting it's pulses.

**bitmaniac** · - 31st January 2010, 16:40

Well a little bit of experiment with my last hardware : 12f683 , max187 12bit ADC , 4 Mhz Int osc. Servo attached instead of SC working ok (a little bit jerky -but acceptable) BUT when I connect SC it works only once at the begining when you plug the battery in.
So, after a little notice THE OBVIOUS THING CAME IN MY MIND!!

Of course there is a problem meanwhile with the SC , as soon as I 'break' for the first time just to to jump to my motor pre-check routine afterwards SC accepts no pulses at all for a period of time. So when I come back to re-activate the motor last position SC does not arm . It must go to arm procedure first (throttle low) and then it accepts signals!

So, the only way we can go is WITH interrupts just to keep the pulsout routine alive!

So obvious ......

**Acetronics2** · - 31st January 2010, 16:48

Hi, Alex

Interrupts ... ok, nice idea, ... but it will surely interfere with your INPUT Pulsin ....

hé,hé ... you said " Aaaargh !!! " ???

Alain

**ScaleRobotics** · - 31st January 2010, 17:48

Originally Posted by Acetronics

Interrupts ... ok, nice idea, ... but it will surely interfere with your INPUT Pulsin ....
Alain

If you go to interrupts, you will not need any pulsin, or pulsout. There are a couple ways to input multiple channels for pulse width measurement. You could either make an interrupt on change on GPIO port, then poll the pins for change, or ....

tie both outputs of the receiver together, and connect them to the CPP1 pin. Only one will pulse at a time (on most rc receivers), so you will be able to read one at a time, even though they are connected together.

One thing I am not sure about is if there is enough time between pulses to read adjacent channels. Have not tried that yet. But channels that are separated by one channel, like 1 and 3, etc would be easy. Hard part would be telling channels from each other. For this, you could place an input on one of the in between channels to mark which pulse width you would be measuring next.

Or, make a multiplexing switch that switches between the throttle, and the on/off switch, and have those go to the same CCP1 pin.

**Acetronics2** · - 31st January 2010, 17:53

Hi,

If you want to give a try ...

with " classical " receivers ( CMOS 4015/4017/HC164/NE5045 decoders ) you have ...

15 ns ... as a " mark pulse " ...

Alain

**bitmaniac** · - 1st February 2010, 06:51

... or maybe using HPWM for pulsout ? to keep SC alive all the time!

**Acetronics2** · - 2nd February 2010, 20:01

Hi, Alex

I spent some more time on your code ...

should work as I verified the timing and flow with MPSIM ...

Code:

'****************************************************************************
' (c)2009 Alexandros Zahariadis (E.A.TH.) Greece *
' Electric Glider electronic switch to be used in F3J-GR competitions.
' The device will cut-off motor if 200m ALT reached or 30seconds passed
' whichever comes first!
' There is also a status led option which idicates if you have reached 200m
' or not (may be because of luck of power!)
' steady led -> 200m ALT reached , blinking led -> 30 secs passed.
' NOTE: after a lot of experiments and because of code execution speed
' I use direct ADC raw sample values without converting them to meters first!
'    :: thanks to Acetronics (Alain) and picbasic forum for codding ideas ::
'****************************************************************************

'@ DEVICE FCMEN_OFF
'@ DEVICE IESO_OFF
'@ DEVICE BOD_ON
'@ DEVICE CPD_OFF
'@ DEVICE PROTECT_OFF
'@ DEVICE MCLR_OFF
'@ DEVICE PWRT_OFF
'@ DEVICE WDT_OFF
'@ DEVICE INTRC_OSC

@    __config _INTRC_OSC_NOCLKOUT & _WDT_ON & _PWRTE_ON & _MCLRE_OFF & _CP_OFF & _BOD_ON

INCLUDE "modedefs.bas"


DEFINE OSC 4
DEFINE PULSIN_MAX 2500

;DEFINE DEBUG_REG GPIO
;DEFINE DEBUG_BIT 2
;DEFINE DEBUG_BAUD 9600
;DEFINE DEBUG_MODE 1

OSCCON = $60            ' $60:4 Mhz $70:8 Mhz int.

CMCON0 = 7              'TURN COMPARATORS OFF
TRISIO = %00001010      'Set GPIO1 and GPIO3 0 INPUTS, others to OUTPUT
ANSEL =  %00000100      'Set AN2 , Fosc/32
ADCON0 = %00000000      'AN2 select & Right Justify for 10-bit

;---------------------------------------------------------------------------
'
THROTTLE    VAR GPIO.0  'Outputs to throttle servo 
RADIO       VAR GPIO.1  'Input from receiver
LED         VAR GPIO.2  'status indicator
ADC_DATA	VAR	GPIO.3	' adc serial data
ADC_SCLK    VAR	GPIO.5	' adc serial clock
ADC_CS		VAR	GPIO.4	' adc chip select

;--------------------------------------------------------------------------- 
                       
advalue 	VAR	word    ' value read from adc
groundALT   VAR word
difalt      VAR word
P           VAR WORD    ' This stores the PULSIN value
x           VAR byte    ' general var
y           VAR byte    ' general var
Dummy       VAR word
SEC_COUNT   VAR BYTE    ' seconds counter
O_FLOWS     VAR BYTE    ' holds the number of timer1 overflows
BRAKE_PULSE VAR word    ' servo pulse to STOP (brake on) THR servo

CLEAR

'BRAKE_PULSE = 100

'-= vars for averaging routine =-
AvgCount	CON  6		' = Number of samples to average
FAspread	CON  1000	' = Fast Average threshold +/-
Value		VAR  WORD
'-= end of vars for averaging routine =-

'******************************************************************************
' TIMER1 Cycle MUST be longer than a R/C frame duration to be sure not to miss any ticks.
' 50 ms is a good value for timing precision.
' PL = 15543 @ 4Mhz ( reload = 7 cycle )
'******************************************************************************

T1LO CON $49            'timer1 preload values
T1HI CON $C3            '$C349 -> -15543

LOW throttle

   INTCON  = 0          ' disable interrupts
   T1CON = %00010000    ' 1:2 prescale (1uS per tick), timer1 off (max 1:8!)
                        ' 11 = 1:8 ,10 = 1:4, 01 = 1:2, 00 = 1:1 Prescale Value
   TMR1H = T1HI         ' 65,536-15536 = 50.000
   TMR1L = T1LO         ' 50.000 ticks * 1uS =50.000usec.=100msec
                        ' 1 second= 100*10
                        ' every 10 timer1 overflows = 1 second   1uS=
'---------------------------------------------------------------------------
pause 3'000

for x=1 to 4
	high led
	pause 2'00
	low led
	pause 1'00
next x



'******************************************************************************
CAL_BP: ' CALIBRATING Brake_Pulse ( P )
		' Controller must see Brake Pulse to Unlock ...
'******************************************************************************

	Pause 50
	LOW led
 	Brake_Pulse = 0
 
	For x = 1 TO 16

		PULSIN radio,1,P
		
		IF ( P < 80 ) OR ( P > 220 ) Then
			Led = 1
			GoTo CAL_BP
		EndIF
		
	
		IF Brake_Pulse = $00 Then prems
	
		IF ( P < (Brake_Pulse -1)) OR ( P > (Brake_Pulse +1)) THEN
			Led = 1
			GoTo CAL_BP
		ENDIF

prems:	Brake_Pulse = P
	
	Next x

LOW Throttle

'*****************************************************************************
precheck:            'leave some seconds to do a motor test
					 'then motor brake is ON for some seconds
					 
for y=1 to 3
         
	for x=1 to 255
		PULSIN RADIO,1,P
				
		IF ( P < 80 ) OR ( P > 220 ) Then
			Led = 1
			GoTo Precheck
		EndIF
		
		Led = 0
		LOW Throttle            
		PULSOUT THROTTLE, p
		
	next x
	
next y

'******************************************************************************
' GroundAlt measure : Motor is Locked, But Brake_Pulse lenght must be sent ...
'******************************************************************************

for x=1 to 160								'160 x 22ms = 

	LOW Throttle
	PULSOUT THROTTLE, brake_pulse   
	pause 19
	
next x

low THROTTLE

GOSUB GetAdc         						'Get ground ALT
groundalt = value

'******************************************************************************
armcheck: '20.9 ms						' Now, we can launch the beast ...
            
PULSIN RADIO,1,P            
	IF ( P < 80 ) OR ( P > 220 ) Then
		Led = 1								' Show Problem !!!		
		LOW Throttle
		PULSOUT THROTTLE, brake_pulse		' Not to lock Controller
		GoTo Armcheck
	ENDIF
	
Led = 0		
low throttle
PULSOUT THROTTLE, p

GOSUB GetAdc         						'Get ALT

if difalt < 2 OR difalt > 10000 then Armcheck 'Arm if>=5mALT (in adc samples) reached!!


'******************************************************************************
'******************************************************************************
start:                  				' We are flying , now ... preset timer1
 
   SEC_COUNT=28         				' load for 30 to 0 seconds countdown
   O_FLOWS=0            				' clear overflow count
   PIR1.0=0             				' clear timer1 overflow flag
   T1CON.0=1            				' start timer1
   
low throttle							' to be sure ...

'******************************************************************************
main:					
    
gosub GetADC

PULSIN RADIO,1,P            
pauseUS 10

pULSOUT THROTTLE, p

' Note: Timer1 overflows every 0.050 seconds

   IF PIR1.0 THEN           			' if timer1 overflow then
      O_FLOWS = O_FLOWS + 1     		' inc oveflow counter
      
      IF O_FLOWS = 20 THEN    			' if 1 second elapsed 
	      SEC_COUNT = SEC_COUNT - 1 	' decrement seconds count
	      O_FLOWS=0             		' reset overflow counter
      ENDIF
      
      PIR1.0=0              			' clear timer1 overflow flag
      T1CON.0 = 0           			' stop timer1
      
      TMR1H = T1HI 						' Reload values 
      TMR1L = T1LO

      T1CON.0=1              			' re-start timer1
     
   ENDIF
   
if difalt>=89 and difalt<10000 then KILL_MOTOR_ALT 'Check if 100mALT
                                                   '(in adc samples) reached!!
if sec_count < 1 then KILL_MOTOR_TMR

goto main


'                                SUBROUTINES


'******************************************************************************
'******************************************************************************
GetADC:	'Read MAX187 12bit ADC value - Take 9.25 ms

low ADC_CS
PAUSEUS 10 




Average:' -=-=-=-=-=-=  Average 16 X Analog values -=-=-=-=-=-=-=-=-=-=

  For x = 0 to 15			' 16 Samples MAXI !!!
  
  shiftin ADC_DATA,ADC_SCLK,msbpost,[advalue\12]	'337 µs
  
  value = value + advalue
  
  PAUSEUS 200
  
  NEXT x
  
  Value = Value / 16

	
difalt = groundalt - value

high ADC_CS

RETURN

END

'******************************************************************************

KILL_MOTOR_ALT:

low throttle
high led

LOOP1:
PULSOUT throttle, brake_pulse   ' Kill motor - adjust this value. 4Mhz ->> 10uSec
pause 19                        
goto LOOP1

END
'******************************************************************************

KILL_MOTOR_TMR:

x 		= 0
T1CON.0 = 0						' Stop the Timer			

LOOP2:

low throttle
PULSOUT throttle, brake_pulse   ' Kill motor - adjust this value. 4Mhz ->> 10uSec

IF X = 0  THEN led = led ^ 1
x = ( x+1 ) // 18							' Counter for led Blinking @ 1.5 Hz

pause 19                      
goto LOOP2

END
'******************************************************************************
'******************************************************************************

Fond some " strange " things and corrected them ...

Alain

**bitmaniac** · - 2nd February 2010, 20:55

(SO....I have to see both codes side by side so I can learn for my mistakes

)

You 've done excellent coding ...I'll give it a try although I had problems with averaging routines -keep sending '0' as result!

**Darrel Taylor** · - 2nd February 2010, 22:02

I agree with Walter.
All this "Software Timed" stuff just doesn't work well together.

Everything, should be Interrupt driven.

Capture (CCP) the received pulses.
Use A/D interrupt to OverSample the Altitude. (oversampling does not have to be "Blocking")
Timer interrupt to drive the servo.

No PULSIN's, no PULSOUT's, no SHIFTIN/OUT.

These PIC chips are extremely fast. (As long as the program isn't sitting in a loop somewhere waisting 90% of it's time.)
And with the Hardware doing most of the work, they "Scream".

Even if you don't use Interrupts ... Use the hardware.
<br>

**Acetronics2** · - 3rd February 2010, 09:32

Hi, Alex ...

just two little "bugs" of mine ...

Code:

'---------------------------------------------------------------------------
pause 3000

for x=1 to 4
	high led
	pause 200
	low led
	pause 100
next x

... I only forgot to clear the comments for shortening delays when using MPSIM ...

Here is the good sequence ...

AND

Code:

Average:' -=-=-=-=-=-=  Average 16 X Analog values -=-=-=-=-=-=-=-=-=-=

Value = 0

  For x = 0 to 15			' 16 Samples MAXI !!!
  
  shiftin ADC_DATA,ADC_SCLK,msbpost,[advalue\12]	'337 µs
  
  value = value + advalue

Forgot resetting "value" ... Boooo.

But ... you of course had noticed it !

Alain

PS for Darrel ...

Everything, should be Interrupt driven.

You really sure ??? ... not me, here for R/C Gadgets ...

**flotulopex** · - 3rd June 2010, 06:48

Hi All,

Just a question about DEFINEs.

In Darrel's code, I can see

Code:

DEFINE ADC_BITS 16 '10 BIT A/D CONVERSION RESULT

What does it mean?

I'm using a 12F683 that can only do a 10 bits resolution son what do I not understand? Why 16?

**bitmaniac** · - 3rd June 2010, 07:41

Originally Posted by flotulopex

Hi All,
....
I'm using a 12F683 that can only do a 10 bits resolution son what do I not understand? Why 16?

Well my friend if you read carefully you would notice that Darell uses a method called 'Oversampling technique' to increase the resolution by software trick.
more info at : http://www.darreltaylor.com/DT_Analog/

So the actual hardware used is the onboard f683 10bit but with 'oversampling' by software you can archive 16 bit resolution result with speed penalty as a drawback.
By using define you can use 10 to 16 bit 'sampling' with the most common use be the 12 bit sampling as a matter of speed.

Have a nice day my friend!

**flotulopex** · - 3rd June 2010, 09:13

Thanks bitmaniac,

I have read Alain's explanation about "oversampling" and "rolling mean value" in a previous post but I'm still not clear why it is necessary to declare a DEFINE to do so.

I think, I don't understand what the DEFINE does.

Any clue for me?

**mark_s** · - 3rd June 2010, 15:37

Originally Posted by flotulopex

Thanks bitmaniac,

I have read Alain's explanation about "oversampling" and "rolling mean value" in a previous post but I'm still not clear why it is necessary to declare a DEFINE to do so.

I think, I don't understand what the DEFINE does.

Any clue for me?

Hello,
You are correct you should set the pic to 10 bits:
DEFINE ADC_BITS 10

http://www.darreltaylor.com/DT_Analog/

If you study Darrel's example in the above link, bottom of the article.
You set your oversampling resolution in this line:

ADbits = 12 ; set to 12-bit resolution

Regards
Mark

**Acetronics2** · - 3rd June 2010, 16:41

Originally Posted by flotulopex

I think, I don't understand what the DEFINE does.

Any clue for me?

Hello, Roger

DEFINE only set a constant ... used to DEFINE some processor module or macros configs.

the value is tested, and relevant settings are chosen by the compiler ( sort of conditionnal assembly - if you prefer ... sort of !!! )

just look at the difference ( in the asm listing) between DEFINE ADC_BITS 8 and ADC_BITS 10 ...

Should be little differences in the ADCONx setting values ... don't you think ???

Alain

**flotulopex** · - 3rd June 2010, 21:34

Thanks Alain,

I was confused because of the value (16) in Darrel's code example.

I now understand what this particular DEFINE does

**flotulopex** · - 3rd March 2011, 09:44

Hi Darrel,

I'm a little confused about how to convert the ADC "pressure" result in an altitude (from 0.2V...4.8V to n meters or feets).

I've read lots of posts, but it is still unclear to me

**Darrel Taylor** · - 3rd March 2011, 15:04

Hi Roger,

Me too.
All I did was convert to kPa, PSI or BAR as shown in this calculator.
http://www.pbpgroup.com/Calculators/...A/MPX4115A.htm

Walter did a project for an altimeter using a lookup table ...
http://www.picbasic.co.uk/forum/cont...-picbasic-code

.

**ScaleRobotics** · - 3rd March 2011, 17:25

I need to work at this a little to explain it well. But here is a shot at explaining it generally. I am still looking for the excel spreadsheet I did to make my lookup table ... but in the mean time...

Using an excel spread sheet, put a formula for calculating altitude from pressure. Add the formula for your pressure sensor to convert its voltage to pressure. Add in the part that converts your A/D reading to a voltage. Once you get to a point where you can say a reading of xxx of your a/d conversion gives you x feet or meters, you can find some evenly spaced a/d readings, and input the corresponding feet or meters into a lookup table. I know this explanation kind of stinks, because you need some examples here. I will try to elaborate on this later.

Anyway, once you have your lookup table, you need to divide your a/d reading by a number. If you look at my lookup table, you see that I am dividing by 1000 and subtracting 15. This is for a 16 bit A/D result. (In my code, even if you decide to use 12 bit resolution, it is shifted up to 16 bits so it can use the same lookup table). The subtract 15 lets you lower the start of your max altitude. Normal folks might just want to go up to 12,000 feet, or maybe even lower, so they would have a bigger subtraction number, and a different lookup table, that started at a lower altitude.

You may notice that I am looking up two values. This is because the value from the adc will be between two of the lookup table values. The lookup values in my table are about 400 feet or so apart. To make this somewhat accurate, we need to lookup both readings in the lookup table, find the difference in feet, then take our remainder from divide by 1000 and multiply the fraction to the difference in feet. Then I subtract this from my TempAlt to get a final altitude. For this to work, my lookup table had to be made at Analog to digital steps of 1000. That makes the math a little easier.

I am pretty sure I used Alain's spreadsheet as a base to calculate my lookup table. You can find his spreadsheet in Post 33 and another one of his previous. Also BitManiac has a spreadsheet in there as well. Here are my values, calculating for even 1000 steps for the A/D value. Table step number is shown, as is feet of altitude, and pressure in Pa.

<table frame="VOID" rules="NONE" border="0" cellspacing="0" cols="4"> <colgroup><col width="83"><col width="93"><col width="107"><col width="107"></colgroup> <tbody> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20" width="83">A/D Value</td> <td align="CENTER" bgcolor="#E6E6E6" width="93">Table step </td> <td align="CENTER" bgcolor="#E6E6E6" width="107">Feet</td> <td align="CENTER" bgcolor="#E6E6E6" width="107">Pa</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">54000</td> <td align="CENTER" bgcolor="#E6E6E6">39</td> <td align="CENTER" bgcolor="#E6E6E6">-237</td> <td align="CENTER" bgcolor="#E6E6E6">102.2</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">53000</td> <td align="CENTER" bgcolor="#E6E6E6">38</td> <td align="CENTER" bgcolor="#E6E6E6">226</td> <td align="CENTER" bgcolor="#E6E6E6">100.5</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">52000</td> <td align="CENTER" bgcolor="#E6E6E6">37</td> <td align="CENTER" bgcolor="#E6E6E6">696</td> <td align="CENTER" bgcolor="#E6E6E6">98.8</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">51000</td> <td align="CENTER" bgcolor="#E6E6E6">36</td> <td align="CENTER" bgcolor="#E6E6E6">1172</td> <td align="CENTER" bgcolor="#E6E6E6">97.11</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">50000</td> <td align="CENTER" bgcolor="#E6E6E6">35</td> <td align="CENTER" bgcolor="#E6E6E6">1655</td> <td align="CENTER" bgcolor="#E6E6E6">95.41</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">49000</td> <td align="CENTER" bgcolor="#E6E6E6">34</td> <td align="CENTER" bgcolor="#E6E6E6">2145</td> <td align="CENTER" bgcolor="#E6E6E6">93.71</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">48000</td> <td align="CENTER" bgcolor="#E6E6E6">33</td> <td align="CENTER" bgcolor="#E6E6E6">2643</td> <td align="CENTER" bgcolor="#E6E6E6">92.02</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">47000</td> <td align="CENTER" bgcolor="#E6E6E6">32</td> <td align="CENTER" bgcolor="#E6E6E6">3148</td> <td align="CENTER" bgcolor="#E6E6E6">90.32</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">46000</td> <td align="CENTER" bgcolor="#E6E6E6">31</td> <td align="CENTER" bgcolor="#E6E6E6">3660</td> <td align="CENTER" bgcolor="#E6E6E6">88.62</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">45000</td> <td align="CENTER" bgcolor="#E6E6E6">30</td> <td align="CENTER" bgcolor="#E6E6E6">4181</td> <td align="CENTER" bgcolor="#E6E6E6">86.92</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">44000</td> <td align="CENTER" bgcolor="#E6E6E6">29</td> <td align="CENTER" bgcolor="#E6E6E6">4710</td> <td align="CENTER" bgcolor="#E6E6E6">85.23</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">43000</td> <td align="CENTER" bgcolor="#E6E6E6">28</td> <td align="CENTER" bgcolor="#E6E6E6">5247</td> <td align="CENTER" bgcolor="#E6E6E6">83.53</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">42000</td> <td align="CENTER" bgcolor="#E6E6E6">27</td> <td align="CENTER" bgcolor="#E6E6E6">5794</td> <td align="CENTER" bgcolor="#E6E6E6">81.83</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">41000</td> <td align="CENTER" bgcolor="#E6E6E6">26</td> <td align="CENTER" bgcolor="#E6E6E6">6349</td> <td align="CENTER" bgcolor="#E6E6E6">80.14</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">40000</td> <td align="CENTER" bgcolor="#E6E6E6">25</td> <td align="CENTER" bgcolor="#E6E6E6">6915</td> <td align="CENTER" bgcolor="#E6E6E6">78.44</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">39000</td> <td align="CENTER" bgcolor="#E6E6E6">24</td> <td align="CENTER" bgcolor="#E6E6E6">7490</td> <td align="CENTER" bgcolor="#E6E6E6">76.74</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">38000</td> <td align="CENTER" bgcolor="#E6E6E6">23</td> <td align="CENTER" bgcolor="#E6E6E6">8076</td> <td align="CENTER" bgcolor="#E6E6E6">75.04</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">37000</td> <td align="CENTER" bgcolor="#E6E6E6">22</td> <td align="CENTER" bgcolor="#E6E6E6">8672</td> <td align="CENTER" bgcolor="#E6E6E6">73.35</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">36000</td> <td align="CENTER" bgcolor="#E6E6E6">21</td> <td align="CENTER" bgcolor="#E6E6E6">9280</td> <td align="CENTER" bgcolor="#E6E6E6">71.65</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">35000</td> <td align="CENTER" bgcolor="#E6E6E6">20</td> <td align="CENTER" bgcolor="#E6E6E6">9900</td> <td align="CENTER" bgcolor="#E6E6E6">69.95</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">34000</td> <td align="CENTER" bgcolor="#E6E6E6">19</td> <td align="CENTER" bgcolor="#E6E6E6">10532</td> <td align="CENTER" bgcolor="#E6E6E6">68.26</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">33000</td> <td align="CENTER" bgcolor="#E6E6E6">18</td> <td align="CENTER" bgcolor="#E6E6E6">11176</td> <td align="CENTER" bgcolor="#E6E6E6">66.56</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">32000</td> <td align="CENTER" bgcolor="#E6E6E6">17</td> <td align="CENTER" bgcolor="#E6E6E6">11834</td> <td align="CENTER" bgcolor="#E6E6E6">64.86</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">31000</td> <td align="CENTER" bgcolor="#E6E6E6">16</td> <td align="CENTER" bgcolor="#E6E6E6">12507</td> <td align="CENTER" bgcolor="#E6E6E6">63.16</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">30000</td> <td align="CENTER" bgcolor="#E6E6E6">15</td> <td align="CENTER" bgcolor="#E6E6E6">13194</td> <td align="CENTER" bgcolor="#E6E6E6">61.47</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">29000</td> <td align="CENTER" bgcolor="#E6E6E6">14</td> <td align="CENTER" bgcolor="#E6E6E6">13896</td> <td align="CENTER" bgcolor="#E6E6E6">59.77</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">28000</td> <td align="CENTER" bgcolor="#E6E6E6">13</td> <td align="CENTER" bgcolor="#E6E6E6">14615</td> <td align="CENTER" bgcolor="#E6E6E6">58.07</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">27000</td> <td align="CENTER" bgcolor="#E6E6E6">12</td> <td align="CENTER" bgcolor="#E6E6E6">15351</td> <td align="CENTER" bgcolor="#E6E6E6">56.38</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">26000</td> <td align="CENTER" bgcolor="#E6E6E6">11</td> <td align="CENTER" bgcolor="#E6E6E6">16106</td> <td align="CENTER" bgcolor="#E6E6E6">54.68</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">25000</td> <td align="CENTER" bgcolor="#E6E6E6">10</td> <td align="CENTER" bgcolor="#E6E6E6">16879</td> <td align="CENTER" bgcolor="#E6E6E6">52.98</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">24000</td> <td align="CENTER" bgcolor="#E6E6E6">9</td> <td align="CENTER" bgcolor="#E6E6E6">17673</td> <td align="CENTER" bgcolor="#E6E6E6">51.29</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">23000</td> <td align="CENTER" bgcolor="#E6E6E6">8</td> <td align="CENTER" bgcolor="#E6E6E6">18489</td> <td align="CENTER" bgcolor="#E6E6E6">49.59</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">22000</td> <td align="CENTER" bgcolor="#E6E6E6">7</td> <td align="CENTER" bgcolor="#E6E6E6">19327</td> <td align="CENTER" bgcolor="#E6E6E6">47.89</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">21000</td> <td align="CENTER" bgcolor="#E6E6E6">6</td> <td align="CENTER" bgcolor="#E6E6E6">20190</td> <td align="CENTER" bgcolor="#E6E6E6">46.19</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">20000</td> <td align="CENTER" bgcolor="#E6E6E6">5</td> <td align="CENTER" bgcolor="#E6E6E6">21078</td> <td align="CENTER" bgcolor="#E6E6E6">44.5</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">19000</td> <td align="CENTER" bgcolor="#E6E6E6">4</td> <td align="CENTER" bgcolor="#E6E6E6">21995</td> <td align="CENTER" bgcolor="#E6E6E6">42.8</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">18000</td> <td align="CENTER" bgcolor="#E6E6E6">3</td> <td align="CENTER" bgcolor="#E6E6E6">22942</td> <td align="CENTER" bgcolor="#E6E6E6">41.1</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">17000</td> <td align="CENTER" bgcolor="#E6E6E6">2</td> <td align="CENTER" bgcolor="#E6E6E6">23921</td> <td align="CENTER" bgcolor="#E6E6E6">39.41</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">16000</td> <td align="CENTER" bgcolor="#E6E6E6">1</td> <td align="CENTER" bgcolor="#E6E6E6">24934</td> <td align="CENTER" bgcolor="#E6E6E6">37.71</td> </tr> <tr> <td align="CENTER" bgcolor="#E6E6E6" height="20">15000</td> <td align="CENTER" bgcolor="#E6E6E6">0</td> <td align="CENTER" bgcolor="#E6E6E6">25985</td> <td align="CENTER" bgcolor="#E6E6E6">36.01</td> </tr> </tbody> </table>

I have attached one interesting pdf. It is not the formula I used for my lookup table, but it is interesting.

Walter

Thread: MPXA4115A picbasic code

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digital oscilosope may will clear things out!

maybe interrupt is the way to go

"define adc_bits 16" ???

Why "DEFINE" ?

ok

pressure to altitude conversion formula

Re: MPXA4115A picbasic code

Re: MPXA4115A picbasic code

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