PIC16F84A Tachometer LED routine

**ThaSanta** · - 18th October 2008, 23:29

I'm writing a routine to a tachometer. I just doesn't work! I've searched the forum, but i haven't found anything that looks like this.

Code:

'****************************************************************
'*  Name    : Tacho.BAS                                         *
'*  Author  : Christian Lerche                                  *
'*  Notice  : Copyright (c) 2008 Lerche                         *
'*          : All Rights Reserved                               *
'*  Date    : 07-10-2008                                        *
'*  Version : 1.0                                               *
'*  Notes   : PIC16F84A @ 10 Mhz XT                             *
'*          : XT osc, BODEN off, WD off                         *
'****************************************************************
'Include------------------------------------------------------------------------

'Definitions--------------------------------------------------------------------                                     
Define osc 10                          ' Define Osc as 10 Mhz
DEFINE PULSIN_MAX 25000                ' Lowest RPM 600

'Inputs/outputs-----------------------------------------------------------------
TRISB = $80                            ' All PortB Output
TRISA = $f0                            ' All PortA Output
INPUT PORTA.4                          ' PortA.4 Input

'Variables----------------------------------------------------------------------
B0 VAR BYTE                            ' Define B0 as byte
W1 var WORD                            ' Define W1 as word
     
'Main program-------------------------------------------------------------------                                       
loop:      
        IF PORTA.4 THEN                ' Wait until start of low pulse
                GOTO MAIN1
            ELSE
                GOTO loop
        ENDIF 
MAIN1:
        PULSIN PORTA.4,0,W1            ' Measure pulse-width in 4µS resolution
        GOTO MAIN
MAIN:
        W1 = W1 * 4                    ' Convert µS to mS
        W1 = (60000 / W1)              ' Revs in 60 mS
        W1 = W1 * 1000                 ' Revs in 60 sec
            GOSUB display              ' Go to display sobroutine       
        GoTo LOOP                      ' Do forever
        
'Display subroutine------------------------------------------------------------- 
display: B0 = W1 / 1000	               ' Find number of thousands
	W1 = W1 // 1000	                   ' Remove thousands from W1
	   Gosub bin2seg	               ' Convert number to segments
	PortB = B0	                       ' Send segments to LED
	PortA = $17	                       ' Turn on fourth digit
	Pause 1    		                   ' Leave it on 1 ms
	PortA = $1F	                       ' Turn off digit to prevent ghosting 
	B0 = W1 / 100	                   ' Find number of hundreds
	W1 = W1 // 100	                   ' Remove hundreds from W1
	   Gosub bin2seg	               ' Convert number to segments
	PortB = B0	                       ' Send segments to LED
	PortA = $1B	                       ' Turn on third digit
	Pause 1    	                       ' Leave it on 1 ms
	PortA = $1F	                       ' Turn off digit to prevent ghosting 
	B0 = W1 / 10	                   ' Find number of tens
	W1 = W1 // 10	                   ' Remove tens from W1
	   Gosub bin2seg	               ' Convert number to segments
	PortB = B0	                       ' Send segments to LED
	PortA = $1D	                       ' Turn on second digit
	Pause 1    	                       ' Leave it on 1 ms
	PortA = $1F	                       ' Turn off digit to prevent ghosting 
	B0 = W1		                       ' Get number of ones
	   Gosub bin2seg	               ' Convert number to segments
	PortB = B0	                       ' Send segments to LED
	PortA = $1E	                       ' Turn on first digit
	Pause 1    	                       ' Leave it on 1 ms
	PortA = $1F	                       ' Turn off digit to prevent ghosting
    Return		                       ' Return to main
                                       ' Routine copied from ledart.

'Lookup table-------------------------------------------------------------------
bin2seg:
    Lookup B0,[$40,$79,$24,$30,$19,$12,$02,$78,$00,$18],B0
	Return

Anyone got a clue, what is does wrong?

Thanks in advance!

/ ThaSanta

**mackrackit** · - 19th October 2008, 02:33

What part does not work?

**Acetronics2** · - 19th October 2008, 09:43

Hi, Santa ( de bois )

1) Just the usual gag with PORTA.4 ...

Did you place an external pullup resistor or something to drive the pin to HIGH state ???

2) I note 10 Mhz need a HS Osc ... ( but generally works with XT !!! )

3)

Code:

MAIN1:
        PULSIN PORTA.4,0,W1            ' Measure pulse-width in 4µS resolution
        GOTO MAIN

you'd better try

Code:

MAIN1:
        RCTIME PORTA.4,0,W1            ' Measure pulse-width in 4µS resolution
        GOTO MAIN

4) your Mathematics are really bad for INTEGERS using ...

W1 = W1 * 4 ' Convert µS to mS
W1 = (60000 / W1) ' Revs in 60 mS
W1 = W1 * 1000 ' Revs in 60 sec

you'd much better use DIV32 ...

That's the first hits ...

Alain

**ThaSanta** · - 19th October 2008, 15:58

Sorry for letting the problem out (I was kinda tired).

The attached image views the first digit of 4. As if the algorithm doesn't calculate the RPM correct.

1) - I have not yet build the circuit, as I don't have a programmer.
2) - I don't think the Simulator cares about HS or XT :-)

3) I wrote RCTIME instead of PULSIN, but it didn't chance anything.

Actually, after reading the manual to PBP, i don't know how to use DIV32.
I've tried examples, but I still can't figure it out.

- Thanks again guys. :-)

**Acetronics2** · - 19th October 2008, 17:25

Hi,

The most annoying thing in your project is ... the PIC must drive continuously the 4 digits AND while that, must measure the rotation period.

I think you'll quickly understand you'll have to use interrupts and ... a 16Bits timer ... what the 16F84 doesn't have aboard ...
so, you'll also have to watch for TMR0 overflows ...to increment a 8 bits counter for the timer Upper 8 bits counting.

Not really easy ( "asm" recommended here )... but doable.

seeing your pain for the first steps ... I'd recommend you to switch to a 16F628a that has everything to EASILY realise such a RPM meter. ( I mean the capture module ... )

The project is yours ... you are the one who decides !!!

Alain

skimask · - 19th October 2008, 18:13

Originally Posted by Acetronics

Hi, Santa ( de bois )
1) Just the usual gag with PORTA.4 ...
Did you place an external pullup resistor or something to drive the pin to HIGH state ???

Only applies when using PortA.4 as an output...

Originally Posted by ThaSanta

2) - I don't think the Simulator cares about HS or XT :-)

Arg! Simulators!

**ThaSanta** · - 19th October 2008, 20:47

I think you'll quickly understand you'll have to use interrupts and ... a 16Bits timer ... what the 16F84 doesn't have aboard ...
so, you'll also have to watch for TMR0 overflows ...to increment a 8 bits counter for the timer Upper 8 bits counting.

I'll go along and try to use the CCP on Pic16F628A :-)
I'll be back with updates.

Thanks for the fast replies!

**Archangel** · - 19th October 2008, 23:53

edit:all good . . .

skimask · - 19th October 2008, 23:51

Here's one small problem...

Code:

Define osc 10                          ' Define Osc as 10 Mhz

http://www.picbasic.co.uk/forum/showthread.php?t=558

**ThaSanta** · - 20th October 2008, 00:20

I really think somethings wrong with the math. I just can't figure it out :/

Now an example:

Code:

MAIN:
        W1 = W1 * 2                    ' To get whole period
        W1 = W1 * 4                    ' now the count is in mS
        W1 = (60000/W1)                ' Revs per 60 mS
        W1 = W1 * 1000                 ' Revs per minute
            GOSUB display              ' Go to display sobroutine       
        GoTo LOOP                      ' Do forever

The input has a period of 12 mS (5000 RPM) - Which is 1500 increments @ 4µS.
As I only measure the low part of the 50% duty-cycle, I multiply with 2. Full period.
Then I multiply with 4. Now it's in mS. 12,000.
60,000 / 12,000 = 5.
5 * 1000 = 5000 RPM. NICE! - But i doesn't work.

I have seriously no idea of why this shouldn't work.

EDIT:
And then i thought. Figure out when i goes wrong:
So i tried to make the calculations. With a number, that wouldn't go straight up into 60,000. Example: 2000.
2,000*2=4,000
4,000*4=16,000
60,000/16,000=3.75 <- I guess this is were the PIC can't follow my lead.
3.75*1,000= 3750.

skimask · - 20th October 2008, 01:18

Originally Posted by ThaSanta

EDIT:
And then i thought. Figure out when i goes wrong:
So i tried to make the calculations. With a number, that wouldn't go straight up into 60,000. Example: 2000.
2,000*2=4,000
4,000*4=16,000
60,000/16,000=3.75 <- I guess this is were the PIC can't follow my lead.
3.75*1,000= 3750.

Well, since PicBasicPro (nor the PIC itself) doesn't support floating point variables, it's not surprising...

**Andy Wood** · - 20th October 2008, 02:47

Originally Posted by ThaSanta

I'm writing a routine to a tachometer. I just doesn't work! I've searched the forum, but i haven't found anything that looks like this.

Code:

'****************************************************************
'*  Name    : Tacho.BAS                                         *
'*  Author  : Christian Lerche                                  *
'*  Notice  : Copyright (c) 2008 Lerche                         *
'*          : All Rights Reserved                               *
'*  Date    : 07-10-2008                                        *
'*  Version : 1.0                                               *
'*  Notes   : PIC16F84A @ 10 Mhz XT                             *
'*          : XT osc, BODEN off, WD off                         *
'****************************************************************
'Include------------------------------------------------------------------------

'Definitions--------------------------------------------------------------------                                     
Define osc 10                          ' Define Osc as 10 Mhz
DEFINE PULSIN_MAX 25000                ' Lowest RPM 600

'Inputs/outputs-----------------------------------------------------------------
TRISB = $80                            ' All PortB Output
TRISA = $f0                            ' All PortA Output
INPUT PORTA.4                          ' PortA.4 Input

'Variables----------------------------------------------------------------------
B0 VAR BYTE                            ' Define B0 as byte
W1 var WORD                            ' Define W1 as word
     
'Main program-------------------------------------------------------------------                                       
loop:      
        IF PORTA.4 THEN                ' Wait until start of low pulse
                GOTO MAIN1
            ELSE
                GOTO loop
        ENDIF 
MAIN1:
        PULSIN PORTA.4,0,W1            ' Measure pulse-width in 4µS resolution
        GOTO MAIN
MAIN:
        W1 = W1 * 4                    ' Convert µS to mS
        W1 = (60000 / W1)              ' Revs in 60 mS
        W1 = W1 * 1000                 ' Revs in 60 sec
            GOSUB display              ' Go to display sobroutine       
        GoTo LOOP                      ' Do forever
        
'Display subroutine------------------------------------------------------------- 
display: B0 = W1 / 1000	               ' Find number of thousands
	W1 = W1 // 1000	                   ' Remove thousands from W1
	   Gosub bin2seg	               ' Convert number to segments
	PortB = B0	                       ' Send segments to LED
	PortA = $17	                       ' Turn on fourth digit
	Pause 1    		                   ' Leave it on 1 ms
	PortA = $1F	                       ' Turn off digit to prevent ghosting 
	B0 = W1 / 100	                   ' Find number of hundreds
	W1 = W1 // 100	                   ' Remove hundreds from W1
	   Gosub bin2seg	               ' Convert number to segments
	PortB = B0	                       ' Send segments to LED
	PortA = $1B	                       ' Turn on third digit
	Pause 1    	                       ' Leave it on 1 ms
	PortA = $1F	                       ' Turn off digit to prevent ghosting 
	B0 = W1 / 10	                   ' Find number of tens
	W1 = W1 // 10	                   ' Remove tens from W1
	   Gosub bin2seg	               ' Convert number to segments
	PortB = B0	                       ' Send segments to LED
	PortA = $1D	                       ' Turn on second digit
	Pause 1    	                       ' Leave it on 1 ms
	PortA = $1F	                       ' Turn off digit to prevent ghosting 
	B0 = W1		                       ' Get number of ones
	   Gosub bin2seg	               ' Convert number to segments
	PortB = B0	                       ' Send segments to LED
	PortA = $1E	                       ' Turn on first digit
	Pause 1    	                       ' Leave it on 1 ms
	PortA = $1F	                       ' Turn off digit to prevent ghosting
    Return		                       ' Return to main
                                       ' Routine copied from ledart.

'Lookup table-------------------------------------------------------------------
bin2seg:
    Lookup B0,[$40,$79,$24,$30,$19,$12,$02,$78,$00,$18],B0
	Return

Anyone got a clue, what is does wrong?

Thanks in advance!

/ ThaSanta

Please check this line:

loop:
IF PORTA.4 THEN ' Wait until start of low pulse

Should it be:

IF PORTA.4 = 0 THEN ' Wait until start of low pulse

Andy

skimask · - 20th October 2008, 05:04

Originally Posted by Andy Wood

Please check this line:
loop:
IF PORTA.4 THEN ' Wait until start of low pulse
Should it be:
IF PORTA.4 = 0 THEN ' Wait until start of low pulse
Andy

Unless he's just making sure that the timing loop doesn't start in the middle of the pulse...

**ThaSanta** · - 20th October 2008, 10:01

Originally Posted by Andy Wood

Please check this line:

loop:
IF PORTA.4 THEN ' Wait until start of low pulse

Should it be:

IF PORTA.4 = 0 THEN ' Wait until start of low pulse

Andy

- As Skimask says: I am making sure it is not starting from the middle of a period

**Acetronics2** · - 20th October 2008, 10:06

Hi Christian,

I'd like to be sure of one thing : what do you use as a rotation detector ???

... as in your calculations, the pulsin signal is supposed to be equal to the rotation period, something hurts me ... but what ???

Alain

**ThaSanta** · - 20th October 2008, 16:13

Originally Posted by Acetronics

Hi Christian,

I'd like to be sure of one thing : what do you use as a rotation detector ???

... as in your calculations, the pulsin signal is supposed to be equal to the rotation period, something hurts me ... but what ???

Alain

As it is, I am only using a simulator. I do not have a programmer.

Actually, it's supposed to measure the RPM of a computer-fan. 50% duty-cycle. :-)

**Dave** · - 21st October 2008, 11:45

ThaSanta, Here is a snipit of code I wrote about 4 years ago to do exactly what you are requesting..

ASM
PutMulResult macro Const32
MOVE?CB low Const32, R2
MOVE?CB low (Const32 >> 8), R2 + 1
MOVE?CB low (Const32 >> 16), R0
MOVE?CB low (Const32 >> 24), R0 + 1
endm
ENDASM

PULSIN B_IN,1,POINTER1 'MEASURE HIGH PULSE
IF POINTER1 > 0 THEN
@ PutMulResult 15000000 ' Load PBP internal vars Max= 2,147,483,648
POINTER2 = DIV32 POINTER1 ' Divide 15000000/(PERIOD/2)
SCRATCH = R2 ' Get remainder of Div32
' Change remainder to Decimals
SCRATCH = SCRATCH * 10000 ' Multiply remainder * 10,000
SCRATCH = DIV32 POINTER1 ' Divide remainder by original divisor
ELSE
POINTER2 = 0
SCRATCH = 0
ENDIF
LCDOUT $FE,LINE(1)
PAUSEUS 100
LCDOUT DEC5 POINTER2,".",DEC4 SCRATCH

I hope it works for you... It did for me...

Dave Purola,
N8NTA

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is the Pic the good one ??? ... not so sure.

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