Hello
Thanks for all the good tips and trick here it has helped me a lot. I think this is the right tread to put this.

I am making an analogue Amp Instrument with a Servo with an arrow that shows the +10 to -10 Amp. Its for an old style motorbike.

I have an Allegro Current Sensor, represented by Pot ASC714. The ASC714 Zero IN current give an output of 2.5V. I want the span to be between +10 Amps to -10 Amps. Each Amp out of the sensor =66mV. The output is:
+10A=3.16V=255
0A=2.5V=127
-10A=1.84V=0

I use only 8bit A/D and a PIC16F887.
I have set Vref+ to 3.16V and Vref- to 1.84V
At first sight it look that its working fine. But after some jogging with the pot it sometimes count up instead of down and vice versa. I think it has something with the Div32 to do and that i overflow it but cant figure out how to correct this.

Thankful for all solutions
Ole Thronborg


'************************************************* ***************
'* Name : Amp887.BAS *
'* Date : 17/3/2011 *
'* Notes : Read ASC714, Out LCD +-10A and move Servo *
'* Show value in bit and Amp on LCD display
'* For PIC16F887 *
'* For standard servo settings 1-2mS set LOW_servo con 100 *
'* and HIGH_servo CON 200 *
'************************************************* ***************
'Define OSC and ADC
DEFINE OSC 4 ' Set internal Oschillator to 4Mhz
DEFINE ADC_BITS 8 ' Set number of bits in result
DEFINE ADC_CLOCK 2 ' Set clock source (3=rc)
DEFINE ADC_SAMPLEUS 50 ' Set sampling time in uS

' Define LCD pins
Define LCD_DREG PORTD 'LCD data port
Define LCD_DBIT 0 'LCD data starting bit 0 or 4
Define LCD_RSREG PORTD 'LCD register select port
Define LCD_RSBIT 4 'LCD register select bit
Define LCD_EREG PORTD 'LCD enable port
Define LCD_EBIT 5 'LCD enable bit

TRISA = %00001101 ' RA0 = A/D input
ADCON1.7 = 0 ' RA.1 = +Vref, Set PORTA analog and left justify result
ADCON1.5=1 ' Set Vref- to pin 5
ADCON1.4=1 ' Set Vref+ to pin 4
PORTb.6 =0 ' Prepare RB0 for high-going pulseout

ANSEL = %00001101 ' Set PORTA.2 analog, rest digital
'ANSELH = %00000000

' Variables
outpuls VAR byte ' Variable for the calculated puls out in mS
POT_POS VAR BYTE ' Pot position CC=0, CCW=255
ampdum VAR Word ' A dummy to canculate big values
amp var word ' Calculating Ampere
LEFT CON 90 ' Left Stop position 0.70mS
RIGHT CON 163 ' Right Stop position 2.1mS

'Pause 700 ' Wait for LCD to start

MainLoop: ' The Loop start here!
ADCIN 0,POT_POS ' Read A/D channel 0 to variable SVO_POS
IF POT_POS>127 then ' Check if positive
ampdum=(7874* (POT_POS-128)) ' Then calculate the dummy
amp= div32 100 ' Let amp get the dummy value
else
ampdum=(7874 * (127-POT_POS)) ' Now it must be negative Amp so calculate
amp= div32 100 ' Let amp get the dummy value
endif ' End of test if Amp negative

'Output to LCD
Lcdout $fe, 1, "POT_POS= ", #POT_POS ' Display POT Valu between 0-255 on line 1
IF POT_POS>=127 then ' Check if + Ampere Else goto - Ampere
LCDOut $fe,$C0, "AMP= ",DEC (amp/1000),".", DEC1 amp' Display pulswith in mS on line 2
else
LCDOut $fe,$C0, "AMP= -",DEC (amp/1000),".", DEC1 amp' Display pulswith in mS on line 2
endif

'outpuls =100+(POT_POS *100/255) 'Calculate the outpuls in mS
'IF outpuls < LEFT THEN outpuls = LEFT ' Stop if puls shorter than constant LEFT
'IF outpuls > RIGHT THEN outpuls = RIGHT ' Stop if puls shorter than constant RIGHT
' Span 100 gives 100+100 = 200=2mS 150 is center
'PULSOUT portb.6 ,outpuls ' Move servo on pin
'PAUSE 20 ' Constant 20mS pulses(low) between outpuls
'GOTO MainLoop ' Forever
End

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