Thank you !
As I say, with just one resistors chain , everything works PERFECT !
My troubles appears when I try to use TWO resistors chains (and TWO ADC channel).
I wrote another version :
Code:
@ __config _XT_OSC & _WDT_OFF & _PWRTE_ON & _MCLRE_ON & _BODEN_ON & _CP_ON 

DEFINE OSC  4

DEFINE ADC_BITS     10          
DEFINE ADC_CLOCK    3
DEFINE ADC_SAMPLEUS 100      



CMCON = 7
OPTION_REG.7= 1
TRISIO      = %00000110	 		
GPIO        = %00000001
ANSEL       = %00110110
ADCON0.7    = 1

adval   var word
valb    var word
vala    var word

PAUSE 200

goto mainloop

getadv:
        PAUSEuS 50                      	' Wait for A/D channel acquisition time
        ADCON0.1 = 1
        WHILE ADCON0.1 = 1 : WEND
        adval.HighByte = ADRESH
        adval.LowByte = ADRESL
Return

getadvala:
        ADCON0 = %10000101             		
        Gosub getadv
        vala=adval
Return

getadvalb:
        ADCON0 = %10001001            		
        Gosub getadv
        valb=adval
Return

mainloop:
gosub getadvala
gosub getadvalb


if vala < 950 then
	if vala < 940 AND vala > 650 THEN gosub LED1
	IF vala < 600 AND vala > 450 THEN gosub LED2      
	IF vala < 400 AND vala > 150 THEN gosub LED3     
	IF vala < 100 THEN gosub LED4                  
endif

if valb < 950 then
	if valb < 940 AND valb > 650 THEN gosub LED1
	IF valb < 600 AND valb > 450 THEN gosub LED2
	IF valb < 400 AND valb > 150 THEN gosub LED3 
	IF valb < 100 THEN gosub LED4                   
endif

goto mainloop
But still no have proper results ...