Post by thread:Q: Code for simple A/D one pin 16F84?

Looking for code that will give me a simple A/D conversion for use on a PWM lamp brightness control. No linearity required. Seven or eight bits. Hardware would be a 10k variable resistor to a 0.1uF cap to ground. I've had a look at the Scott Edwards book, the section on "pot", but I don't understand the mnemonics there. I'm sure I could write it myself, but that's another couple of hours at my experience level. ;-} -- James Cameron (spam_OUTjames.cameronTakeThisOuTdigital.com) Digital Equipment Corporation (Australia) Pty. Ltd. A.C.N. 000 446 800

Hi, if you want to measure a resistor, use the AN 512. A lot of topics is written before. I tried it and works fine. (It needs three pins, however, and one of them MUST be the RA4, due to its Schmitt-trigger input.) Good luck: Imre On Fri, 24 Jul 1998, James Cameron wrote: {Quote hidden}> Looking for code that will give me a simple A/D conversion for use on > a PWM lamp brightness control. No linearity required. Seven or eight > bits. > > Hardware would be a 10k variable resistor to a 0.1uF cap to ground. > > I've had a look at the Scott Edwards book, the section on "pot", but I > don't understand the mnemonics there. > > I'm sure I could write it myself, but that's another couple of hours at > my experience level. ;-} > > -- > James Cameron (.....james.cameronKILLspam@spam@digital.com) > Digital Equipment Corporation (Australia) Pty. Ltd. A.C.N. 000 446 800 > >

Hello James. > I've had a look at the Scott Edwards book, the section on "pot", but I > don't understand the mnemonics there. Oh dear, let me try... Untested code, review before use! ; POT ; This program shows a technique for reading resistance. The pot input ; pin can only be changed during assembly, not once the program is ; running. cblock 8 temp:1 ; Temporary counter for delay. potL:1 ; Low byte of Pot measurement. potH:1 ; High byte of Pot measurement. ; forgot mnemonic for end of cblock... #define pot ra,0 ; Pin assigned to pot. #define out_pot 0 ; Value to set ra.0 to output for pot. #define in_pot 1 ; Value to set ra.0 to input for pot. ; not sure on these: device pic16c55,xt_osc,wdt_off,protect_off reset start mov macro dest,val movlw val movwf dest,f endm djnz macro reg,dest decfsz reg,f goto dest endm org 0 start bsf status,rp0 mov ra,out_pot ; RA.0 to output. mov rb,0 ; All outputs for LEDs. bcf status,rp0 bsf pot ; Start charging cap. mov potL,8 ; Set up for 6-ms delay: 8 trips wait djnz temp,wait ; through outside loop x 256 djnz potL,wait ; x 3 cycles for inside loop = 6.1 ms. clrf potL clrf potH bsf status,rp0 mov ra,in_pot ; Get input from pot. bcf status,rp0 bcf pot ; Clear output latch for pot bit. loop btfss pot ; IF pot = 0 goto done ; THEN done bsf status,rp0 mov ra,out_pot ; Discharge cap a little. mov ra,in_pot ; Change pot pin to input. bcf status,rp0 incfsz potL ; Incerement potL. goto loop ; If zero then potL overfolowed, so incfsz potH ; increment potH. If it overflows, exit. goto loop ; Overflow? No: loop. done mov temp,2 ; Divide 16-bit number represented by div bcf status,carry ; potH and potL by 2^temp (in this case, rrf potH,f ; 2^2 or 4). This scales the pot value rrf potL,f ; to fit within an 8-bit range. djnz temp,div mov rb,potL ; Show the outcome on LEDs. goto start ; Do it again. -- Cheers, Paul B.