These are the sort of things the timer can be used for.
Just turn the dials to the required time and turn the project ON.
When the dials are turned to "0"  "0" the LED will flash but the timer will not beep.
This project replaces an electronic timer bought some 15 years ago. It used a CD4541 chip with 24 timing resistors on two 12 position rotary switches and numerous other components to produce the beep. 
But the electros went leaky and 20 minutes extended to 35 and 1 hour on the timer never produced a beep.
So this timer was born.

The timer built on surface-mount prototype PC board

CONSTRUCTION
You can build the circuit on any type of Proto board. We have chosen our surface-mount board as it makes a neat project and you can see all the wiring at the same time.
Use 4 button cells in a holder as the circuit requires very little current and they will last a long time.

The PROGRAM
This project is part of a course in PIC Programming. See left index on Talking Electronics website: List of PIC Projects: for the projects in this course.
The course consists of building these projects and modifying the programs to learn the art of programming PIC microcontrollers.
Most of the projects are very simple however they cover many different routines and enable you to build up your knowledge.
This project has been produced on our standard template and contains a number of sub-routines taken from other projects.
The hardest part of any program is interfacing it with the outside world. One of these problems is to get accurate positioning of the pots. To do this we produced a sub-routine that created a value from a loop counter. We then adjusted the interval between each "look to see when the 100n was charged" and when the loop counter was 10 for the 10 o'clock position, it was complete.
The 1 minute delay could be determined mathematically by counting the microseconds in the program but it was much easier to use a stop watch.
Finally, the LED was turned on for only 5mS per 800mS in the 1 minute delay. This is less than 1% but the flash appears to be a lot longer due to the Persistence of Vision of the eye. 
The program contains a number a new subroutine that you will be able to "cut and paste" for projects in the future.

If you want to modify the program you will need a programmer, a board to hold the 8 pin chip during programming and an adapter to connect between the programmer and PC board.
These are covered in our article "Pick-A-PIC."

Here are the files you will need for "burning" your chip and/or modifying the program:
Timer.asm
Timer.txt
Timer.hex

The following program is for viewing. It may contain spaces or hidden characters that will not compile correctly to produce a .hex file. Use the .hex file above to burn your chip or the .asm file to modify the program.

;******************************* ;Handy Timer.asm ;13-10-2010 ;******************************* list p=12F629 radix dec include "p12f629.inc" errorlevel -302 ; Don't complain about BANK 1 Registers __CONFIG _MCLRE_OFF & _CP_OFF & _WDT_OFF & _INTRC_OSC_NOCLKOUT ;Internal osc. ;_MCLRE_OFF - master clear must be off for gp3 to be input pin ;**************************************************************** ; variables - names and files ;**************************************************************** temp1 equ 20h ; temp2 equ 21h ; temp3 equ 22h ; temp4 equ 23h ; _beepA equ 24h ;for beep tone _beepB equ 25h ;for beep tone _flash equ 26h ;for flashing the LED _potA equ 27h ;holds value 1-10 for x10minutes _potB equ 28h ;holds value 1-10 for minutes _loops equ 29h ; temp equ 2Ah ; del_x equ 2Bh ; del_y equ 2Ch ; xmin_1 equ 2Dh ; xmin_2 equ 2Eh ; xmin_3 equ 2Fh ; temp_10 equ 30h ;**************************************************************** ;Equates ;**************************************************************** status equ 0x03 rp1 equ 0x06 rp0 equ 0x05 GPIO equ 0x05 status equ 03h option_reg equ 81h ; bits on GPIO pin7 equ 0 ;GP0 out for x10mins pin6 equ 1 ;GP1 in for x10mins pin5 equ 2 ;GP2 out for mins pin4 equ 3 ;GP3 in for mins pin3 equ 4 ;GP4 piezo pin2 equ 5 ;GP5 LED ;bits rp0 equ 5 ;bit 5 of the status register ;**************************************************************** ;Beginning of program ;**************************************************************** org 0x00 nop nop nop nop nop SetUp bsf status, rp0 ;Bank 1 movlw b'11001010' ;Set TRIS GP0,2,4,5 out GP1,3,input movwf TRISIO ; bcf status, rp0 ;bank 0 movlw 07h ;turn off Comparator ports movwf CMCON ;must be placed in bank 0 call flash clrf GPIO ;Clear GPIO of junk goto Main ;**************************************************************** ;* Sub Routines and delays * ;**************************************************************** ;approx 150uS delay for loops for potA and PotB _150uS movlw .67 movwf temp1 _150u nop decfsz temp1,f goto _150u retlw 00 _20mS movlw .20 movwf temp2 _20 nop decfsz temp1,f goto _20 decfsz temp2,f goto _20 retlw 00 _500mS movlw 0FFh movwf temp2 _500 goto $+1 goto $+1 decfsz temp1,f goto _500 decfsz temp2,f goto _500 retlw 00 _x1beep movlw 80h movwf del_y movlw .45 movwf del_x nop decfsz del_x,1 goto $-2 movlw b'00010000' xorwf gpio,1 ;toggle GP4 decfsz del_y,1 goto $-8 call _500mS call _500mS retlw 00 beep movlw 0ffh movwf del_y movlw .45 movwf del_x nop decfsz del_x,1 goto $-2 movlw b'00010000' xorwf gpio,1 ;toggle GP4 decfsz del_y,1 goto $-8 call _500mS call _500mS retlw 00 longbeep movlw 0ffh movwf del_y movlw 0ffh movwf del_x nop decfsz del_x,1 goto $-2 movlw b'00010000' xorwf gpio,1 ;toggle GP4 decfsz del_y,1 goto $-8 call _500mS retlw 00 ;flash LED at start-up flash movlw 0ffh movwf _flash bsf gpio,5 nop decfsz _flash,1 goto $-2 bcf gpio,5 retlw 00 ;potA = x10minutes ;Detects position of potA ; _potA will have 0-9 potA clrf _potA clrf temp bcf gpio,0 ;to discharge 100n call _20mS call _20mS bsf gpio,0 ;to charge 100n call _150uS btfsc gpio,1 retlw 00 ;_potA & temp exits with 0-9 incf _potA,1 incf temp,1 goto $-5 potB clrf _potB clrf temp bcf gpio,2 ;to discharge 100n call _20mS call _20mS bsf gpio,2 ;to charge 100n call _150uS btfsc gpio,3 retlw 00 ;_potB & temp exits with 0-9 incf _potB,3 incf temp,1 goto $-5 ;x1min - 1 minute delay x1min movlw .78 movwf xmin_3 _1min goto $+1 goto $+1 goto $+1 goto $+1 decfsz xmin_1,f goto _1min decfsz xmin_2,f goto $+2 goto $+3 bcf gpio,5 ;give the LED illumination-time goto _1min decfsz xmin_3,f goto $+2 retlw 00 bsf gpio,5 ;flash LED goto $+1 goto $+1 goto $+1 goto $+1 goto _1min x10mins movlw .10 movwf temp_10 call x1min decfsz temp_10,1 goto $-2 retlw 00 ;**************************************************************** ;* Main * ;**************************************************************** Main call potA ;returns with value in _potA and temp movlw 00h xorwf temp,0 btfsc status,2 ;temp=00=zero "x10minutes" goto min_only call longbeep ;long beep to indicate x10minutes decfsz temp,1 goto $-2 ;temp destroyed ;only _potA 1-9 will be used call x10mins decfsz _potA,1 goto $-2 ;check for x1min set on potB call potB movlw 00h xorwf temp,0 btfsc status,2 ;temp=00=zero minutes goto $+4 ; no setting on pot call x1min decfsz _potB,1 goto $-2 call beep goto $-1 min_only call potB movlw 00h xorwf temp,0 btfsc status,2 ;temp=00=zero "x10minutes" goto Main ; no sound as no setting on pots call _x1beep ;x1_beep to indicate x1minutes decfsz temp,1 goto $-2 ;temp destroyed ;only _potB 1-9 will be used call x1min decfsz _potB,1 goto $-2 call beep goto $-1 END

GOING FURTHER
You can add additional features to this project by writing your own program or modifying the program above. Send any additions to Talking Electronics for inclusion in this article.