Timer with ATtiny15/13           

by Gerd Sinning                       
Elektronik-Labor   Projekte   AVR 

This is a simple timer which I'm using to charge batteries, because I have a tendency to forget about the batteries and then they get overcharged. No good.

The time can be set with a potentiometer between 1 minute and 1023 minutes, about 17 hours. A pushbutton starts the time, turns on a relais and the timer will turn off the relais when the time is elapsed. It can be switched to seconds for a shorter time period (17 minutes) e.g. to boil eggs, also easy to forget about.

The ATTiny15 is using an internal oscillator only and needs a calibration for a 10 ms high pulse on PB1, so it is necessary to write a good calibration byte to the OSCCAL register, which is in the beginning of the program OSCCAL_val= 0x6F. It's a bit of trial and error until the 10 ms are set for your contoller but is should be done. The total time is not extremely accurate because we can't use a quartz, but for a battery charger I think it is good enough, the batteries don't mind a few minutes more or less. However, time setting with a potentiometer is quick and easy.

The circuit diagram, S1 is a switch min/sec which you may need or not, and S2 is a pushbutton to start the timer.

If 17 hours are not sufficient and a longer time is required it is possible to change the value of cnt_cmp = 100 ; 100 * 10 ms = 1 second in the program to e.g. cnt_cmp = 200, which will double the time to 34 hours. Depending on your application the time can also be much shorter, change cnt_cmp accordingly.

Any high to low transition on PB4 will start the timer, even a LDR could be connected to PB4 to make a light switch which turns on for the preset time when it is dark. It will turn off even if PB4 is still low and then waits for the switch or LDR to go high again. This also prevents a false trigger when the time is short and the button is still pressed. It is quite flexible and can be adapted to many applications which need a timer.

A possible layout of the board, top and bottom view. (the test setup before it went into the box)

The timer in a box.

It was quite easy to make and since then I'm using it whenever the batteries need charging.

download AT15timer1.asm

Tiny13-Version, Beitrag zum T13-Contest: AT13timer1.zip

This program is distributed in the hope that it will be useful but WITHOUT ANY WARRANTY;

Atmel datasheet ATtiny15, Atmel datasheet ATtiny13, Atmel.com
Gerd's AVR assembler version 2.7: http://www.avr-asm-tutorial.net/gavrasm/index_en.html
For a Scope can use: VA -- Visual Analyzer http://www.sillanumsoft.org

; AT15 timer 1-1023 minutes (17 h), 0 = 1 min
; ADC channel 1, potentiometer to set time
; switch hi=minutes, lo=seconds (17 min)
; pbStart switch Relais on , Relais off after time elapsed
; ATtiny15 GS 11-2009
; The timing is adapted for 1.6 MHz
; This program is free software; you can redistribute it and/or
; modify it under the terms of the GNU General Public License.
; This program is distributed in the hope that it will be useful,
; ATtiny15 dip
; (ADC3) PB4 PB2 (ADC1/SCK/T0/INT0)
; PB0 output toggle pin (calibrate 10 ms)
; PB1 input switch hi=minutes, lo=seconds
; PB2 input ADC channel 1 potentiometer to set time
; PB3 output active high Relais
; PB4 input start pushbutton (to lo)

.DEVICE ATtiny15 ;for gavrasm

.equ toggle = PB0
.equ swMinSec = PB1
;ADC1 = PB2
.equ Relais = PB3
.equ pbStart = PB4

.equ OSCCAL_val = 0x6F ; calibrate

.equ c_value = 250-1 ; Compare Match 10 ms, 40 x 250
.equ cnt_cmp = 100 ; 100 * 10 ms = 1 s, inc counter in TIM1_Cmp

.def S = r4
.def lowByte = r5 ; ADC
.def highByte = r6

.def temp = r16
.def counter = r17
.def flag = r20
.def cntminuteL = r21 ; main timing
.def cntminuteH = r22
.def cnt60sec = r23

.org 0
; Reset-vector to adress 0000
rjmp reset
reti ; INT0addr= 0x0001 External Interrupt 0
reti ; PCI0addr= 0x0002 Pin Interrupt Request 0
rjmp TIM1_Cmp ; OC1addr = 0x0003 Timer/Counter1 Compare Match
reti ; OVF1addr= 0x0004 Timer/Counter1 Overflow
reti ; OVF0addr= 0x0005 Timer/Counter0 Overflow
reti ; ERDYaddr= 0x0006 EEPROM Ready
reti ; ACIaddr = 0x0007 Analog Comparator
reti ; ADCCaddr= 0x0008 ADC Conversion Ready

;* "TIM1_Cmp" - Timer/counter 1 Compare Match interrupt handler
;* interrupts every 10 ms, 40 x 250
TIM1_Cmp: in S,sreg ; Updated every 10 ms, calibrate OSCCAL

sbis PINB, toggle ; skip if set
sbi PORTB, toggle ; output PORTB, toggle pin
sbic PINB, toggle ; skip if set
cbi PORTB, toggle

inc counter ; used for main timing
TIM1_ex: out sreg,S
; writing calibration byte to the OSCCAL Register.
ldi temp,OSCCAL_val ; test 10 ms
out OSCCAL,temp ; for the clock
; Port B
ldi temp,0b00010011 ; set pullup and pins
out PORTB, temp ; 1 = pull-up , 0 = float
ldi temp,0b00001001 ; 1 = output , 0 = input
out DDRB, temp ; to data direction register

; AD-Converter setup:
ldi temp, 0b00000001 ; ADC1 input=PB2, REFS0,1 =0 Vcc is RefVoltage
out ADMUX, temp ; 0..1023
ldi temp,0b11010100 ; ADC initialise single conversion and prescaler 16:
out ADCSR, temp
; timer1 setup:
; Timer/Counter1 compare match interrupt Enable
ldi temp,0b01000000 ; CTC1: Clear Timer/Counter on Compare Match
out TIFR,temp ; clear pending Interrupt
out TIMSK,temp ; set in the Timer Interrupt Mask Register
ldi temp,0 ; Timer/Counter 1 clear
out TCNT1,temp ;
ldi temp,c_value ; Timer/Counter 1 for 10 ms
out OCR1A,temp ;
ldi temp,0b10001011 ; Timer/Counter 1 clocked at CK/64 = 40 us
out TCCR1,temp ; @ 1,6 Mhz

sbi AcsR, Acd ; Disable Comparator

cbi PORTB, Relais
sei ; Enable gobal iterrupt

; timer time set with potentiometer (10k) on ADC1 1-1024 Minutes (17 h)
; read ADC1 at start

loop0: ldi flag, 1 ; remember swMinSec
sbic PINB, pbStart ; skip if button is pressed = lo
rjmp loop0 ; wait for start
clr counter
sbis PINB, swMinSec ; skip if swMinSec is hi
clr flag ; else if swMinSec is lo, seconds

debounce: cpi counter, 2
brne debounce ; debounce pbStart
sbic PINB, pbStart ; check again if button is pressed = lo
rjmp loop0

; get ADC value
sbi ADCSR, ADIF ; clear ADIF flag
sbi ADCSR, ADSC ; start conversion
wait1: ; discard first reading
rjmp wait1

sbi ADCSR, ADIF ; clear ADIF flag
sbi ADCSR, ADSC ; start conversion
wait2: ; read second ADC value
rjmp wait2
; ADC read:
in lowByte, ADCL ; low byte
in highByte, ADCH ; then high byte

tst highByte ; no zeros
brne loopset
tst lowByte
brne loopset ; ok, is <> 0
inc lowByte ; 1 is minimum

; Software-Counter-Register reset to zero
ldi counter,0 ; 10 ms
ldi cnt60sec, 0 ; 60 seconds
ldi cntminuteL,0 ; to zero L
ldi cntminuteH,0 ; to zero H

ldi temp,0 ; set register zero and ...
out TCNT1,temp ; reset hardware-counter LSB
ldi temp,0b00000010 ; set Bit 1 PSR1: Prescaler Reset Timer/Counter1
out SFIOR,temp ; Timer1 Prescaler Reset

sbi PORTB,Relais ; hi out on Relais
cpi counter, cnt_cmp ; 100 * 10 ms = 1 s, inc counter in TIM1_Cmp
brlo loop1sec

ldi counter, 0 ; back to 0 seconds

tst flag
breq loopSec ; if 0 count seconds

inc cnt60sec ; inc 60 s counter
cpi cnt60sec, 60 ; 1 s * 60 = 1 min
brlo loop1sec
ldi cnt60sec, 0 ; counter cnt60sec back to 0 minutes
inc cntminuteL ; inc main minute counter
brne niminh
inc cntminuteH

cp cntminuteH, highByte
brlo loop1sec
; now wait for High byte, Minute vs ADC
cp cntminuteL, lowByte
brlo loop1sec

cbi PORTB,Relais ; low Relais, end time loop

waithi: sbis PINB, pbStart ; skip if button is hi again
rjmp waithi ; else wait for hi
rjmp loop0 ; when time elapsed and pbStart hi

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