The proposed device will be useful in any kitchen. The timer will allow you to monitor the cooking, and will signal her readiness. The device contains 5 independent timers that can be set and changed at arbitrary times.
Each timer can be set from 1 to 99 minutes. Led seven-segment indicator HL1 shows the time remaining until the alarm beeps. LEDs HL2-HL6 serve to indicate the current timer value which is displayed on the indicator. As the sound of the siren buzzer used. The timer has a memory function 5 last used unique values. This will allow much faster to produce a set of commonly used times.
In native mode buttons "+" and "-" are used to select the current timer. Clicking the button "Setting" we enter into the setting mode of the selected timer. It is characterized by flashing of the corresponding led light with a frequency of about 1 Hz. In this mode, using the buttons "+" and "-" is set set time. Each press changes the set time for 1 minute. While pressing "+" or "-" button and "Memory/X10" change set value occurs at 10 minutes. The Memory/X10" also is used to quickly retrieve stored values from EEPROM memory of the microcontroller. It consists of 5 cells, and is organized on the principle of the stack, where the first retrieves the last saved value. It should be noted that the first press of this button gives always 0. This is done to be able to quickly reset the timer. Writing to memory is done automatically when you exit the setting mode. If the set time is already in memory, then the write is not performed. Exit setup mode by pressing again on the button "Install" and simultaneously starts the countdown of the set value. If we decided not to start the timer, then when you exit the setting mode must be set to 0.
Each timer operates independently, and at any time you can edit its value. After the set time work audible alarm as a series of intermittent sounds. Also at this point will blink corresponding to the number of the timer led. The alarm will work until then, until you press one of the buttons "Memory/X10", "+" or "-".
In the draft of the kitchen timer is used seven-segment display with common anode. The author used a twin-type A-522G. Transistors VT1-VT3 low-power silicon n-p-n structure, for example KT3102. Buzzer type XC1203XF on voltage of 3 V or similar.
Since the microcontroller program uses the values from EEPROM, for their preservation should, when setting the fuse bits to enable BOD detector at 4.3 V. the Clock frequency of the internal RC oscillator is 8 MHz.
For cooking in the kitchen does not require high precision, so the pins of the microcontroller to connect the quartz were donated in favor of functionality. Low accuracy and stability of the generated time intervals due to the use of the internal RC oscillator. The error may be about 1-2 minutes to 1 hour at the rated value of the counting register timer 1, which is TCNT1L=0xEE, TCNT1H=0x85. However, the accuracy can be improved. For this you need to change these values. The loading values of the counting register are implemented in the handler for the timer interrupt 1, and in which time is counted. The magnitude of change is calculated based on the actual deviation. For example, if the time is behind by 1 minute 40 seconds at a temperature of about 20 degrees and the supply voltage of the microcontroller is 5 volts, then the value of the counting register of the timer is equal TCNT1L=0x83, TCNT1H=0x82.
Download the source code, firmware and project in P-Cad
Author: Anton Garkusha, gam-raingers [dog] mail.ru; Publication: www.cxem.net