A device for the kitchen of five independent timers. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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A device for the kitchen of five independent timers. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Clocks, timers, relays, load switches

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The proposed device will be useful in any kitchen. The timer will allow you not to monitor the cooking time, but will signal the moment of its readiness. The device contains 5 independent timers that can be set and changed at any time.

(click to enlarge)

Each timer can be set from 1 to 99 minutes. The seven-segment LED indicator HL1 displays the remaining time until the sound signal is triggered. LEDs HL2-HL6 serve to indicate the current timer, the value of which is displayed on the indicator. A buzzer is used as a sound annunciator. The timer has a memory function of the last 5 used unique (non-repeating) values. This will allow a much faster set of frequently used tenses.

In the main mode, the "+" and "-" buttons are used to select the current timer. By pressing the "Setting" button, we enter the setting mode of the selected timer. It is characterized by the flashing of the corresponding LED at a frequency of about 1 Hz. In this mode, using the "+" and "-" buttons, the set time is set. Each press changes the set time by 1 minute. By simultaneously pressing the "+" or "-" buttons and the "Memory/X10" button, the set value is changed for 10 minutes. The "Memory/X10" button also serves to quickly retrieve stored values from the EEPROM memory of the microcontroller. It consists of 5 cells and is organized like a stack, where the last stored value is retrieved first. It should be noted that the first press of this button always gives 0. This is done to be able to quickly reset the timer. Writing to memory occurs automatically when you exit the setup mode. If the time to be set is already in memory, no recording will be made. The setting mode is exited by pressing the "Setting" button again and at the same time the countdown of the set value will start. If we change our mind about starting the timer, then when exiting the setup mode, we need to set the value to 0.

A device for the kitchen of five independent timers. Photo of a kitchen timer

Each timer operates independently and can be changed at any time. After the set time has elapsed, an audible alarm will sound in the form of a sequence of intermittent sounds. Also at this moment, the LED corresponding to the timer number will flash. The alarm will continue until one of the "Memory/X10", "+" or "-" buttons is pressed.

The kitchen timer project used seven-segment indicators with a common anode. The author used a twin type A-522G. Transistors VT1-VT3 low-power silicon with npn structure, such as KT3102. Buzzer type XC1203XF 3V or equivalent.

A device for the kitchen of five independent timers. Photo of the board with the controller

Since the microcontroller program uses the values from the EEPROM, then for their safety, when installing the fuses, turn on the BOD detector at 4.3 V. The clock frequency of the internal RC oscillator is 8 MHz.

Cooking in the kitchen does not require high precision, so the microcontroller pins for connecting quartz were sacrificed in favor of functionality. The low accuracy and stability of the generated time intervals is due to the use of an internal RC generator. The error can be approximately 1-2 minutes per 1 hour with the nominal value of the counting register of timer 1, which is equal to TCNT1L=0xEE, TCNT1H=0x85. However, the accuracy can be improved. This requires changing these values. Loading the values of the counting register is carried out in the interrupt handler from timer 1, in which the time is counted. The amount of change is calculated based on the actual deviation. For example, if the time is 1 minute 40 seconds behind at a temperature of about 20 degrees and the microcontroller supply voltage is 5 volts, then the value of the timer counter register will be TCNT1L=0x83, TCNT1H=0x82.

Download source, firmware and project in P-Cad

Author: Anton Garkusha, gam-rainers [dog] mail.ru; Publication: cxem.net

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