Clock-alarm clock with a thermometer on the microcontroller. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Clock-alarm clock with a thermometer on the microcontroller. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Microcontrollers

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The functions of the actual clock in the presented device are performed by the DS1307 chip. Such microcircuits in foreign literature are usually called RTC - Real Time Clock (real time clock). RTC backup power from a lithium cell allows you not to interrupt the time count when the main power supply is turned off. There is no need to reset the time each time. The current drawn by the DS1307 is comparable to the cell's self-discharge current, so it won't need to be replaced for several years. The set alarm time is stored in the non-volatile memory of the microcontroller. Once a minute, the indicator displays the temperature value in the room for three seconds. An audible signal sounds at the beginning of every hour.

The clock scheme is shown in fig. 1.

Fig. 1

Microcontroller DD3 (PIC16F84A) initializes RTC DD2, reads and, if necessary, corrects the current time. It performs similar operations with the temperature sensor VK1 (DS1621). Both microcircuits are connected to the microcontroller via the I bus.²C. In addition, it controls the dynamic display and polls the keyboard. When the power is turned on, the microcontroller, in addition to other necessary operations, transfers the value of the alarm time stored there to the RAM from the non-volatile memory. Dynamic indication is organized as follows. The microcontroller loads the serial code into the shift register DD1 information for output to the indicator HG1, then turns on this indicator for a certain time, opening the transistor VT1. The same operations are alternately performed with indicators HG2 - HG4. In the display cycle, the state of the buttons SB1 - SB6 is also polled. Having detected a low level at its input PA0, which signals a pressed button, the microcalculator executes the pressing processing subroutine.

The purpose of the buttons is as follows:

SB1 - turns on and off the sound signal given at the beginning of each hour. When the signal is turned off, the dot on the HG4.SB2 indicator is on - after the first press of the button, the HG3 and HG4 indicators (digits of minutes) start flashing. In this state, using the buttons SB4 and SB6, you can increase or decrease the value in these bits. The same operations with clock bits (indicators HG1 and HG2) are performed after the second press of the SB2 button. By the third click on it, the updated value of the current time is written to the RTC and the clock is returned to the operating mode.

SB3 - turns on and off the alarm signal and the HL1 LED, which starts blinking in time with the HL2 LED. Within three seconds after pressing the SB3 button, the set alarm time is displayed on the indicators.

SB4 - increases the value displayed on the indicator. SB5 - after the first press of this button, the indicators display the set alarm time. After further pressing, the set time can be changed in the same way as setting the current time. After the fourth pressing, information about the operation time is entered into the non-volatile memory of the microcontroller and the clock returns to the operating mode.

SB6 - reduces the value displayed on the indicator.

The watch is assembled in a case from the watch "QUARTZ-025". A transformer was also used from them, the voltage on its secondary winding was reduced to 8 V by unwinding the turns. The details of the new watch are mounted on a printed circuit board made of foil fiberglass, the drawing of which is shown in fig. 2.

Alarm clock with a thermometer on a microcontroller

The jumper shown by a dashed line is made of an insulated wire (for example, MGTF-0,12) and installed on the side of the printed conductors. The remaining jumpers (non-insulated) are installed on the side of the parts. The board is designed to install fixed resistors MLT or C2-33, oxide capacitors K50-35 or imported ones. Capacitors C3, C5, C6 - ceramic or film.

L-34GD LEDs can be replaced with others with a housing diameter of 3 mm, and FYS-10012BUG indicators can be replaced with any suitable size with common element anodes. Color of a luminescence of light-emitting diodes and indicators - green. For indicators, panels are provided made from panels for microcircuits. Sound signaling device HA1 is installed on the side of printed conductors. Throttle L1 - DPM-0,2. The DS1621 temperature sensor is installed in a panel outside the watch case and connected to the printed circuit board with a four-wire harness. G1 lithium cell holder removed from an old computer motherboard.

Download program and firmware for MK

Author: V. Kiba, Kamensk-Shakhtinsky, Rostov Region; Publication: cxem.net

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