Clock on an AVR microcontroller with DS1307. Do-it-yourself watch with LED indication Electronic circuit of a watch on a microcircuit

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15 hours of reward So, to be a creative person, it is not enough to have only a socially useful, significant worthy goal. After all, the set goal must be realized, and desire alone is not enough for this. To cross the ocean, you need to know how to build ships. To

This clock is assembled on a well-known chipset - K176IE18 (binary counter for a clock with a bell signal generator),

K176IE13 (counter for clocks with alarm clock) and K176ID2 (binary to seven-segment code converter)

When the power is turned on, zeros are automatically written to the hour and minute counter and the alarm clock memory register of the U2 chip. For installation

time, press the S4 (Time Set) button and holding it press the S3 (Hour) button - to set the hour or S2 (Min) - to set

minutes. In this case, the readings of the corresponding indicators will begin to change with a frequency of 2 Hz from 00 to 59 and then again 00. At the moment of transition

from 59 to 00 the hour counter will increase by one. Setting the alarm time is the same, you just need to hold it

button S5 (Alarm Set). After setting the alarm time, you need to press the S1 button to turn on the alarm (contacts

closed). Button S6 (Reset) is used to force the minute indicators to be reset to 00 during setup. LEDs D3 and D4 play a role

dividing dots flashing at a frequency of 1 Hz. The digital indicators on the diagram are located in the correct order, i.e. come first

hour indicators, two dividing dots (LEDs D3 and D4) and minute indicators.

The clock used resistors R6-R12 and R14-R16 with a wattage of 0.25W, the rest - 0.125W. Quartz resonator XTAL1 at a frequency of 32 768Hz -

ordinary sentry, KT315A transistors can be replaced with any low-power silicon of the appropriate structure, KT815A - with transistors

average power with a static base current transfer coefficient of at least 40, diodes - any low-power silicon. Tweeter BZ1

dynamic, without built-in generator, winding resistance 45 Ohm. Button S1 is naturally locked.

The indicators used are TOS-5163AG green, you can use any other indicators with a common cathode without reducing

resistance of resistors R6-R12. In the figure you can see the pinout of this indicator; the conclusions are shown conditionally, because presented

view from above.

After assembling the watch, you may need to adjust the frequency of the crystal oscillator. This can most accurately be done by digitally controlling

using a frequency meter, the oscillation period is 1 s at pin 4 of the U1 microcircuit. Tuning the generator as the clock progresses will require significantly more expense

time. You may also have to adjust the brightness of LEDs D3 and D4 by selecting the resistance of resistor R5, so that everything

glowed uniformly brightly. The current consumed by the clock does not exceed 180 mA.

The watch is powered by a conventional power supply, assembled on a positive microcircuit stabilizer 7809 with an output voltage of +9V and a current of 1.5A.

I present to your attention electronic microcontroller clock. The clock circuit is very simple, contains a minimum of parts, and can be repeated by beginning radio amateurs.

The design is assembled on a microcontroller and a DS1307 real-time clock. A four-digit, seven-segment LED indicator is used as an indicator of the current time (ultra-bright, blue-colored, which looks good in the dark, and, at the same time, the clock plays the role of a night light). The clock is controlled by two buttons. Thanks to the use of the DS1307 real-time clock chip, the program algorithm turned out to be quite simple. The microcontroller communicates with the real-time clock via the I2C bus, and is organized by software.

Clock diagram:

Unfortunately, there is an error in the diagram:
— the MK terminals need to be connected to the transistor bases:
РВ0 to Т4, РВ1 to Т3, РВ2 to Т2, РВ3 to Т1
or change the connection of the transistor collectors to the indicator digits:
T1 to DP1…..T4 to DP4

Parts used in the clock circuit:

♦ ATTiny26 microcontroller:

♦ real time clock DS1307:

♦ 4-digit seven-segment LED indicator – FYQ-5641UB-21 with a common cathode (ultra-bright, blue):

♦ quartz 32.768 kHz, with an input capacitance of 12.5 pF (can be taken from the computer motherboard), the accuracy of the clock depends on this quartz:

♦ all transistors are NPN structures, you can use any (KT3102, KT315 and their foreign analogues), I used BC547S
♦ microcircuit voltage stabilizer type 7805
♦ all resistors with a power of 0.125 watts
♦ polar capacitors for an operating voltage not lower than the supply voltage
♦ backup power supply DS1307 – 3 volt lithium cell CR2032

To power the watch, you can use any unnecessary cell phone charger (in this case, if the voltage at the output of the charger is within 5 volts ± 0.5 volts, part of the circuit - a voltage stabilizer on a 7805 type chip - can be eliminated)
The current consumption of the device is 30 mA.
You don’t have to install the backup battery for the DS1307 clock, but then, if the mains power goes out, the current time will have to be set again.
The printed circuit board of the device is not given; the design was assembled in a case from a faulty mechanical watch. The LED (with a blinking frequency of 1 Hz, from the SQW DS1307 pin) serves to separate the hours and minutes on the indicator.

The microcontroller settings are factory: clock frequency - 1 MHz, FUSE bits do not need to be touched.

Clock operation algorithm(in Algorithm Builder):

1. Setting the stack pointer
2. Setting timer T0:
— frequency SK/8
- overflow interrupts (at this preset frequency, the interrupt is called every 2 milliseconds)
3. Initialization of ports (pins PA0-6 and PB0-3 are configured as output, PA7 and PB6 as input)
4. Initialization of the I2C bus (pins PB4 and PB5)
5. Checking the 7th bit (CH) of the DS1307 register zero
6. Global interrupt enable
7. Entering a loop and checking if a button is pressed

When turned on for the first time, or turned on again if there is no backup power to the DS307, the current time is reset to the original setting. In this case: button S1 – to set the time, button S2 – transition to the next digit. Set time - hours and minutes are written to the DS1307 (seconds are set to zero), and the SQW/OUT pin (7th pin) is configured to generate square wave pulses with a frequency of 1 Hz.
When you press the S2 button (S4 - in the program), a global interruption is disabled, the program goes into the time correction subroutine. In this case, using the S1 and S2 buttons, tens and units of minutes are set, then, from 0 seconds, pressing the S2 button records the updated time in the DS1307, resolves the global interrupt and returns to the main program.

The watch showed good accuracy, the time loss per month was 3 seconds.
To improve accuracy, it is recommended to connect quartz to the DS1307, as indicated in the datasheet:

The program is written in the Algorithm Builder environment.
Using the clock program as an example, you can familiarize yourself with the algorithm for communicating between the microcontroller and other devices via the I2C bus (each line is commented in detail in the algorithm).

Photo of the assembled device and printed circuit board in .lay format from site reader Anatoly Pilguk, for which many thanks to him!

The device uses: Transistors - SMD BC847 and CHIP resistors

Attachments to the article:

(42.9 KiB, 3,304 hits)

(6.3 KiB, 4,247 hits)

(3.1 KiB, 2,707 hits)

(312.1 KiB, 6,002 hits)

(11.4 KiB, 1,999 hits)

The choice of the series of microcircuits on which this circuit will be implemented is extremely important. For a clock, the most important parameter is the current consumed by it, since in most cases either the entire clock or part of the clock circuit is powered by batteries. Therefore, when developing a circuit, we will choose microcircuits implemented in .

Let's start developing the clock circuit with a quartz oscillator. As already discussed when developing the block diagram, a clock quartz resonator will be used as part of the generator. To reduce the cost of the entire device as a whole, we will use the simplest generator circuit - a capacitive three-point, and since the generator is designed to synchronize a digital device, the generator will be implemented on a logical inverter. The schematic diagram of such a quartz oscillator is shown in Figure 1.

Let me remind you that resistor R1 is designed to automatically start the generator when the power is turned on. The same element determines the gain of the inverter, and the greater this gain is, the more rectangular oscillations will be formed at its output, and this, in turn, will lead to a decrease in the current consumed by the quartz oscillator. Let's choose R1 equal to 10 Mohm.

R2 is designed to prevent self-excitation of the generator at a frequency determined by the capacitance of the crystal holder. Let's choose the resistance value of this resistor 510 kOhm.

The second one in the generator circuit is designed to reduce the duration of the fronts of the generated rectangular oscillation. This is necessary to reduce the influence of the subsequent circuit on the stability of the master oscillator oscillations, as well as for more reliable operation of the frequency divider digital counters.

As a microcircuit containing inverters, we will choose the SN74LVC2G04DRL microcircuit. This chip, built using CMOS technology, contains two inverters. The fact that the microcircuit contains two elements is indicated by the designation 2G. The fact that these are inverters is indicated by the number 04, and the fact that the microcircuit uses a package with a lead pitch of 0.5 mm is indicated by the letters DRL. The dimensions of the case of this microcircuit do not exceed 1.6 * 1.6 mm (the case has only six pins). The microcircuit is capable of operating in a voltage range from 1.5 to 5.5 V.

Next we implement a frequency divider circuit up to a value of 1 Hz. Let me remind you that the period of oscillations with a frequency of 1 Hz is equal to 1 second. As we already determined when developing the block diagram, its division coefficient should be equal to 32768. That is, to implement the divider, 15 counting triggers will be required. Of course, you can take the K176IE12 chip, specially designed for this purpose, but we are not looking for easy ways, so we use the universal SN74HC393PW chip. It has two independent four-bit binary counters. This means that only two microcircuits will be enough to implement our divider.

The case dimensions of the selected microcircuit do not exceed 5´6.4mm. The body of this microcircuit has 14 pins. If there are no special requirements for the dimensions of the watch, then you can use the domestic K1564IE19 microcircuit. Its case is more than twice larger than the case of the selected microcircuit. However, even the pin numbers of the microcircuits will be the same. The resulting circuit diagram of the second pulse generator of an electronic clock is shown in Figure 2.

Now remember that the time interval generator requires another frequency divider. The pulse period at its output will be equal to 1 minute. The divider by sixty can be implemented on exactly the same chip that we used earlier to build a divider by 32768.

The divisor by sixty is not a multiple of a power of two, so implementing it will require feedback. To simplify the diagram, note that the number 60 is divided into the numbers 10 and 6. Both numbers contain only two ones. The pins of the 4-bit counters go to different sides of the microcircuit body. Therefore, it will be convenient to use two independent logical elements “2I”. This will significantly simplify the layout of the printed circuit board and reduce the length of the connecting wires, thereby reducing the area of ​​the printed circuit board and possible interference from the operating circuit.

We use two SN74LVC1G08DRLR microcircuits as “2I” logic elements. We determine that the microcircuit contains only one logical element by the symbols 1G, and that it is a logical element “2I” by the numbers 08. The dimensions of the case of the selected microcircuit do not exceed 1.6 × 1.6 mm. Domestic versions of such a microcircuit, for example K1554LI1, contain four logic elements in one package, the distance between the pins is at least 1.25 mm. As a result, a circuit assembled on such microcircuits will be identical in electrical parameters, but will be smaller in size.

The resulting frequency divider circuit by 60, generating pulses with a period of 1 minute and consisting of serially connected dividers by 10 and by 6, is shown in Figure 3. The circuit is implemented on only three microcircuits. Using feedback from pins Q1 and Q3 turns binary counter D1.1 into decimal, and using feedback from pins Q1 and Q2 of chip D1.2 implements a modulo 6 counter.

So, we have completed the development of a minute pulse generator. In total, we needed six chips, three of which are small logic chips and take up minimal space on the printed circuit board of a digital device.

Now we can begin to develop the circuit diagram of the time interval counter. As we already found out when developing the block diagram of the clock, this counter includes exactly the same divider by 60 as in the minute pulse generator, so you can use the same circuit. The only difference is that this time we will need all the counter outputs. We will suppress the signals from these pins to the input of the display unit.

The last counter that we need to implement the time interval counter block is a counter for 24. It would be convenient to implement this counter on a decimal counter chip, but dual asynchronous decimal counter chips are not produced, so we implement the clock counter on the same chip as the others clock blocks - SN74HC393PW.

The difficulty in implementing this scheme is that the counting coefficient is not a multiple of ten, so the feedback signal must be applied to both counters simultaneously. It would be possible to implement this counter in binary form, but then there would be difficulties with displaying the contents of this counter. In order to implement a decimal counter on the first 4-bit counter and at the same time be able to reset the entire hour counter at the beginning of the day, we use an additional logical element “2OR”. A reset signal at the output of this microcircuit will appear either when the first counter reaches the number 10, or when the entire counter reaches the value 24.

As a logical element “2OR” we use a small logic microcircuit, similar to the already used “2I” microcircuit. This is the SN74LVC1G32DRLR chip. The number 32 in the name of the microcircuit designates the logical element “2OR”. The case dimensions of this microcircuit do not exceed 1.6´1.6mm. As a result, despite the slightly more complex circuit diagram, the area occupied by the hour counter is significantly reduced.

The complete circuit diagram of a clock pulse counter implemented on the SN74HC393PW chip is shown in Figure 4. Using feedback from pins Q1 and Q3 of the first chip turns it into a decimal counter. To implement a modulo 24 counter, we use feedback from output Q1 of the high-order digit of the counter (two) and output Q2 of the low-order digit of the clock counter (four).

Thus, we have implemented the main part of the clock circuit, but as already discussed when developing the block diagram, this is not enough. It is required to be able to display the received digital information. Let's move on to developing the clock display unit.

Literature:

Along with the article “Development of a clock circuit diagram” read: