I recently bought network LEDs watch VST-731. The watch is distinguished from other models by its functionality, the large size of the indicator symbols and the bright glow of these symbols. Unfortunately, the software reduction of brightness at night (10 p.m. – 7 a.m.) advertised on the online store’s website was not available in this watch model. Due to the lack program control brightness of the indicators, one of the advantages of the watch - the bright glow of the symbols - is also its disadvantage: the clock numbers glow too brightly in the dark, creating some discomfort at night.

The proposed scheme for automatically adjusting the brightness of clock indicators allows you to automatically set the brightness of the indicator depending on the level of illumination of the place where the clock is located.

To build an automatic brightness control circuit, let's look at the power circuits of the VST-731 clock components. Below is a fragment electrical diagram, similar to the circuit diagram of this watch - I could not find the VST-731 circuit diagram.

The diagram shows that the power supply for different groups of display indicator segments is organized from two half-wave rectifiers assembled on diodes D1, D2. Resistors R2, R4 set the current through the indicator segments, and therefore the brightness of the symbols.

The principle of operation of automatic adjustment of the brightness of the indicator for the VST-731 watch or similar power circuits is illustrated by the diagram:

Transistor T1 in this circuit performs the functions of a regulating element and a rectifying diode. Elements D1, C1 – formation circuit DC voltage. If all clock nodes are connected to the same constant voltage source, then this circuit is not necessary: ​​the circuit on resistors R1 - R3, which sets the base current of transistor T1, can be connected to +UCC. With increasing illumination, the resistance of the photoresistor R1 decreases, while the current through the transistor T1 increases, which leads to an increase in the brightness of the indicator segments turned on by the microcircuit-controlled keys. Resistor R2, the resistance of which is several orders of magnitude lower than the resistance of photoresistor R1 in the dark, determines the brightness of the LEDs in the dark. The second brightness control channel is assembled on transistor T2, similar to the first. In our case, the second channel is necessary because, as noted above, the nodes in the clock are powered from two DC voltage sources.

The diagram for automatically adjusting the brightness of indicators for the VST-731 watch (highlighted in color) looks like this:

Mounting circuit elements (except for the photoresistor) can be done on a separate board, for example, a piece of a breadboard, and place this board in the watch case - there is plenty of empty space there. Photoresistor 1R1 must be fixed on the front panel of the watch, having previously drilled two holes for its leads. I glued a photoresistor on top trademark® in the VST® inscription on the front panel, but this is a matter of taste: the main thing is that the sensor should be located in the plane of the watch display. Before connecting the brightness control board to the clock control board, do not forget to break the old power circuits of the indicator segments (diodes D1, D2), which were mentioned above.

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
1D1	Rectifier diode	1N4007	1			To notepad
1T1, ​​1T2	Bipolar transistor	2N2222A	2			To notepad
1S1	Capacitor	47 µF	1	10V		To notepad
1R1	Photoresistor	GL5528	1			To notepad
1R2	Resistor	1.5 kOhm	1			To notepad
1R3, 1R5	Resistor

Buying a table clock today is not difficult, since similar products are found in many specialized and other stores. They can not only serve their intended purpose - to inform about the current time, but also decorate the interior or workplace, in particular. There are different models of similar products, so you can always choose interesting option, which would please any person. A luminous table clock will be very convenient to use, especially when it’s late in the day and problems with lighting arise. You won't have to constantly approach the clock to find out the time. Note that the intensity and color of the backlight can be adjusted in some models of table clocks. The functionality of such devices varies, so it is extremely important to pay attention to their specifications before the purchase.

A luminous table clock will make an excellent gift for a loved one. They will be guaranteed to be used and will bring comfort to workplace. Such things are appropriate not only in the office, but also at home. Practice shows that the demand for table clocks has not decreased over the years, as it is a convenient and affordable thing. Anyone can buy a table clock in Moscow, but first it is important to decide which model is required. Some of them are equipped with timers, alarm clocks, stopwatches and other options, but for some people they may seem unnecessary, and they will not want to overpay for unnecessary functionality. You can choose a model that will perform its basic functions according to affordable price. The table clock store offers a wide range of specialized products, among which you will be able to find the right option.

Differences between table clocks

The table clock store offers a large selection of products, but they are all radically different from each other. Products can be manufactured in different countries, from different materials and components. All this affects the final cost of the product. The main thing is to take into account all your wishes at the stage of purchasing such products. The price of a table clock depends on whether it is made domestically or abroad, whether it is mechanical or electronic, as well as other factors. It is important to understand that there are also plenty of interesting models in the low price range, so you can get good product without overpaying for it. The price of a table clock is affordable for everyone, so there is no reason not to use such accessories.

This article describes a clock on an ATMega48PA microcontroller with LED indicators and many functions:

1. Automatic brightness adjustment depending on lighting conditions.
2. Control your watch using touch buttons.
3. Built-in stopwatch
4. Built-in timer
5. Built-in alarm clock
6. Day of year indicator, from 1 to 365.
7. Sending current time via UART interface every minute.
8. Time and date setting menu.
9. Switch between HH:MM and MM:SS modes.
10. Animation of the end of the day, drawing zeros during the transition 23:59-00:00.

The watch is a rectangular box and stand made of plastic (polyvinyl chloride). All parts of the body are cut out with a knife and glued together with instant glue. On the front of the case there is a dark filter that filters out some of the red light from the indicators. There are three touch buttons on the stand. Each button is a circle of small diameter, cut out of copper foil and glued to the base with glue. On the back side there are: a connector for connecting the power adapter and external devices, and a speaker sound hole. On top there is a photocell that responds to changes in lighting. The indicators on the clock are seven segment LED indicators, with connection type: common cathode. The watch has four indicators in total, meaning four numbers can be displayed simultaneously with additional dots at the bottom. The clock works from network adapter with an output voltage of 5 volts and a minimum current of at least 150 mA.

When you turn it on for the first time, you need to set the clock. To do this, you need to press and hold the middle button (hereinafter SC) for 2 seconds, the watch will go into setting mode. Then you need to set the current hour using the left and right buttons (hereinafter referred to as LC and PC, respectively) and press SC. You also need to set the minutes. Then, in the same way, you will need to set the current day and press SK (further in all additional modes the same number settings will be used). The watch will switch to the main mode HH:MM (mode 0), that is, the indicators display hours and minutes. By pressing the SC once, you can switch to the MM:SS mode (mode 1) and back. If you press the LC in mode 0, the watch will enter alarm mode. After setting the signal time, you need to press and hold PC or LAN for 2 seconds. At the appointed time, a tone with a frequency of about 700 Hz will turn on, after 10 seconds the signal will turn off and the alarm will automatically deactivate. If you press PC in mode 0, the watch will enter timer mode. By default, the timer is set to 5 minutes. After setting the time, press and hold PC or LAN for 2 seconds and the timer will be activated. After the time has elapsed, just as with the alarm clock, a tone will ring and turn off after 10 seconds. If you press PC in mode 1, the watch will switch to stopwatch mode. By pressing LC, the stopwatch starts or stops; by pressing PC, the stopwatch is reset. If you press LK in mode 1, the watch will switch to date mode, and the current day of the year will appear on the indicators. You can press any button to exit this mode. Also, from additional modes you can switch to the main mode by pressing SK. Since all additional modes are parallel, you can set an alarm, set a timer and start a stopwatch at the same time.

The brightness of the indicators changes depending on the lighting; during the day the watch shines brightly, at night it shines dimly. Just a few gradations of brightness, which are calculated based on the readings of the photosensor.

The watch has a UART interface, with which every minute external devices(if any) 2 bytes are sent: the hour byte with the eighth bit set (for example, if it is 15 hours, then the byte is 15+128=143), and the minutes byte. The eighth bit when transmitting the clock is used so that external devices can immediately determine whether the hour byte or the minute byte is being transmitted. You can connect other devices to the AVR and receive the current time via UART.

Every midnight (when moving from 23:59 to 00:00), a simple animation is played on the indicators in the form of alternate drawing of zeros, after which the clock continues to work as normal.

Fuse bits:

In the attached file: project in Proteus, firmware, source, printed circuit board in Slayout.

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
MCU1	MK AVR 8-bit	ATmega48PA-AU	1			To notepad
VT1-VT4	Bipolar transistor	KT3130A9	4			To notepad
VT5-VT12	Transistor	KT218A	8			To notepad
C1	Electrolytic capacitor	1000uF 6.3v	1			To notepad
C2, C3	Capacitor	20 pf	2			To notepad
R1	Resistor	200 Ohm	1			To notepad
R3-R5	Resistor	1 MOhm	3			To notepad
R6-R17	Resistor	390 Ohm	12			To notepad
R18	Resistor	150 Ohm	1			To notepad
R19-R25	Resistor	68 ohm	7			To notepad
R2, R26	Resistor	10 kOhm	2			To notepad
R27	Resistor	470 Ohm	1			To notepad
LDR1	Photoresistor	1-50 kOhm	1			To notepad
Z1	Quartz	8MHz	1