Recently, watches with gas-discharge indicators have become very popular. These clocks give many people the warm light of their lamps, create comfort in the home and an indescribable feeling of breathing the past. Let's figure out in this article what these watches are made of and how they work. I’ll say right away that this is a review article, so many unclear places will be discussed in more detail in the following articles.
The clock can be divided into the following functional blocks:
1)High voltage block
2)Display block
3)Time counter
4)Backlight unit
Let's look at each of them in more detail.
High voltage block
In order for the number inside the lamp to light up, we need to apply voltage to it. The peculiarity of gas-discharge lamps is that the voltage required is quite high, about 200 Volts DC voltage. The current for the lamp, on the contrary, should be very small.
Where can you get this kind of tension? The first thing that comes to mind is a power outlet. Yes, you can use rectified mains voltage. The diagram will look like this:
The disadvantages of this scheme are obvious. This is the absence of galvanic isolation; there is no safety or protection of the circuit at all. Thus, it is better to check the lamps for functionality, while being extremely careful.
In watches, the designers took a different route, increasing the safe voltage to the required level using a DC-DC converter. To put it very briefly, such a converter works on the principle of a swing. We can, by applying a slight hand force to the swing, give it a fairly large acceleration, right? The DC-DC converter is the same: we pump low voltage to high voltage.
I will give one of the most common converter circuits (click to enlarge, the circuit will open in a new window)
A circuit with a so-called semi-driver field-effect transistor. Provides enough power to power six lamps without getting as hot as an iron.
Display block
The next functional block is indication. It consists of lamps in which the cathodes are connected in pairs, and the anodes are connected to optocouplers or transistor switches. Typically, watches use dynamic display in order to save space on the printed circuit board, miniaturize the circuit, and simplify board layout.
Time counter
The next block is a time counter. The easiest way to do this is on a specialized DS1307 chip
It provides excellent time accuracy. Thanks to this chip, the watch maintains the correct time and date, despite a long power outage. The manufacturer promises up to 10 years (!) of battery life from a CR2032 round battery.
Here is a typical connection diagram for the DS1307 chip:
There are also similar microcircuits that are produced by many companies producing radio components. These chips can provide particularly accurate timekeeping, but they will be more expensive. It seems to me that their use in household watches is not advisable.
Backlight block
The backlight unit is the simplest part of the watch. It is installed at will. These are just LEDs under each lamp that provide background lighting. These can be single-color LEDs or RGB LEDs. In the latter case, you can choose any color of the backlight or even make it change smoothly. In the case of RGB, an appropriate controller is required. Most often, this is done by the same microcontroller that counts time, but to simplify programming, you can install an additional one.
Well, now a few photos of a rather complex clock project. It uses two PIC16F628 microcontrollers to control the time and lamps and one PIC12F692 controller to control the RGB backlight.
Turquoise backlight color:
And now green:
Pink color:
All these colors can be adjusted with one button. You can choose any one. RGB diodes are capable of producing any color.
And this is a piece of a high-voltage converter. Below in the photo is a field-effect transistor, an ultra-fast diode and a storage capacitor of a DC-DC converter
The same converter, bottom view. An SMD choke and an SMD version of the MC34063 chip are used. In the photo, the remaining flux has not yet been washed off.
And this is a simplified four-lamp version of the watch. Also with RGB backlighting
Well, this is a classic clock structure based on Sunny Clock gas-discharge lamps, static backlighting and a slightly unusual way to control lamps using a pair of K155ID1 decoders
In the next article we will talk in more detail about DC-DC converters and high voltage production. We will also analyze in detail the process of assembling such a converter and run a lamp from it.
Thank you everyone, El Kotto was with you. Join the group in contact
This article will focus on making original and unusual watches. Their uniqueness lies in the fact that the time is indicated using digital indicator lamps. Once upon a time, a huge number of such lamps were produced, both here and abroad. They were used in many devices, from watches to measuring equipment. But after the advent of LED indicators, the lamps gradually fell out of use. And so, thanks to the development of microprocessor technology, it became possible to create watches with a relatively simple circuit using digital indicator lamps.
I think it would not be amiss to say that mainly two types of lamps were used: fluorescent and gas-discharge. The advantages of luminescent indicators include low operating voltage and the presence of several discharges in one lamp (although such examples are also found among gas-discharge indicators, but they are much more difficult to find). But all the advantages of this type of lamp are offset by one huge disadvantage - the presence of a phosphor, which burns out over time, and the glow dims or stops. For this reason, used lamps cannot be used.
Gas discharge indicators are free from this drawback, because a gas discharge glows in them. Essentially, this type of lamp is a neon lamp with multiple cathodes. Thanks to this, the service life of gas-discharge indicators is much longer. In addition, both new and used lamps work equally well (and often used ones work better). However, there are some drawbacks - the operating voltage of gas-discharge indicators is more than 100 V. But solving the problem with voltage is much easier than with a burn-out phosphor. On the Internet, such watches are common under the name NIXIE CLOCK: 
The indicators themselves look like this:
So, everything seems clear about the design features, now let’s start designing the circuit of our watch. Let's start by designing a high-voltage voltage source. There are two ways here. The first is to use a transformer with a secondary winding of 110-120 V. But such a transformer will either be too bulky, or you will have to wind it yourself (the prospect is so-so). Yes, and voltage regulation is problematic. The second way is to assemble a step up converter. Well, there will be more advantages: firstly, it will take up little space, secondly, it has short-circuit protection and, thirdly, you can easily adjust the output voltage. In general, there is everything you need to be happy. I chose the second path, because... I had no desire to look for a transformer and winding wire, and I also wanted something miniature. It was decided to assemble the converter on MC34063, because I had experience working with her. The result is this diagram:
It was first assembled on a breadboard and showed excellent results. Everything started immediately and no configuration was required. When powered by 12V. the output turned out to be 175V. The assembled power supply of the watch looks like this:
A linear stabilizer LM7805 was immediately installed on the board to power the clock electronics and a transformer.
The next stage of development was the design of the lamp switching circuit. In principle, controlling lamps is no different from controlling seven-segment indicators, with the exception of high voltage. Those. It is enough to apply a positive voltage to the anode and connect the corresponding cathode to the negative supply. At this stage, two tasks need to be solved: matching the levels of the MK (5V) and lamps (170V), and switching the cathodes of the lamps (they are the numbers). After some time of thought and experimentation, the following circuit was created to control the anodes of the lamps:
And controlling the cathodes is very easy; for this they came up with a special K155ID1 microcircuit. True, they have long been discontinued, like lamps, but buying them is not a problem. Those. to control the cathodes, you just need to connect them to the corresponding pins of the microcircuit and submit data in binary format to the input. Yes, I almost forgot, it is powered by 5V. (well, a very convenient thing). It was decided to make the display dynamic, because otherwise, you would have to install K155ID1 on each lamp, and there will be 6 of them. The general scheme turned out like this:
Under each lamp I installed a bright red LED (it’s more beautiful this way). When assembled, the board looks like this:
We couldn’t find sockets for the lamps, so we had to improvise. As a result, the old connectors, similar to modern COM, were disassembled, the contacts were removed from them, and after some manipulations with wire cutters and a file, they were soldered into the board. I didn’t make panels for the IN-17, I did them only for the IN-8.
The hardest part is over, all that remains is to develop a circuit for the “brain” of the watch. For this I chose the Mega8 microcontroller. Well, then everything is quite easy, we just take it and connect everything to it in the way that is convenient for us. As a result, the clock circuit included 3 buttons for control, a DS1307 real-time clock chip, a DS18B20 digital thermometer, and a pair of transistors for controlling the backlight. For convenience, we connect the anode keys to one port, in this case it is port C. When assembled, it looks like this:
There is a small error on the board, but it has been corrected in the attached board files. The connector for flashing the MK is soldered with wires; after flashing the device, it should be unsoldered.
Well, now it would be nice to draw a general diagram. No sooner said than done, here it is:
And this is what it all looks like assembled:
Now all that remains is to write the firmware for the microcontroller, which is what was done. The functionality turned out to be as follows:
Display time, date and temperature. When you briefly press the MENU button, the display mode changes.
Mode 1 - time only.
Mode 2 - time 2 min. date 10 sec.
Mode 3 - time 2 min. temperature 10 sec.
Mode 4 - time 2 min. date 10 sec. temperature 10 sec.
When held, the time and date settings are activated, and you can navigate through the settings by pressing the MENU button.
The maximum number of DS18B20 sensors is 2. If the temperature is not needed, you can not install them at all; this will not affect the operation of the watch in any way. There is no provision for hot plugging of sensors.
Briefly pressing the UP button turns on the date for 2 seconds. When held, the backlight turns on/off.
By briefly pressing the DOWN button, the temperature is turned on for 2 seconds.
From 00:00 to 7:00 the brightness is reduced.
The whole thing works like this:
Firmware sources are included with the project. The code contains comments so it will not be difficult to change the functionality. The program is written in Eclipse, but the code compiles without any changes in AVR Studio. The MK operates from an internal oscillator at a frequency of 8 MHz. Fuses are set like this:
And in hexadecimal like this: HIGH: D9, LOW: D4
Also included are boards with bugs corrected:
This clock operates for a month. No problems were identified in the work. The LM7805 regulator and converter transistor are barely warm. The transformer heats up to 40 degrees, so if you plan to install the watch in a case without ventilation holes, you will have to use a higher power transformer. In my watch it provides a current of around 200mA. The accuracy of the movement is highly dependent on the quartz used at 32.768 KHz. It is not advisable to install quartz purchased in a store. The best results were shown by quartz from motherboards and mobile phones. Add tags
In the last century, gas-discharge indicators were used very actively on many devices: in watches, measuring equipment, frequency meters, oscilloscopes, scales and many others. Over time, they were replaced by liquid crystal displays, the manufacturing technology of which is simpler and less expensive, and most importantly, they are more compact and have a larger number of digits. Liquid crystal displays make it possible to display readings with greater accuracy.
Scope of application today
Nowadays the industry no longer makes gas-discharge indicators with numbers, but at one time they were churned out so many that they are still collecting dust in warehouses and private stocks. They can already be called antiques, just like, for example, many homes have vintage candlesticks that are used as a decorative element of the interior. Likewise, clocks with gas-discharge lamps fascinate with their illumination and are an excellent addition to the interior of various rooms, especially those furnished in a retro style.
The thing is beautiful and useful, but, alas, it is no longer produced in factories. You can make them yourself or buy ready-made ones from people who specialize in their production. Many clock circuits have been developed using gas-discharge indicators on old and new microcircuits. Let's consider the simplest options.
Watch assembly steps
First, you need to understand the operating principle of IN-14 indicator elements; practically these are neon light bulbs with a group of cathodes in the form of numbers. Depending on the power supply, one or another cathode glows alternately; the principle of an incandescent lamp with a gas-discharge process is used.
The service life of such indicators is enormous, because there is no long-term and heavy load on one cathode. For full illumination, a voltage of at least 100 V is required, so let’s start the design with a power source.
power unit
The option with a transformer, the secondary winding of which will have 170 or 180 V, is immediately excluded due to its large dimensions and weight. Selecting iron, wires and winding yourself is a thankless and tedious task. It is more practical to use a voltage converter on the MC34063 chip, which has small dimensions, weight and stable parameters.
All elements are mounted on a printed circuit board; after assembly, in most cases, no adjustment is required; with 10–12 V, the converter produces 175–180 V. As you can see, there is a transformer in the circuit, but it is very small and easily accessible for quick self-production; one can be purchased at retail networks. At the output of the secondary winding, 9–12 VAC goes to the diode bridge (rectifier). The linear stabilizer LM7805 is designed to power the electronic elements of watches.
Circuit for turning on lamps
This circuit solves the problem of matching the control voltage on the 5 V microcircuit and the controlled supply voltage of the anodes. A positive potential of 180 V is applied to the anode, and a negative potential is applied to the cathodes of the corresponding numbers.
The cathodes are switched on using a circuit based on the old K155ID1 microcircuit, which is powered by a voltage of 5 V, which in our case is very successful. 155-series microcircuits have been discontinued, but are not in short supply; they can easily be purchased in retail chains and radio markets. In order not to solder a microcircuit to each lamp, the cathode control circuit is made according to a dynamic principle.
Now the power supply, cathode and anode control circuit must be connected to the DS1307 clock processor; the Mega8 microcontroller is ideal for coordination.
Watch with controller and control buttons
This scheme includes:
- watch DS1307;
- Mega8 controller;
- DS18B20 digital thermometer;
- transistors for LED backlighting;
- buttons to control time settings.
If necessary, this circuit can be significantly simplified by removing the LED backlight, digital thermometer and lamps for discharging seconds with cathode and anode control elements.
Microcontroller firmware
The software for the clock from gas-discharge indicator lamps is written in Eclipse, transmitted without distortion to AVR Studio, codes with comments, which greatly simplifies the process. 
As a result of the firmware, certain modes and the process of managing them are installed. When you briefly press the “MENU” button, the following modes are displayed in a circle:
- mode No. 1 – time (displayed constantly);
- mode No. 2 – 2 min. time, 10 sec. date of;
- mode No. 3 – 2 min. time, 10 sec. temperature;
- mode No. 4 – 2 min. time, 10 sec. date and 10 sec. temperature;
- The time and date setting mode is set by holding the “MENU” button;
- a short press on the “UP” button (2 seconds) displays the date, holding this button turns the backlight off or on;
- short press “DOWN” (2 sec.) displays the temperature;
- brightness reduction by hourly program from 00.00 to 7 am.
Connection of main elements and operating features
Ultimately, the entire system consists of three printed circuit boards:
- Power supply, voltage converter on base MC34063
- Board with controller Mega8 and DS1307 watch
For compactness, the board is made with a double-sided arrangement of elements; this version of printed circuit boards is not a dogma; there are others. When the clock, control of the cathodes and anodes are mounted on one board, and the power supply on another, smaller lamps - IN-8 - are used to discharge seconds. Sometimes the lamps are placed on a separate panel and a two-level design is made; on the first level there is a board with a clock microcircuit and elements for controlling the cathodes and anodes. At the second level there is a board with panels for lamps; everything depends on the developer’s imagination.
IN-14 lamps are no longer in production; there may be a problem with purchasing panels for them. In this case, you can use the contacts of D-SUB connectors of the “female” format or collet rulers that match the diameter.
The plastic of the ruler can be carefully crushed with pliers and the contacts can be removed, which are soldered into the drilled holes on the printed circuit board.
Now all that remains is to pack this structure into a case (the simplest option is a rectangular box). The material can be very varied: plastic, plywood, covered with leather or other decorative material.
The power supply transformer heats up by no more than 40 °C, so it is recommended to make ventilation holes in the case to ensure a stable current of 200 mA. The accuracy of the clock depends on the stable operation of 32.768 KHz quartz, which is recommended to be taken from PC motherboards or cell phones, since low-quality products are often found in retail chains.
This method of making watches using gas-discharge lamps can be carried out by a person who has certain knowledge in electronics and practical skills. Beginners can use the services of the site http://vrtp.ru/index.php?showtopic=25695. You can order ready-made printed circuit boards for 800 rubles with detailed instructions that specify what to solder and where. For 2,500, a complete “Do it yourself” kit is sold, on lamps with a stitched microcircuit and other parts. You can buy a ready-made watch for 3,500 rubles, but this is not interesting if you want to assemble something with your own hands.
Using gas discharge indicators, you can make a very interesting Nixie Clock. In this regard, a person has many opportunities. It is possible to use a wide variety of circuits for watches. Additionally, creative people can think of interesting watch designs.
Some believe that they have many disadvantages, and therefore it is better to use luminescent analogues, but this is a misconception. In the first case, a person receives a material that works stably and does not overheat too much. While fluorescent lamps burn out quite quickly, which is a serious problem.
Important watch elements on indicators
If you do not take into account the device body and the indicators themselves, then the main part is the microcircuit. This is what allows devices to display real time. Additionally, the model includes transistors and capacitors. Power supplies mainly use batteries. Not all watches with gas-discharge indicators are equipped with transformers, as well as inductors.
How to assemble a watch with CB303 transistors?
Clocks on gas-discharge indicators, the set of CB303 transistors includes a bipolar type. First of all, it should be noted that they practically do not overheat during operation. If we talk about gas-discharge lamps, then it is important to use new ones from the store. Otherwise, they will last very little time in hours. Contacts are most often used to indicate numbers.
The control microcircuit is usually used in the K15554 series, and it belongs to the three-channel class; it has two outputs to the power supply. Wristwatch capacitors on gas-discharge indicators are mainly used with a low capacity. In some cases, stabilizers can be found in devices. In this situation, the load on the transistors will be significantly removed. It is quite possible to use a regular box as a case.
Diagram of devices with stabilizers
The circuitry of clocks based on gas-discharge indicators with stabilizers must necessarily include pulse converters. They are needed in devices in order to transmit a signal from the microcircuit. The standard circuit for clocks on gas-discharge indicators assumes capacitors with a capacity of no more than 50 pF. Transistors, in turn, are switched on bipolar type.
If we consider systems with three capacitors, then there should be three pins on the microcircuit. Transistors must withstand a maximum resistance of 6 ohms. If we talk about the current load, it averages 74 A in hours. In this case, using double boards is highly not recommended. This is due to the fact that the output voltage will increase significantly. As a result, a person will have to install fuses.
Clock using an inductor
They can withstand a maximum load of 5 A. A power supply is very necessary for their operation. The compilation process itself is carried out in two stages. First of all, capacitors are connected to the work. In this case, they are used only of the electrolytic type. In the second stage, resistors are activated in pairs. Gas discharge indicators in this situation hold up to 50 Ohms. To protect the device, many advise using a protection system that prevents short circuits.
Models on rectifiers with IN-12B indicators
IN-12B gas-discharge indicators with rectifiers allow you to keep the frequency in the circuit at 60 Hz. Due to this, the output voltage does not exceed 15 V. Stabilizers in boards are usually used of the linear type. Protection against in this case is very important. In order for transistors to withstand high resistance, they are used with the marking PP200.
Bipolar elements in watches are, as a rule, rarely used. The boards are installed directly for the K155 series watches. Their thermal conductivity is quite good and in general they have excellent characteristics. Converters are used quite rarely in the system. In principle, resistors do not need cooling, and this is a plus. In this situation, gas-discharge indicators maintain a resistance of up to 50 ohms.
Options with temperature sensors
Clocks on gas-discharge indicators allow you to monitor the main elements in the circuit. As a rule, it is very difficult to calculate the thermal load on a specific pair of resistors in advance. As a result, the installed fuse may not save the situation. Transformers also suffer from increased temperature in the clock. When high voltage is applied to the secondary winding, its integrity may be compromised.
Clocks using converters
The most common converters used in watches are the most common ones. In this case, they allow you not to install a transformer in the device. However, there are also disadvantages in this case, and they should be taken into account. First of all, the disadvantage of converters is the high input voltage, which can sometimes exceed 16 V. Coordination of all levels in such a situation becomes much more difficult.
Switching of cathodes can be carried out with a small delay. All these problems can be solved using microcontrollers. Experts advise using them specifically from the Mega 8 series. To adjust the watch you only need three buttons. Some people find it difficult to choose LEDs before starting assembly. Today, elements with red color are considered to be the most suitable. In the end, they will look simply amazing in the apartment. For numbers in gas-discharge lamps, as always, contacts are used.
Ventilation system in devices
The ventilation system in the watch may be different. The easiest way to cool device makers is considered to be natural ventilation using holes on the case. You can do them on both sides at once. It is important to understand that it is the converter that overheats the most in a watch. Taking this into account, it is highly not recommended to cover it with a board in the case. If we consider models with 15 V power supplies, then the maximum temperature of the converters there will be approximately 40 degrees. This is normal and there is no need to equip the Nixie Clock with a cooler.
Clock circuit with internal oscillators
Circuits based on gas-discharge indicators with internal generators require the use of 30 V power supplies. In this case, the internal resistance will increase to 2 Ohms. The maximum load on the transistors is 5 A. To select the clock signal, you need to use microcontrollers. The accuracy of the current flow depends solely on the quartz. Transistors are simple circuits on gas-discharge indicators, as a rule, of the bipolar type.
Temperature sensors are installed quite rarely. This is explained by the fact that the system absolutely does not need a transformer with a secondary winding. As a result, thermal conductivity will be quite low. Anode keys for ports are used. They are only suitable for boards with three connectors. Microcontrollers of the Mega 8 series will be appropriate in this case. To flash the board firmware, a high monitoring threshold is required.
Clock on PP22 capacitors
Clocks on gas-discharge indicators on capacitors of this type allow for more stable signal transmission. The monitoring threshold in this case will be quite high. Resistors in watches are used only with a resistance of at least 6 ohms. The input voltage must be at least 6 V. Level matching occurs only by switching the cathodes.
Converters for capacitors of this type are suitable for the “Step Up” series. Additionally, you should take care of the protection system to prevent short circuits. Microcircuits for capacitors are used only for two outputs. In this case, there can be up to five ports. Stabilizers for capacitors are mainly used in the linear class. The input must be at least 5 V.
Are there watches with two chips?
Clocks with gas-discharge indicators with two microcircuits are quite rare today. They are necessary for faster process synchronization. In this case, the lamp cathodes are switched in a matter of nanoseconds. cannot be used for such watches. The minimum resistance level in this case should be at 50 Ohms.
In turn, transistors are required to withstand a current voltage of 30 A. Converters in watches, as a rule, are installed of the pulse type. Due to this, switching to binary format occurs quickly. Direct coordination of levels occurs in the microcontroller. You can regulate the voltage in the device using a stabilizer. However, the minimum should be 22 pF.
Models with KA445 fuses
These fuses are of electrolytic type. They have a maximum capacitance of exactly 10 pF. At the beginning of the circuit, they are usually located in front of the transistors. It is important to use LEDs in watches with high bandwidth. The chip must have at least three ports. In this case, a linear type stabilizer must be soldered. A fuse will help deal with high input voltage to a large extent.
If you exclude the use of a converter in a watch, you can use a transformer with a secondary winding. It is installed in front of the power supply. Experts advise using fuses only of the fusible type. They will last quite a long time in the watch. It is important to install resistors in front of the quartz with a limit of 33 Ohms. The power supply must be designed for 15 V. As a result, the maximum frequency in the system will fluctuate around 60 Hz.
This article will focus on making original and unusual watches. Their uniqueness lies in the fact that the time is indicated using digital indicator lamps. Once upon a time, a huge number of such lamps were produced, both here and abroad. They were used in many devices, from watches to measuring equipment. But after the advent of LED indicators, the lamps gradually fell out of use. And so, thanks to the development of microprocessor technology, it became possible to create watches with a relatively simple circuit using digital indicator lamps.
I think it would not be amiss to say that mainly two types of lamps were used: fluorescent and gas-discharge. The advantages of luminescent indicators include low operating voltage and the presence of several discharges in one lamp (although such examples are also found among gas-discharge indicators, but they are much more difficult to find). But all the advantages of this type of lamp are offset by one huge disadvantage - the presence of a phosphor, which burns out over time, and the glow dims or stops. For this reason, used lamps cannot be used.
Gas discharge indicators are free from this drawback, because a gas discharge glows in them. Essentially, this type of lamp is a neon lamp with multiple cathodes. Thanks to this, the service life of gas-discharge indicators is much longer. In addition, both new and used lamps work equally well (and often used ones work better). However, there are some drawbacks - the operating voltage of gas-discharge indicators is more than 100 V. But solving the problem with voltage is much easier than with a burn-out phosphor. On the Internet, such watches are common under the name NIXIE CLOCK:
The indicators themselves look like this:
So, everything seems clear about the design features, now let’s start designing the circuit of our watch. Let's start by designing a high-voltage voltage source. There are two ways here. The first is to use a transformer with a secondary winding of 110-120 V. But such a transformer will either be too bulky, or you will have to wind it yourself (the prospect is so-so). Yes, and voltage regulation is problematic. The second way is to assemble a step up converter. Well, there will be more advantages: firstly, it will take up little space, secondly, it has short-circuit protection and, thirdly, you can easily adjust the output voltage. In general, there is everything you need to be happy. I chose the second path, because... I had no desire to look for a transformer and winding wire, and I also wanted something miniature. It was decided to assemble the converter on MC34063, because I had experience working with her. The result is this diagram:
It was first assembled on a breadboard and showed excellent results. Everything started immediately and no configuration was required. When powered by 12V. the output turned out to be 175V. The assembled power supply of the watch looks like this:
A linear stabilizer LM7805 was immediately installed on the board to power the clock electronics and a transformer.
The next stage of development was the design of the lamp switching circuit. In principle, controlling lamps is no different from controlling seven-segment indicators, with the exception of high voltage. Those. It is enough to apply a positive voltage to the anode and connect the corresponding cathode to the negative supply. At this stage, two tasks need to be solved: matching the levels of the MK (5V) and lamps (170V), and switching the cathodes of the lamps (they are the numbers). After some time of thought and experimentation, the following circuit was created to control the anodes of the lamps:
And controlling the cathodes is very easy; for this they came up with a special K155ID1 microcircuit. True, they have long been discontinued, like lamps, but buying them is not a problem. Those. to control the cathodes, you just need to connect them to the corresponding pins of the microcircuit and submit data in binary format to the input. Yes, I almost forgot, it is powered by 5V. (well, a very convenient thing). It was decided to make the display dynamic, because otherwise, you would have to install K155ID1 on each lamp, and there will be 6 of them. The general scheme turned out like this:
Under each lamp I installed a bright red LED (it’s more beautiful this way). When assembled, the board looks like this:
We couldn’t find sockets for the lamps, so we had to improvise. As a result, the old connectors, similar to modern COM, were disassembled, the contacts were removed from them, and after some manipulations with wire cutters and a file, they were soldered into the board. I didn’t make panels for the IN-17, I did them only for the IN-8.
The hardest part is over, all that remains is to develop a circuit for the “brain” of the watch. For this I chose the Mega8 microcontroller. Well, then everything is quite easy, we just take it and connect everything to it in the way that is convenient for us. As a result, the clock circuit included 3 buttons for control, a DS1307 real-time clock chip, a DS18B20 digital thermometer, and a pair of transistors for controlling the backlight. For convenience, we connect the anode keys to one port, in this case it is port C. When assembled, it looks like this:
There is a small error on the board, but it has been corrected in the attached board files. The connector for flashing the MK is soldered with wires; after flashing the device, it should be unsoldered.
Well, now it would be nice to draw a general diagram. No sooner said than done, here it is:
And this is what it all looks like assembled:
Now all that remains is to write the firmware for the microcontroller, which is what was done. The functionality turned out to be as follows:
Display time, date and temperature. When you briefly press the MENU button, the display mode changes.
Mode 1 - time only.
Mode 2 - time 2 min. date 10 sec.
Mode 3 - time 2 min. temperature 10 sec.
Mode 4 - time 2 min. date 10 sec. temperature 10 sec.
When held, the time and date settings are activated, and you can navigate through the settings by pressing the MENU button.
The maximum number of DS18B20 sensors is 2. If the temperature is not needed, you can not install them at all; this will not affect the operation of the watch in any way. There is no provision for hot plugging of sensors.
Briefly pressing the UP button turns on the date for 2 seconds. When held, the backlight turns on/off.
By briefly pressing the DOWN button, the temperature is turned on for 2 seconds.
From 00:00 to 7:00 the brightness is reduced.
The whole thing works like this:
Firmware sources are included with the project. The code contains comments so it will not be difficult to change the functionality. The program is written in Eclipse, but the code compiles without any changes in AVR Studio. The MK operates from an internal oscillator at a frequency of 8 MHz. Fuses are set like this:
And in hexadecimal like this: HIGH: D9, LOW: D4
Also included are boards with bugs corrected:
This clock operates for a month. No problems were identified in the work. The LM7805 regulator and converter transistor are barely warm. The transformer heats up to 40 degrees, so if you plan to install the watch in a case without ventilation holes, you will have to use a higher power transformer. In my watch it provides a current of around 200mA. The accuracy of the movement is highly dependent on the quartz used at 32.768 KHz. It is not advisable to install quartz purchased in a store. The best results were shown by quartz from motherboards and mobile phones.
