March 9, 2009 at 3:23 pmLarge street clock
All the same, not the habraeffect does not allow itself to be forgotten. An article on how to make a large watch that can be hung on a building. Copied to Habr. the server is not able to digest so many visitors.
Recently, large electronic clocks began to appear on many buildings. This article will discuss how to assemble such a watch yourself. It will also indicate where the author stepped on the rake and where to pay attention.
First of all, you should decide on the size of the watch and budget. Estimate the rough energy consumption of components, architecture. Make a dynamic display or control each digit individually. Which and in what quantities to use LEDs. What material to make the body of.
So, the finished watch turned out like this:
Dimensions: 630x235x105
Weight: 5.8 kg
Power consumption: 30 W
Stroke accuracy is not worse than ± 1 min per month.
Unfortunately, the designer’s flight of imagination limits the range of stores sold and the tools available. The watch case was made of an aluminum corner bought in OBI, and the sides were made of plexiglass craftsman bought in a store. The digit boards were made of polystyrene. All seams for tightness are coated with transparent plumbing silicone sealant.
Why were the side walls made of plexiglass and not polystyrene? The fact is that polystyrene, as it turned out, is not resistant to atmospheric influences, and after 2 years it would simply be stricken, while plexiglass was more resistant in this regard. Since the clock hangs on the street, it is advisable to make it airtight. At the same time, consider the heat dissipation of the components so that they do not suffocate in the summer in the sun. Ideally, before they are completely screwed in, throw a bag of silica gel inside so that moisture does not condense from the inside in cold weather. Use components of industrial design (from -50 to +60 degrees). Coat the finished circuit board with varnish from corrosion, which can easily gnaw through thin conductors. Fasten the components firmly inside, if the cables will hang when carrying inside, then the contact will be broken at one point.
After the frame was made, plexiglass was cut and the whole thing was assembled, the turn of numbers begins. 4 digits were made of segments, 22 LEDs each, + 2 dots of 4 LEDs, total 624 LEDs. Green LEDs with matte housing L-53SGD. This is where the first mistake lies. I chose the LEDs based on the viewing angle, which is maximum for the LEDs in the matte case, but at the same time their light output is small. As a result, it turned out that the LEDs are perfectly visible in the room, but on the street only in cloudy weather. Therefore, I strongly recommend that you fork out, buy 4-5 LEDs of each brand, start them from the battery, go outside and evaluate how they will be seen, how blind they are in the sun, what is the viewing angle.
Current through a 20 mA LED for datasheet. They are assembled in chains of 2 in series to minimize losses on current-limiting resistors (loss of efficiency and excessive heating we do not need). It turns out that the ignited current is 1.1 A. Here lies the important point of choosing an architecture. Can you make a PSU that will produce 4.4 A and will calmly survive the inrush current at 100% of the load - do an individual control of each digit. Luminous efficiency will be maximum. You can not (for example, there is no transformer of sufficient power on sale) - make the indication dynamic. The brightness will be lower.
The power supply is better done according to the classical scheme (transformer, diode bridge, smoothing capacitor) than a pulse one - in the first place, the fewer parts the higher the reliability, and in the second such PSU is more unpretentious. (The clock worked when I lowered the voltage to 110V by the LATR. The LEDs went out, but the passage of time did not stop).
The next stage is the development of control electronics. The clock is assembled on an ATMEGA16 microcontroller, with an external quartz resonator connected to the TOSC pins, which allows you to count the time. The accuracy of the watch depends only on the accuracy of the quartz, respectively, and the watch as a result is quartz.
The watch consists of 3 boards. The first board contains a transformer with a power supply and a microcontroller. The second one is a voltage converter, increases 5 V to 12 V (it is necessary to power the MOSFET keys, because of the voltage drop on the LEDs, five volt logic levels with MK are not enough to unlock the transistor. The converter with a cascade of amplifiers transistors solved this problem.) The third board is keys with current limiting resistors. All boards are interconnected by connectors - this is incredibly convenient in the process of debugging and assembly.
The aluminum cylinder is a 6.3V and 100,000uF capacitor. Probably the only domestic electronic component manufactured by the USSR. Since the clock does not have circuits inside to save time, in the event of a power outage, this capacitor can survive dips in the supply voltage for up to 4 seconds.
A lot of nerves spoiled the bug, which took almost 3 months to catch. A 0.1 μF blocking capacitance was not established for the power supply between the legs of the microcontroller, which caused very interesting malfunctions that looked like electromagnetic pickups, and judging by the oscillograms, a software malfunction.
A thermometer was added to the watch - a DS1620 temperature sensor with connection via an i2c bus. And here is the rake number two. The fact is that inside the watch, when working, everything gets warm. The diode bridge is especially hot, besides the clock hangs on the pavilion, which also heats up when students go through it. As a result, the temperature sensor fixed in the coldest place of the watch gave an error of 5 degrees (when it was -15 on the street). Make a remote sensor.
The clock program is quite simple - a millisecond counter for interruption. Functions for calculating a leap year (within 2000-2100 years), automatic transition to winter / summer time, settings, set time correction constant (seconds per day), set time for displaying time / temperature.
If I were to make a second instance, I would fix it:
1) I would use a specialized real-time clock chip with my battery.
2) I would use other LEDs in a transparent case
3) A connector for connecting an external temperature sensor.
A very interesting idea is to make time synchronization with GPS. This watch has 3 buttons for setting. Many companies complete their watches with a remote control to set the time.
Remember that someone will repair the watch, so putting an idea into a piece of paper with a circuit is a very good idea.
In total, the watch cost 5,000 rubles. They were posted on the building of the forest engineering faculty of Ural State Technical University. We calmly survived the January frosts of -30 degrees. While the flight is normal. Below are photos, looking at which is much more interesting than reading the text)
Images. Not all but basic:
Original article here: licrym.org/index.php/%D0%91%D0%BE%D0%BB%D1%8C%D1%88%D0%B8%D0%B5_%D1%83% D0% BB% D0% B8% D1% 87% D0% BD% D1% 8B% D0% B5_% D1% 87% D0% B0% D1% 81% D1% 8B You
can ask questions about the hours in the comments.
Recently, large electronic clocks began to appear on many buildings. This article will discuss how to assemble such a watch yourself. It will also indicate where the author stepped on the rake and where to pay attention.
First of all, you should decide on the size of the watch and budget. Estimate the rough energy consumption of components, architecture. Make a dynamic display or control each digit individually. Which and in what quantities to use LEDs. What material to make the body of.
So, the finished watch turned out like this:
Dimensions: 630x235x105
Weight: 5.8 kg
Power consumption: 30 W
Stroke accuracy is not worse than ± 1 min per month.
Unfortunately, the designer’s flight of imagination limits the range of stores sold and the tools available. The watch case was made of an aluminum corner bought in OBI, and the sides were made of plexiglass craftsman bought in a store. The digit boards were made of polystyrene. All seams for tightness are coated with transparent plumbing silicone sealant.
Why were the side walls made of plexiglass and not polystyrene? The fact is that polystyrene, as it turned out, is not resistant to atmospheric influences, and after 2 years it would simply be stricken, while plexiglass was more resistant in this regard. Since the clock hangs on the street, it is advisable to make it airtight. At the same time, consider the heat dissipation of the components so that they do not suffocate in the summer in the sun. Ideally, before they are completely screwed in, throw a bag of silica gel inside so that moisture does not condense from the inside in cold weather. Use components of industrial design (from -50 to +60 degrees). Coat the finished circuit board with varnish from corrosion, which can easily gnaw through thin conductors. Fasten the components firmly inside, if the cables will hang when carrying inside, then the contact will be broken at one point.
After the frame was made, plexiglass was cut and the whole thing was assembled, the turn of numbers begins. 4 digits were made of segments, 22 LEDs each, + 2 dots of 4 LEDs, total 624 LEDs. Green LEDs with matte housing L-53SGD. This is where the first mistake lies. I chose the LEDs based on the viewing angle, which is maximum for the LEDs in the matte case, but at the same time their light output is small. As a result, it turned out that the LEDs are perfectly visible in the room, but on the street only in cloudy weather. Therefore, I strongly recommend that you fork out, buy 4-5 LEDs of each brand, start them from the battery, go outside and evaluate how they will be seen, how blind they are in the sun, what is the viewing angle.
Current through a 20 mA LED for datasheet. They are assembled in chains of 2 in series to minimize losses on current-limiting resistors (loss of efficiency and excessive heating we do not need). It turns out that the ignited current is 1.1 A. Here lies the important point of choosing an architecture. Can you make a PSU that will produce 4.4 A and will calmly survive the inrush current at 100% of the load - do an individual control of each digit. Luminous efficiency will be maximum. You can not (for example, there is no transformer of sufficient power on sale) - make the indication dynamic. The brightness will be lower.
The power supply is better done according to the classical scheme (transformer, diode bridge, smoothing capacitor) than a pulse one - in the first place, the fewer parts the higher the reliability, and in the second such PSU is more unpretentious. (The clock worked when I lowered the voltage to 110V by the LATR. The LEDs went out, but the passage of time did not stop).
The next stage is the development of control electronics. The clock is assembled on an ATMEGA16 microcontroller, with an external quartz resonator connected to the TOSC pins, which allows you to count the time. The accuracy of the watch depends only on the accuracy of the quartz, respectively, and the watch as a result is quartz.
The watch consists of 3 boards. The first board contains a transformer with a power supply and a microcontroller. The second one is a voltage converter, increases 5 V to 12 V (it is necessary to power the MOSFET keys, because of the voltage drop on the LEDs, five volt logic levels with MK are not enough to unlock the transistor. The converter with a cascade of amplifiers transistors solved this problem.) The third board is keys with current limiting resistors. All boards are interconnected by connectors - this is incredibly convenient in the process of debugging and assembly.
The aluminum cylinder is a 6.3V and 100,000uF capacitor. Probably the only domestic electronic component manufactured by the USSR. Since the clock does not have circuits inside to save time, in the event of a power outage, this capacitor can survive dips in the supply voltage for up to 4 seconds.
A lot of nerves spoiled the bug, which took almost 3 months to catch. A 0.1 μF blocking capacitance was not established for the power supply between the legs of the microcontroller, which caused very interesting malfunctions that looked like electromagnetic pickups, and judging by the oscillograms, a software malfunction.
A thermometer was added to the watch - a DS1620 temperature sensor with connection via an i2c bus. And here is the rake number two. The fact is that inside the watch, when working, everything gets warm. The diode bridge is especially hot, besides the clock hangs on the pavilion, which also heats up when students go through it. As a result, the temperature sensor fixed in the coldest place of the watch gave an error of 5 degrees (when it was -15 on the street). Make a remote sensor.
The clock program is quite simple - a millisecond counter for interruption. Functions for calculating a leap year (within 2000-2100 years), automatic transition to winter / summer time, settings, set time correction constant (seconds per day), set time for displaying time / temperature.
If I were to make a second instance, I would fix it:
1) I would use a specialized real-time clock chip with my battery.
2) I would use other LEDs in a transparent case
3) A connector for connecting an external temperature sensor.
A very interesting idea is to make time synchronization with GPS. This watch has 3 buttons for setting. Many companies complete their watches with a remote control to set the time.
Remember that someone will repair the watch, so putting an idea into a piece of paper with a circuit is a very good idea.
In total, the watch cost 5,000 rubles. They were posted on the building of the forest engineering faculty of Ural State Technical University. We calmly survived the January frosts of -30 degrees. While the flight is normal. Below are photos, looking at which is much more interesting than reading the text)
Images. Not all but basic:
Original article here: licrym.org/index.php/%D0%91%D0%BE%D0%BB%D1%8C%D1%88%D0%B8%D0%B5_%D1%83% D0% BB% D0% B8% D1% 87% D0% BD% D1% 8B% D0% B5_% D1% 87% D0% B0% D1% 81% D1% 8B You
can ask questions about the hours in the comments.