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Every digital clock has a crystal inside it to keep track of time. This crystal is not only present in the clock but also present in all computing real-time systems. This crystal generates clock pulses, which is needed for timing calculations. Although there are some other ways to get clock pulses for higher accuracy and frequency, but the most preferred way is to use crystal to keep track of time. Here we will DS3231 RTC IC to build an Atmega16 based Digital Wall Clock. DS3231 RTC has a highly accurate crystal inside it, so no external Crystal oscillator is needed. In this Digital Clock Project, ten common anode 7-segment displays of 0.8-inch are used to display time and date. Here seven segment displays are used to show hour, minute, date, month and year. Our PCB design also has options to display seconds and temperature, which can be displayed by adding more display units. Circuit Diagram and Explanation There are two parts of this Digital Wall Clock Circuit, one is display part which has 5 pairs of 7-segments on five different PCB boards and another is controlled Unit part which is responsible for fetching time from RTC chip and send that data and time to 7-segment display. As we have used 10 seven segment displays so we cannot connect each display with a separate IO port. So here multiplexing technique is used to connect multiple seven segments using fewer pins of microcontroller. LED pins a,b,c,d,e,f,g,h of seven segment display is connected to PORTB of atmega16 parallel. Here we have used 10 seven segment displays so we need 10 control pins which are connected at PORTD, PORTA and PORTC. RTC DS3231 having an internal crystal is connected to PORTC’s SDA and SCL pin because this chip works on I2C communication. Interfacing method of this chip is the same as DS1307. We have used DS1307 with Arduino, Raspberry Pi and 8051 MCU. Same code can be used for both DS3231 and DS1307. For one display board, two seven segment displays and 2 LED are used. So here we have five different display boards to display Time in Hours and minute (HH-MM), and date in DD-MM-YY. PCB Design and fabrication for the Digital Clock For this Atmega16 based wall clock project, we have designed two PCBs. One is for Control unit which is used to control all the operations of the project and second part is for displaying the time and date on seven segment displays. Display part contains five pairs of 0.8 inches seven segment display. So by assembling 5 pieces we have the complete Digital Clock. To multiplex 7-segment displays, Data line of the 5 PCBs will be connected to the same port of control unit and control line is connected different pin of the control unit. Below are the top and bottom views of PCB layouts of one Display board which consists two seven segment displays: Below are the top and bottom views of Control Unit PCBs Ordering the PCB using PCBGoGo There are many PCB fabrication services are available online, but as I used PCBGoGo previously in one of my other projects, I found it cheap and hassle-free as compared to other vendors. Here are the steps to order PCB from PCBGoGo: Step 1: Get into www.pcbgogo.com, sign up if this is your first time. Then, in the PCB Prototype tab enter the dimensions of your PCB, the number of layers and the number of PCB you require. Step 2: Proceed by clicking on the Quote Now button. You will be taken to a page where to set few additional parameters if required like the material used track spacing etc. But mostly the default values will work fine. The only thing that we have to consider here is the price and time. As you can see the Build Time is only 2-3 days and it just costs only $5 for our PSB. You can then select a preferred shipping method based on your requirement. Step 3: The final step is to upload the Gerber file and proceed with the payment. To make sure the process is smooth PCBGOGO verifies if your Gerber file is valid before proceeding with the payment. This way you can sure that your PCB is fabrication friendly and will reach you as committed. Now PCBGoGo will take some time around 10 min to 1 Hour to review your Gerber file. After completion of the review, you can proceed with the payment. Assembling the PCB After the board was ordered, it reached me after some days though courier in a neatly labeled well packed box and like always the quality of the PCB was awesome. I am sharing few pictures of the boards below for you to judge. I turned on my soldering rod and started assembling the Board. Since the Footprints, pads, vias and silkscreen are perfectly of the right shape and size I had no problem assembling the board. The board was ready in just 10 minutes from the time of unpacking the box. Few pictures of the board after soldering are shown below. Testing the Digital Clock Complete code is given at the end of this tutorial, just connect the PCBs as shown in the circuit diagram and upload the code into Atmega16. And you will see time and date appearing on the ten Seven segments displays.
Well, here are several very interesting circuits : Remote Control Blocker by IR More than once we will have spent watching the best scene of a strip and that we change the channel. To avoid these little surprises that we do not like so much we have this powerful team that will be in charge of "flooding" with IR signal the enclosure avoiding that the remote control of the TV or the equipment that was working properly. The circuit is more than simple, the PNP transistor oscillates at the appropriate frequency of the equipment to be blocked while the NPN transistor amplifies the voltage to apply it on the IR diodes. These diodes should be high performance for a better result.Adjustme Place yourself near the equipment to block and operate the equipment, turn the preset to find the frequency that prevents the operation of the original remote control. -------------------------------------------------- ---------------------------------------- TV transmitter This sensillo circuit allows to transmit the signal of a videotape or camera around the perimeter of a medium-sized house. It is very practical, for example, when you have a satellite television system and only one tuner / decoder is available. The same applies to boxes for premium channels of cable TV operators. Although it is also useful when you want to transmit the video signal from security cameras to hard-wired points. The scheme is very simple. The variable capacitor acts as a tuner, allowing you to adjust the frequency (channel) where you want to broadcast. Given the low power of this system the antenna can be a simple cable about 30 cm long or a retractable antenna. The transformer T1 is formed in its primary by 7 turns of wire while its secondary is composed of 18 turns. The 220pF capacitor connected in parallel with the secondary must be incorporated into the transformer last. This type of transformer is called SIF. As for the coil L1, this should be formed on a ferrite core of 3mm and on it should wind 4 turns of wire. Since this system operates with a very low power license is not required to use it, but if it were to place power stages that increase the scope of the set we recommend you to become a lawyer and become familiar with the legal aspects in force depending on the region where you go to use. Keep in mind that a poorly calibrated power stage could cause interference in the reception equipment of neighboring houses. Be careful in the assembly and calibration of this type of equipment. -------------------------------------------------- ---------------------------------------- 2w FM transmitter This transmitter is ideal for jealous girlfriends. Simply put it inside a teddy bear and give it to the poor boyfriend. Then, from a distance of approx. 300 meters depending on the complexity of the place, you can listen to transmissions with a conventional FM receiver. As long as the boyfriend does not listen to himself on a walkman, all is well. The truth is that, beyond the use that is given, this transmitter uses only two common transistors to broadcast audio through the commercial FM band. It is quite stable and the signal quality is sufficient to transmit musical or spoken audio. 30-40 MHz L = 8 turns on a ferrite core of 0.25 " Cx = trimmer of 15-20 pF Cy = trimmer of 10-15 pF Antenna = Wire of 38" 40-50 MHz L = 6.75 turns on a ferrite core of 0.25 " Cx = trimmer of 10-20 pF Cy = trimmer of 10-15 pF Antenna = Wire of 37" 90-100 MHz L = 6.5 turns on a ferrite core of 0.25 " Cx = capacitor of 5.6 pF Cy = capacitor of 3.3 pF Antenna = Wire of 20 " The circuit must be assembled on an epoxy printed circuit and powered with 9 or 12 v DC. It consumes 4w, of which 2w makes them irradiated power and the other two makes them heat. If you want to use the system with an electret type microphone, you will have to add a resistance of 1K from the positive to the negative terminal of the input capacitor (base of 2N3708), establishing the power that type of microphones require. Given its reduced power this type of devices do not require state authorization to operate. -------------------------------------------------- ---------------------------------------- 55w car amplifier Up to now, all the auto power circuits required a voltage source since these devices needed more than 40 volts. This circuit breaks with that tradition making it possible to manufacture a good quality audio amplifier for the car with only one integrated circuit per audio channel. In this way to make a stereo unit will suffice with two integrated and to make it quadraphonic will have to use four. As you can see in the diagram, the chip has everything necessary in its capsule, so it only remains to place the capacitors and filter and control resistors. Since the system is of the bridge type, the two speaker terminals are amplified, so none of them should be placed to ground. In any case, the circuit is protected against costs at the start, in addition to a long list of other protections. It is configured in class H. For more information about this chip connect to the page of Philips electronics, whose link is available in another section of this portal. The audio output does not require DC blocking capacitors as well as typical RL sets in these projects. It is possible to add a MUTE function which we omit in the diagram to simplify it to the maximum. If you want to do it, you have to place a 1K resistor between the ground and terminal 4, leaving the components that are as is. Thus the circuit goes into a mute state. By removing said resistor, the circuit returns to normal operation. Consult the specification sheet for more information about it. As in all these projects, heat sinks are extremely critical. Poor dissipation will cause the circuit to overheat and this will cause the system to shut down. It is not going to ruin because the chip includes internal thermal protection, but it will shut down causing it to stop amplifying. A Slot-1 or Slot-A microprocessor and fan (such as the AMD K7 or Intel Pentium III) is suitable, as long as the fan motor is running. In the case of using this type of forced cooling, it is important to design a good air channel since the fan is useless if it has no fresh air inlet and outlet. Another way to get good heatsinks is by making the sides of the cabinet the same heatsinks. In this case the size will be adequate and, in addition, It should be noted that this small "eats" 10 amps at maximum power so the power cables must be of adequate section. Otherwise they could be cut causing short circuits in the electric circuit of the vehicle. If you are going to mount four of these modules take into account the following: A medium vehicle has a 63 amp battery. This circuit multiplied by four consumes 40 amps. It is necessary to make a simple division to determine that it is capable of unloading the battery of the car in only two hours of use at maximum power. Therefore you will have to take special care as to see where the unit is connected. Another important factor is the ignition and fuel injection system. These circuits are usually somewhat sensitive to voltage drops so this amplifier can impair its operation. An alternative (very common in these cases) is to place a second battery housed in the trunk of the vehicle, which is charged through a diode from the voltage regulator of the alternator. Even the most expert of the engineers should take a tour of an installation house for this type of equipment because "the best hunter will miss a hare" and a mistake in the installation can leave it on foot. Do not even think about connecting the amplifier's power cord to the ignition key of the vehicle directly. Not even the key of a large truck could withstand the current. The way to connect it is simple, although it requires a relay. The contacts of the relay coil go in parallel with the current radio or pass tapes of the car, while the contacts of the mechanical key of that relay go in series with the cable (thick) that brings power to the amplifier from the battery. In this way the relay makes the brute force and the ignition key must only move the coil of the electromagnet. The relay should be able to handle up to 50A. It is possible to get one like this in the auto parts houses, asking for the one that switches the general power supply of the motor or the one that drives the starter motor. Another important point of the installation is the input signal. If the tape device you have installed in the car does not have line output, you will have to make an impedance adaptation and a power reduction to be able to connect the speakers' outputs to the amplifier's audio inputs. A good way is to buy a passive equalizer which modifies the tone of each band to equalize "attenuating" the others. It is important that this equalizer does not have an amplified output, because we would be at the starting point again. Although today most CD car kits have output without amplification. Another very common way is to place audio output transformers with the 8 ohm winding connected to the stereo output and the 2000 ohm winding connected to the amplifier input. It is necessary to clarify that although 1% of total harmonic distortion seems to be too much to be in a car it is somewhat low, given that the units that are commercialized normally have indexes of 3% to 5%. Only, just as they do with power, they lie about that value. Since the chip has a protection circuit against shorts that disconnects the output when the impedance of the load falls below 0.5 ohms, placing 2 ohms speakers (or 2 of 4 ohms in parallel) would cause the power to rise to 75 watts, but distortion will also rise to almost 10%. This is not acceptable for musical sound, but for propaganda or publicity on the public highway is ideal. Of course, the current demand will also increase. very good -------------------------------------------------- ---------------------------------------- Electronic Charger for Car Batteries Whether because we leave of using the vehicle for very long periods of time or because the battery is close to running out, this circuit allows it to be properly charged and indicated by means of an LED when the process has finished. As you can see the circuit is a conventional power supply, followed by an LM338 regulator which is controlled by means of an operational amplifier that is responsible for controlling the state of the load to detect the precise moment when it must stop and operate the LED indicator. The three-stage resistive divider allows, on the one hand, to take the reference voltage for the operational amplifier and, on the other, to control the LM338 regulator by means of the output of the operational one. In this way, the load cutoff occurs when the current drops below half an ampere, when the circuit begins to oscillate causing the transistor to conduct the current to the LED making it shine to indicate the end of the load. Note that the bridge rectifier is 10 amperes (voltage equal to or greater than 50V) so it is not for soldering in printed circuit but to screw to the metallic cabinet of the equipment and connect by means of crimped terminals. The initial filtering capacitor can be soldered on the plate or it can be enclosed in the cabinet by means of two plastic seals and soldered in parallel with the positive and negative terminals of the diode bridge. The general switch is of the type used in electric coffee machines which have inside the neon gas lamp that lights up when the equipment is turned on. Pay close attention to how this switch is connected since it is very common to confuse terminals and short the 220V line. The regulator LM338 must be mounted outside the printed circuit on a suitable heat sink of not less than 10 x 10 cm of surface. If desired, a DC ammeter can be placed in series with the positive terminal of the output to the battery to visually monitor the current status of the load. This instrument can be analog or digital indistinctly, although nowadays it is much more colorful a digital one. The positive terminal of the instrument is connected to the circuit and the negative terminal goes to the battery (towards its positive terminal). The resistance of 0.1 ohm must be mounted on the plate, but raised 2 or 3 cm from it to prevent the heat from disturbing the pertinax. It is possible to place a buzzer that sounds while the LED shines. To use it, just place the battery to charge, turn on the system and press the button that starts the charge. When finished the LED will light up and the system should be turned off and the battery removed from the terminals. -------------------------------------------------- ---------------------------------------- 90W amplifier Using only four transistors in a quasi configuration -complementary this amplifier can deliver 90W of power over a load of 4 ohms and at a really low cost. http://pablin.com.ar/electron/circuito/audio/amp90/circuito.gif As you can see in the diagram, there are no expensive components in this circuit, except for the transformer of the source and the speaker. The input stage consists of two current drivers that directly excite the transistor pairs of the output stage. The latter (the 2N3055) must be mounted on generous heat sinks in order to preserve the useful life of these devices. When being fed by a simple source (of 80Vcc) to the exit of the final stage, before the speaker, a capacitor must be placed that blocks the passage to the direct current and only lets pass the audio signal. The source must be capable of providing 1.5A of current per audio channel. In this way a stereo power will require 3A to operate and one of four channels will require 6A. -------------------------------------------------- ---------------------------------------- Well, this is all, Note: maybe some of the circuits have not been tested. in case you need some other information, more circuits or something, ask for it, but here is the source, where there is more http://xenoa.co.uk/
i make a PCB order at a China website www.allpcb.com/g6 and want to have them assembled for my project. but i was told it would take about 3 weeks, for pcb fabricating and assembly for only 50 units. i am wondering why it takes so long, is it normal?