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Wednesday, November 19, 2014

Traffic Light 20 Chanel based on 74LSxx

This view of the proposed traffic Light 20 Chane based only on family and 74LSxx IC 555 as clock source. It is a digital logic circuit. To construct the traffic light rangkaian Control requires no programming of microcontrollers.

This page features a circuit that has twenty open collector outputs that turn on one at a time in a continuous sequence. The circuit make use of the family 74LSxx TTL integrated logic devices. The circuits are designed to drive light emitting diodes or low current and low voltage incandescent lamps, but can also lead to other charges of 80 milliamps.

notes:

The low output go in sequence from 1 - 0 and back to 1 -0
At the clock rate of the 555 timer
c3 = 1uf to 10uf depending on the rate of change desured
R2 (Variable resistor) in use to determine the timer

Friday, November 7, 2014

Power On Indicator

Some types of electronic equipment do not provide any indication that they are actually on when they are switched on. This situation can occur when the back-light of a display is switched off. In addition, the otherwise mandatory mains power indicator is not required with equipment that consumes less than 10 watts. As a result, you can easily forget to switch off such equipment. If you want to know whether equipment is still drawing power from the mains, or if you want to have an indication that the equipment is switched on without having to modify the equipment, this circuit provides a solution.

One way to detect AC power current and generate a reasonably constant voltage independent of the load is to connect a string of diodes wired in reverse parallel in series with one of the AC supply leads. Here we selected diodes rated at 6 A that can handle a non-repetitive peak current of 200 A. The peak current rating is important in connection with switch-on currents. An advantage of the selected diodes is that their voltage drop increases at high currents (to 1.2 V at 6 A). This means that you can roughly estimate the power consumption from the brightness of the LED (at very low power levels). The voltage across the diodes serves as the supply voltage for the LED driver. To increase the sensitivity of the circuit, a cascade circuit (voltage doubler) consisting of C1, D7, D8 and C2 is used to double the voltage from D1–D6. Another benefit of this arrangement is that both halve- waves of the AC current are used. We use Schottky diodes in the cascade circuit to minimise the voltage losses.

Circuit diagram :

Power On Indicator Circuit Diagram

The LED driver is designed to operate the LED in blinking mode. This increases the amount of current that can flow though the LED when it is on, so the brightness is adequate even with small loads. We chose a duty cycle of pproximately 5 seconds off and 0.5 second on. If we assume a current of 2 mA for good brightness with a low-current LED and we can tolerate a 1-V drop in the supply voltage, the smoothing capacitor (C2) must have a value of 1000 µF. We use an astable multivibrator built around two transistors to implement a high-efficiency LED flasher. It is dimensioned to minimise the drive current of the transistors. The average current consumption is approximately 0.5 mA with a supply voltage of 3 V (2.7 mA when the LED is on; 0.2 mA when it is off). C4 and R4 determine the on time of the LED (0.5 to 0.6 s, depending on the supply volt-age). The LED off time is determined by C3 and R3 and is slightly less than 5 seconds. The theoretical value is R × C × ln2, but the actual value differs slightly due to the low supply voltage and the selected component values.

Diodes D1-D6 do not have to be special high-voltage diodes; the reverse volt-age is only a couple of volts here due the reverse-parallel arrangement. This voltage drop is negligible compared to the value of the mains voltage. The only thing you have to pay attention to is the maximum load. Diodes with a higher current rating must be used above 1 kW. In addition, the diodes may require cool-ing at such high power levels. Measurements on D1–D6 indicate that the voltage drop across each diode is approximately 0.4 V at a current of 1 mA. Our aim was to have the circuit give a reasonable indication at current levels of 1 mA and higher, and we succeeded nicely. However, it is essential to use a good low-current LED.

Caution: the entire circuit is at AC power potential. Never work on the circuit with the mains cable plugged in. The best enclosure for the circuit is a small, translucent box with the same colour as the LED. Use reliable strain reliefs for the mains cables entering and leaving the box (connected to a junction box, for example). The LED insulation does not meet the requirements of any defined insulation class, so it must be fitted such that it cannot be touched, which means it cannot protrude from the enclosure.

Wednesday, November 5, 2014

Always on for PCs

Many enthusiasts will be using their PCs as data loggers, controllers or as web servers. ln these cases it is important that the machine is kept powered up for as great a fraction of the time as possible, even if there has been a power cut or if the power button is inadvertently pressed by another member of the household. Todays operating systems offer a range of automation options and it is perfectly possible to arrange things so that the computer starts itself up automatically.

Always on for PCs Circuit diagram :

The always oncircuit shown here automatically restarts an ATX PC in the above situations. There are just two components: a Schottky diode connecting the power but-ton pin on the motherboard to the +5 V line on the power supply, and a capacitor from the power button pin to ground. The capacitor is a 68 pF tantalum type rated at 6.3 V, and the diode is a type SB 120, rated at 20 V and 1 A. The total component cost is in the sub-one-beer range!

The most convenient arrangement is to mount the circuit directly on a 4-way Molex disk drive power plug, insulating the capacitor and diode using heatshrink tubing. The assembly can then be plugged into a spare socket on the power supply.

The operation of the circuit is straightforward. When the +5 V supply fails (i.e., when the computer is turned off), the power button pin on the motherboard is pulled low via the Schottky diode. This instructs the motherboard to power up again. As long as the +5 V supply is present, the diode blocks and the power button pin remains at high impedance, floating typically at around 3.3 V. The capacitor serves to filter out spikes and brief dropouts. ln its simpler version the circuit replaces the power button on the case, and the computer can now only be switched on and off at the mains.

The author has tested the circuit on modern SuperMicro X8SAX and XSDTH-6F mother-boards as well as on an olderTyan Tiger MPX. He found that the capacitor value should be reduced in some cases: the SuperMicro motherboards have a high internal pull-up resistance which only charges the capacitor rather slowly.

Note that some PC keyboards have a Sleep button which puts the computer into a low-power mode. ln this case the circuit will not work, and you should either use a keyboard without such a button or disable sleep modes from within the operating system. ln its more advanced version the existing power button is retained in parallel with the circuit (see circuit diagram). The power button then causes a graceful shutdown whereby the operating system can bring the computer to a halt in an orderly manner.

Source : http://www.ecircuitslab.com/2012/06/always-on-for-pcs-circuit.html

Saturday, October 4, 2014

IC 555 based on water Activated Alarm

This water activated alarm circuit uses a NE555 timer wired as an astable oscillator and powered by the emitter current of transistor BC109C. In dry conditions, the transistor having no bias current and be completely off. As the probe gets wet, a small current flowing between the base and the emitter and the transistor turns on. A higher current flow in the collector circuit allows the IC NE555 osillator sound.

Probe / contacts may use a nonreactive metal. Contacts gold plated or silver age relay can be used, however, a cheaper alternative is the thread of alternate strips of copper a piece of veroboard. These will eventually oxidize over but as very little current flowing in the base circuit, the higher the impedance caused by oxidation is not important. No base resistor is necessary as the transistor is in emitter follower, current limit is the impedance at the emitter (the oscillator circuit)

Tuesday, September 16, 2014

– Voltage On Bargraph Display

The LM3914 is a truly versatile component. Besides LEDs, only a few other components are needed to make the ‘bidirectional’ bargraph voltmeter shown here. The circuit is similar to a conventional bar display, but it offers a possibility to change the direction in which the LEDs are switched on. This may be useful, for example, when positive and negative voltages are measured. For a positive input voltage, the LEDs are switched on in the usual manner, that is, from D3 to D12, while for negative voltages, the LEDs are switched on in the opposite direction, from D12 to D3. Obviously, the negative voltage must be ‘rectified’, i.e. inverted, before the measurement.

A suitable circuit for this purpose is presented in the article ‘Absolute-value meter with polarity detector’ elsewhere in this website. A set of transistor switches (MOSFETs) controls the direction in which the LEDs light. When the control voltage is high (+6V, according to the schematics, but any voltage that is at least 3V higher than reference voltage will do), T1 and T4 are switched on, while the other two MOSFETs are off. In this way, the LM3194 is configured in the usual manner with the top end of the resistor network connected to the internal voltage reference and the low end connected to ground.

+/–

As the input voltage rises, the comparators inside the LM3914 will cause the indicator LEDs to be switched on one by one, starting with D3. When the control voltage is lower than about –3V, T2 and T3 are switched on while T1 and T4 are off. Consequently, the ends of the resistor network are connected the other way around: the top end goes to ground and the low end, to the reference voltage. The first LED to be switched on will then be D12; i.e., the LEDs that forms the bargraph display light in the opposite direction. Although not documented by the manufacturer of the LM3914, this option works well, but only in bar mode (in dot mode, internal logic disables any lower-numbered LEDs when a higher-numbered LED s on, which obviously conflicts with our purposes).

To achieve good symmetry, an adjustable resistor is added to the voltage divider in the LM3914. Using a DVM, adjust the preset until the voltage across P1+R4 equals 1/11th part of Urefout. Sensitivity is determined with the ratio of resistors R5 and P2. If, for example, the reference voltage is set to 2.2 V by means of P2, there will be a voltage drop of 200 mV per resistor in the ladder network (including R4-P1). So, the first LED will switch on when the input voltage exceeds 200 mV, the second, at 400 mV, and so on, and the whole display will be on at 2 V. The circuit draws about 100 mA when all LEDs are switched on.

Saturday, September 13, 2014

50W Power Amplifier circuit based on STK 1050

Here is one of the schema diagram of a power amplifier with the STK1050 single power chip which is supported by several components that make a better sound output. This amplifier is a single output amplifier, so if you want a stereo amplifier, then you must make a similar schema.

50W

STK-1050 Features:
STK1050 has some features that make it superior and good for your audio amplifier.

Does not require externally connected emitter resistors.
Values of emitter resistors have carefully been reviewed to provide superior characteristics.

Better supply voltage utilization permits designing power supply voltage that are about 0.7V (for RL=4ohms) lower than those required for previous DPP models.
Maximum allowable power consumption for each resistor is 5W or higher, permitting accomodation for all loads.
Peak allowable current is 18A or more, providing an ample margin even for peak currents under when short schemaed or similar emergencies.
In particular, maximum output 4 ohms have been enormously improved.

Use of emitter resistors facilitates meeting different safety standards and designing PCBs
Mutual interferences in the high-frequency range caused by layout of externally connected emitter resistors no longer exist. This facilitates lower distortion factors.
Pins are used for emitter resistor output terminals that were not conected in previous DPPs. All other terminals remain uncharged; there is no need for major schema board changes.

Download STK-1050 datasheet

Friday, September 12, 2014

Electronic Transistor Turns Op Amp On or Off Wiring diagram Schematic

Build a Electronic Transistor Turns Op Amp On or Off Circuit Diagram. In this schema When transistor Q1 is switched off, the schema behaves as a voltage follower. By applying a positive voltage to the emitter of Q1 via a 10 KOhmhm resistor, the transistor is made to turn on and go into saturation. Thus, the lower end of R4 is connected to ground.

Electronic Transistor Turns Op Amp On or Off Circuit Diagram

The schema has not changed into that of a differential amplifier, except that the voltage difference is always 0 V. As long as the resistor ratios in the two branches around the op amp are in the same ratio, the output should be zero. A 47-KOhm resistor is used to null out any ratio errors so that the off attenuation is more than 60 dB. The high common-mode rejection ratio of a 741 enables this large attenuation to be obtained.

Wednesday, September 10, 2014

Signal strength indicator on the 64 LEDs

I present to you a simple project indicator audio signal, a distinctive feature of this project from others is that in the scheme for each channel I primel 32 LEDs to get the long line. At the heart device - AVR microcontroller Atmel ATmega8535, ULN2803 - 8-channel key Darlington, moreover, operational amplifiers, his appointment think its also clear. Sensitivity indicator is adjusted by resistors R32 and R33, for each channel separately. This project is my thesis work I did a couple of years ago, when the scheme came across sharilsya in folders on your PC, and decided to send to the site.

The scheme is quite large, reduce LED designation did not, the scheme can be found below:

As for the LEDs, it is convenient to replace the special LED bars, besides, they will look better.

The entire device is going on a breadboard, PCB did not draw who liked the project can draw the circuit board and send it to the forum. All radio components in the circuit can be replaced by a similar, resistor and capacitor can be placed close to par. The transistors may be replaced by any other similar. Crystal oscillator can be put on 14-16 MHz, is not critical. Photos of the device below:

When programming the microcontroller does not need to put fuse bits, ie we select the desired controller in the program, open firmware and click flash. If the device is assembled correctly, the circuit work immediately.

Original article sourse cxem.net

Saturday, August 23, 2014

Solving the problem on tv tuner

Tv tuner serves as the catcher signals from the antenna. Damage tuner, among others:

1. Image does not exist and there is no sound, raster speckled thick.

2. No picture no sound, or otherwise.

3. Channel switching the channel itself.

4. Image blocking white or blue.

How to check the tuner and the IF is to remove the tuner from the PCB and connected by cable to the IF path, BM and Ground, then prepared using the pin on the tuner. Then the television was turned on, the antenna is connected to the antenna socket, and RV or potensio rotated slowly to choose the television channel when the tuner is in normal condition, the signal from the antenna to be acceptable, the picture and sound, and the channels do not move themselves. To damage its own channel switch and checked the normal manner stated above, the location of damage on the section of the program.

Saturday, August 16, 2014

Electronic Push on Push off Switch Wiring diagram Schematic

This is a simple Electronic Push-on Push-off Switch Circuit Diagram. Transistors Ql and Q2 make up the flip-flop while Q3 drives a reed relay. When power is first applied to the schema, Ql and Q3 are conducting and Q2 is cut off. Momentarily closing SI causes the flip-flop to switch statesâ€”Ql cuts off and Q2 conducts. When Q2 is conducting, its collector drops to around 0.6 volt.

Electronic Push-on Push-off Switch Circuit Diagram

That prevents base current from flowing into Q3 so it is cut off, de-energizing relay Kl. The flip-flop changes state every time SI is pressed. Capacitors Cl and C2 ensure that Ql is always the transistor that turns on when power is first applied to the schema. When power is first applied to the basic flip-flop, the initial status is randomâ€”Ql and Q2 both try to conduct and, usually, the transistor with the higher gain will take control, reaching full conduction and cutting off the other one.

However, differences in the values of the collector and coupling resistors will also influence the initial state at power-on. With C2 in the schema, it and R4 form an R-C network that slightly delays the rise in Q2s base voltage. That gives Ql sufficient time to reach saturation and thus take control.