Simple Digital Switching System

This circuit can control any one out of 16 devices with the help of two push-to-on switches. An up/down counter acts as a master-controller for the system. A visual indication in the form of LEDs is also available.  IC1 (74LS193) is a presettable up/ down counter. IC2 and IC3 (74LS154) (1of 16 decoder/demultiplexer) perform different functions, i.e. IC2 is used to indicate the channel number while IC3 switches on the selected channel.

Digital Switching System Circuit Diagram :

Before using the circuit, press switch S1 to reset the circuit. Now the circuit is ready to receive the input clock. By pressing pressing switch S2 once, the counter advances by one count. Thus, each pressing of switch S2 enables the counter to advance by one count. Likewise, by pressing switch S3 the counter counts downwards.

The counter provides BCD output. This BCD output is used as address input for IC2 and IC3 to switch one (desired channel) out of sixteen channels by turning on the appropriate triac and the corresponding LED to indicate the selected channel.  The outputs of IC3 are passed through inverter gates (IC4 through IC6) because IC3 provides negative going pulses while for driving the triacs we need positive-going pulses. The high output of inverter gates turn on the npn transistors to drive the triacs. Diodes connected in series with triac gates serve to provide unidirectional current for the gate-drive.

Sorce : www.ecircuitslab.com/2012/08/digital-switching-system.html

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Fox Hunt Transmitter

This 2 meter 144 MHz fox hunt transmitter is used in amateur competitions where a hidden transmitter is to be “hunted” using mostly home brewed receivers and antennas. The foxhunt electronic circuit is the transmitter. It radiates a high quality signal without unwanted harmonics. Transistor T1 and the crystal together make the oscillator that generates a 36MHz signal.

The unwanted 12MHz basic frequency of the oscillator is suppressed by the filter circuit made of L1, C3, C2. The L2/C4 circuit is set to the fourth harmonic or 144 MHz. The signal goes to the dual-gate-FET driver stage before finally radiating through the transmitting antenna. The output power is from 10…40mW. The radiated signal is also modulated by the gate circuit made of U1, U2, U3, U4. Gate U1 is a low frequency oscillator which generates a signal from 0.1 to 0.5Hz. This signal modulates the transmitter through the transistor T3.

Fox Hunt Transmitter Circuit diagram

If the U1 output is “0″, transistor T3 is off and the transmitter is also off. On the other hand, if the U1 output is “1″, transistor T3 is on and the transmitter is on. During the “1″ period, gate U2 generates a square wave signal with a frequency form 0.1 to 1Hz. Gate U3 works as an inverter only. It determines whether gate U4 generates a 1KHz signal or not. A periodic burst signal is now present at the gate FET T2 to modulate the transmitter used at foxhunt.

Calibration of the foxhunt transmitter: Adjust the three trimmer capacitors to produse a maximum signal amplitude at the output.
Coil data:
L1 = 470 nH
L2 is made of 5 windings of 0.8mm copper wire, 8 mm winding diameter. It is tapped at the first winding from the ground.
L3 is made of 0.8mm copper wire, 8mm winding diameter, 3 windings at the FET side and 2 windings at the antenna side. Adjust the coupling between the two windings sides to get a maximum signal output amplitude.
The circuit can be powered with a 9 volt battery. It consumes around 20mA only.

Fox Hunt Transmitter Active Components.

T1 = 2SA256
T2 = 3N205
U1, U2, U3, U4 = IC1 = 4093

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the layout of the electricity line around cell phone jammers should be done

And some revise of the layout of the electricity line around  cell phone jammers should be done.
And mobile, China Unicom, not limited to the scope of telecommunications triple-play cell phone number to send, according to the specific needs of custom personalized service. Students as a distinct group, have higher education, higher information needs with the progress, contact television and other media opportunities, the phone reports that the new target audience. Campus mobile newspaper reading population is more focused and precise, and naturally become a new choice in the promotion of business products. Campus phone reported. Campus mobile newspaper "News" is the fundamental content. Planning Students mobile newspaper content loved by readers, of course, we must first understand the interest of the target audience of university students, according to their characteristics, needs.  Industrial environment: As the sponsor reasonable ease the demand for advertising, legal and mobile advertising services, so in fact played a large role in governance spam messages, thereby purifying the industrial environment, the industrial chain win. Status and Prospects of the development of mobile media. As information technology continues to progress, the original mobile phone as an interpersonal exchange of information intermediaries.
Rather to ensure that each piece of information, "Jane and deep." To do Jane and deep "will be a higher demand for editing, you need enough news sensitivity. Such as to make the correct interpretation of the country, the government introduced the policy of involving university students to study or work, and make predictable judgments, and even make incisive reviews, make the appropriate adjustments to help and facilitate college students to use the relevant policies give practical advice. Recommendations for mobile newspaper audience attention of contention. According to the spread scientist Melvin De Fule theory, when major changes occur, the audience will generate an exception to the media rely on. Which media can be timely and adequate to provide information to who he would rely on.  However, todays mobile newspaper is considered to be a subsidiary of the print media, the contents of the value of the performance of the force and the media not been fully recognized and mining. Information personalization. First of all must be aware, mobile newspaper should not just newspapers optional supplement. The mobile newspapers content to get out of the shadow of the newspaper, to form their own style and play their own unique advantages, mining the content of expression, and expansion of channel function.

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Rear Light After Glow For Bicycles

This article is of interest only to readers whose bicycle lights are powered by a dynamo. The laws on bicycle lights in the United Kingdom are stricter than in other countries and a dynamo is, therefore, a rarity in this country. From the point of view of traffic safety it is advisable (in UK obligatory) for cyclists to have the rear lamp of their bicycle to light even when they are at standstill.

In principle, it is not very difficult to modify the existing rear light with afterglow: all this needs is a large enough energy reservoir. Since the after-glow is required for short periods of time only, a battery is not required: a large value capacitor, say, 1 F, is quite sufficient.As the diagram shows, in the present circuit, the normal rear light bulb is replaced by two series-connected bright LEDs, D2 and D3. These are clearly visible with a current of only 6 mA (compared with 50 mA of the bulb).

The current is set with series resistor R1. The LEDs are shunted by the 1 F capacitor, C1. Since the working voltage of this component is only 5.5 V, it is, in spite of its high value, physically small. An effective regulator is needed to limit the dynamo voltage adequately. Normal regulators cannot be used here, since they do not work at low voltages. Moreover, such a device would discharge the capacitor when the cycle is at standstill.

Circuit diagram :

Rear Light After Glow Circuit Diagram

Fortunately, there is a low-drop type that meets the present requirements nicely: the Type LP2950CZ5.0. Of course, the dynamo output voltage needs to be rectified before it can be applied to the regulator. In the present circuit, this is effected by half-wave rectifier D1 and buffer capacitor C2. Diode D1 is a Schottky type to keep any losses low – important for this application, because the ground connection via the bicycle frame usually causes some losses as well. The value of buffer capacitor has been chosen well above requirements to ensure that C1 is charged during the negative half cycles of the dynamo voltage.

Source : www.extremecircuits.net

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Flip Flop Timer Using 4017

This circuit shows how a 4017 CMOS decade counter can be used to build a timer circuit. Push-button S1 will discharge capacitor C1 through resistor R2. When S1 is released, C1 will charge up through R1 causing a rising edge at the clock input of IC1. This causes the output Q1 to go high (to the supply voltage). Current will flow through R4 and LED D2 will light. At the same time C2 will begin charging through preset P1 and R6. When the voltage on C2 reaches approximately half the supply voltage it will reset IC1. Q1 will go low, the LED will go off and C2 will discharge through D1 and R3. The circuit will now remain stable in this reset condition until S1 is pressed again. Preset P1 allows the ON time of the circuit to be adjusted between 5 seconds and 7 minutes.

The current consumption of this circuit in its reset state is only a few micro-amps, rising to approximately 8mA mainly due to the LED current, when S1 is pressed. When power is applied to the circuit IC1, can be in an indeterminate state and the LED may be on. Pressing S1 until the LED goes off clears this condition. Alternatively C2 may be connected to the supply rail (as shown dotted in the diagram) this will ensure that IC1 will always power up in a reset state. A disadvantage of this configuration is that any noise on the supply rail will be coupled through to the reset pin of IC1 and may affect the timing period.

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Rolling Shutter Motor Control

An electrically operated rolling shutter usually has a standard control panel with a three-position switch: up, down and stop. If you would like to automate the opening and closing with a time controlled switch, a few additional wires will have to be connected. Typically, the controls are implemented as indicated in the schematic ‘Normal Situation’. If this is indeed the case, then you can see in ‘New Situation’ how the shutter can be automated with a timer. There is only one method to determine the actual schematic of your control circuit, and that is to open the control box and using an ohmmeter, pencil and paper to check out and draw the circuit. Make sure you turn the power off first though! Connect a 230-V relay (with both the contacts and the coil rated 230 VAC) to the timer.

The changeover switch between automatic and manual control needs to be rated 230 VAC as well and may not be a hazard for the user. The relay and switch are preferably fitted in a plastic mains adapter enclosure with built-in plug, which is plugged into the timer. It is a good idea to check first if this will actually fit. Because of the manual/automatic-switch, the operation is completely fail-safe and misunderstandings are out of the question. The switch prevents the issue of conflicting commands (with disastrous consequences) when, for example, the shutter is being automatically raised and manually lowered at the same time.

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12V Halogen Dimmer

I use a 12V 20W halogen lamp (MR16) and a 4.2Ah SLA battery for my bike light system. The battery has only limited life at this power rating, so I designed this cheap light dimmer to reduce the battery drain and allow for longer rides at night. Based on a simple 555 timer circuit and Mosfet switch Q1, it works by pulse-width modulating the 12V supply to the lamp. The 555 (IC1) is wired as a free-running oscillator, with two different mark/space ratios selectable via a 2-pole, 5-position rotary switch (S1). The third switch position bypasses the electronic circuitry and connects the lamp directly to battery negative. This gives three power levels of about 7W, 13W and 20W. A logic-level IRL530N Mosfet with a drain-source "on" resistance of only 0.1Ω ensures low losses and eliminates the need for a heatsink. An STP30NE06L Mosfet (Jaycar Cat. ZT-2271) would also be suitable.

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