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Thursday, August 8, 2013

Simple Automatic Switch For Audio Power Amplifier

Circuit of an automatic switch for audio power amplifier stage is presented here. The circuit uses stereo preamplifier output to detect the presence of audio to switch the audio power amplifier on only when audio is present. The circuit thus helps curtail power wastage. IC1 is used as an inverting adder. The input signals from left and right channels are combined to form a common signal for IC2, which is used as an open loop comparator. IC3 (NE556) is a dual timer. Its second section, i.e., IC3(b), is configured as monostable multivibrator. Output of IC3(b) is used to switch the power amplifier on or off through a Darlington pair formed by transistors T1 and T2. IC3(a) is used to trigger the monostable multivibrator whenever an input signal is sensed.

Circuit diagram:

Automatic Switch For Audio Power Amplifier Circuit Diagram

Under ‘no signal’ condition, pin 3 of IC2 is negative with respect to its pin 2. Hence the output of IC2 is low and as a result output of IC3(a) is high. Since there is no trigger at pin 8 of IC3(b), the output of IC3(b) will be low and the amplifier will be off. When an input singal is applied to IC1, IC2 converts the inverted sum of the input signals into a rectangular waveform by comparing it with a constant voltage which can be controlled by varying potentiometer VR1. When the output of IC2 is high, output pin 5 of IC3 goes low, thus triggering the monostable multivibrator. As soon as the audio input to IC1 stops, pin 5 of IC3 goes high and pin 1 of IC3 discharges through capacitor C3, thus resetting the monostable multivibrator.

Hence, as long as input signals are applied, the amplifier remains ‘on.’ When the input signals are removed, i.e., when signal level is zero, the amplifier switches off after the mono flip-flop delay period determined by the values of resistor R8 and capacitor C3. If no input signals are sensed within this time, the amplifier turns off—else it remains on. Power supply for the circuit can be obtained from the power supply of the amplifier. Hence, the circuit can be permanently fitted in the amplifier box itself. The main switch of the amplifier should be always kept on. Resistors R1 and R2 are used to divide single voltage supply into two equal parts.

Capacitors C1 and C2 are used as regulators and also as an AC bypass for input signals. Diode D1 is used so that loading fluctuations in power amplifier do not affect circuit regulation. Transisitor T2 acts as a high voltage switch which may be replaced by any other high voltage switching transistor satisfying amplifier current requirements. Value of resistor R10 should be modified for large current requirement. The LED glows when the amplifier is on. The circuit is very useful and relieves one from putting the amplifier on and off every time one plays a cassette or radio etc.

http://streampowers.blogspot.com/2012/06/simple-automatic-switch-for-audio-power_11.html

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Friday, April 12, 2013

Automatic Curtain Opener

This circuit can be used with a timer clock to open and shut curtains or (vertical) Venetian blinds. The curtain or blind is pushed by using an electrical motor with a discount gearbox suited to the keep watch over mechanism of the curtain or blind. This circuit is good for giving your home an occupied look when you are away on vacation or for any different reason. In the author’s house, this association has provided a few 12 monthss of trouble-free carrier on quite a few home windows fitted with Venetian blinds.

The unique design was once a easy relay circuit with pushbuttons for opening and shutting and reed switches acting as restrict switches. The mechanical force is equipped by using a small DC motor with a reduction gearbox and pulley (all from Conrad Electronics). It used to be later modified to work robotically with a timer clock. The timer operates a small 230-VAC (or 120-VAC) relay with a changeover contact. Thanks to the two timers, the motor stops after just a few 2nds if probably the most reed switches is overlooked as a consequence of a mechanical defect.

Circuit diagram :
$\"Automatic-Curtain$

Automatic Curtain Opener Circuit Diagram

The circuit works as follows (see Figure 1). In the quiescent state, relays RE1–RE3 are de-energised and the motor is ceaseped. Open the blind:

When the timer clock applies power to the 230-V (120-V) relay RE3, the voltage on the junction of C1 and R1 goes high. IC1 (a 555) then receives a set off pulse on pin 2, which lead tos its output (pin 3) to go High and energise RE1, which in turn result ins the motor to begin running. When the magnet reaches reed swap S1 (‘Open’), the 555 is reset. If the reed switch does no longer function for some purpose, the relay is de-energised anyways when the monostable times out (time extend = 1.1 RC; roughly 5 seconds). Close the blind:

The timer clock cast offs power from RE3, which causes a trigger pulse to be utilized to the opposite 555 timer (IC2) via R5 and C4. Now the motor starts operating within the other direction. The rest of the operation is similar as described above for opening the blind. Diodes D2 and D5 stop the outputs of the 555 ICs from being pulled bad when the relay is de-energised, which could differentwise result in the timer ICs to malfunction.

All elements of the mechanical power come from Conrad Electronics [2]: a motor with a reduction gearbox (type RB32, order quantity 221936) and a pulley (V-belt pulley, order number 238341) on the output shaft. An O-ring is suited to the pulley to provide sufficient friction with the force chain of the Venetian blind. The magnet for actuating the reed swapes is a rod magnet with a hole within the middle (order number 503659), and the chain of the Venetian blind is fed thru this hole.

Author : Ton Smits - Copyright : Elekto

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LM317 Automatic Low Cost Emergency Light

Here is an emergency lighting based on white LEDs offer the following advantages:

1. It is very bright thanks to the use of white LEDs.

2. The light turns on automatically when the mains fails and shuts down when power resumes.

3. It has its own office. When the battery is fully charged, the charging stops.

The circuit consists of two parts: the charger from the socket and the power LED part driver.The Charger is built around the 3-terminal adjustable regulator (IC1) LM317, while the LED driver is built on part of the transistor BD140 (T2). In the power charger power transformer in the AC input is a step down to give a 9V 500mA bridge rectifier consisting of diodes (IN4007x4). Filter capacitor (25v/1000uf) to eliminate the ripples. Unregulated DC power is fed to IC1 pin 3 and provides a charging current through the diode IN4007 (D5) and limiting resistance (16ohm) R16. By providing pre-k 2.2 (VR1), the output voltage can be adjusted to provide the required charging current. When the battery may require a 6.8V, and the barrier makes the charging current regulator (IC1) to find a path through the transistor BC547 (T1) to ground and stops charging. LED driver section is used a total of twelve 10 mm white LEDs.

Circuit diagram :

LOW-COST-AUTOMATIC-EMERGENCY-LIGHT-e1297471252686 Automatic Low Cost Emergency Light LM317 Circuit diagram

All LEDs are connected in parallel with the resistance of 100 ohms in series with each other. junction common anode for all twelve LED is connected to the collector of PNP transistor T2 and the emission level of the transistor T2 is directly related to the positive terminal of 6V battery. Unregulated DC voltage produced by the cathode junction of Bridge (diodes), is fed to create a transistor T2 through a resistor of 1k. When the voltage is available, the fund is still high transistor T2 and T2 does not happen. The lights are off. On the other hand, if the power does not, the transistor T2 will be a small fund and it does. This causes all the LEDs (LED1 through LED12) is lit. Network, as it is available, download and keep the lights off the battery as an indicator of transistor T2 is cut-off. During the blackout, the workload is steady and makes the battery will light up.

Assemble the circuit on a general purpose PCB and enclose in a cabinet with enough space for the battery and switches. Mount the LED in the housing to illuminate the room. A hole in the box must be drilled to connect the 230V AC input to the transformer primary. I tested the circuit with twelve white 10 mm LEDs.You can use several diodes, provided that the total energy consumption does not exceed 1.5. Driver transistor T2 can provide up to 1.5 In accordance with a proper heat sink.

Source : freecircuit.net

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