Showing posts with label on. Show all posts
Showing posts with label on. Show all posts
Tuesday, October 8, 2013
AF Amplifier With Digital Volume Control Based On TDA8551
The Philips Semiconductors TDA8551 is a small audio amplifier with an integrated volume control. When operated from +5 V, it delivers a nominal output power of more than one watt into 8 ohms. It can also be used over a supply voltage range of +2.7 to +5.5 V, with correspondingly reduced output power. The output volume can be adjusted from –60 dB to +20 dB in 64 steps, using a set of up and down push-buttons. The shared UP/DOWN input for the up and down switches has three states. If it is ‘floating’, which means that both of the switches are open, the volume remains unchanged. A pulse to earth decreases the volume by 1.25 dB, while a positive pulse increases the volume by 1.25 dB.
When the power is switched on, the internal counter takes on the –20 dB setting. An additional input (MODE) allows the amplifier to be switched from the operating state to the mute or standby state. If this input is held at the earth level, the amplifier is operational. If +5 V is applied to this pin, the TDA8551 enters the Standby mode, in which the current consumption drops from the typical operational level of 6mA to less than 10µA. Finally, the MODE input can be used as a mute input by applying a voltage of 1 t0 3.6 V to this input. This voltage can be provided by a connection to the SCR pin, which lies at half of the operating voltage and to which a filter capacitor is connected.
The loudspeaker is connected in a floating configuration between the two outputs of the bridge amplifier in the TDA8551. This provides the desired output power level, in spite of the low supply voltage. For headphone applications, which do not need as much output power, you can connect the headphone between earth and one of the outputs, via an electrolytic coupling capacitor. You can make a stereo headphone amplifier in this way, using two TDS8551 ICs. The TDA8551 is housed in a DIP8 package. The SMD version is the TDA8551T, in an SO8 package.
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When the power is switched on, the internal counter takes on the –20 dB setting. An additional input (MODE) allows the amplifier to be switched from the operating state to the mute or standby state. If this input is held at the earth level, the amplifier is operational. If +5 V is applied to this pin, the TDA8551 enters the Standby mode, in which the current consumption drops from the typical operational level of 6mA to less than 10µA. Finally, the MODE input can be used as a mute input by applying a voltage of 1 t0 3.6 V to this input. This voltage can be provided by a connection to the SCR pin, which lies at half of the operating voltage and to which a filter capacitor is connected.
The loudspeaker is connected in a floating configuration between the two outputs of the bridge amplifier in the TDA8551. This provides the desired output power level, in spite of the low supply voltage. For headphone applications, which do not need as much output power, you can connect the headphone between earth and one of the outputs, via an electrolytic coupling capacitor. You can make a stereo headphone amplifier in this way, using two TDS8551 ICs. The TDA8551 is housed in a DIP8 package. The SMD version is the TDA8551T, in an SO8 package.
Friday, April 12, 2013
Wireless On Off Switch
Normally home appliances are controlled by means of switches, sensors, etc. However, physical contact with switches may be dangerous if there is any shorting. The circuit described here requires no physical contact for operating the appliance. You just need to move your hand between the infrared LED (D2) and the phototransistor (Q1).
Wireless On-Off Switch Circuit diagram :
The infrared rays transmitted by D2 is detected by the phototransistor to activate the hidden lock, flush system, hand dryer or else. This circuit is very stable and sensitive compared to other AC appliance control circuits. It is simple, compact and cheap. Current consumption is low in milliamperes. The circuit is built around an IC CA3140, D2, phototransistor and other discrete components.
Parts:
R1 = 470R
R2 = 100K
R3 = 3.3K
R4 = 10K
D1 = 1N4007
D2 = IR LED
Q1 = L14F1
RL = 5Vdc Relay
IC = CA3140
Q2 = BC548
R2 = 100K
R3 = 3.3K
R4 = 10K
D1 = 1N4007
D2 = IR LED
Q1 = L14F1
RL = 5Vdc Relay
IC = CA3140
Q2 = BC548
Circuit Operation:
When regulated 5V is connected to the circuit, D2 emits infrared rays, which are received by phototransistor Q1 if it is properly aligned. The collector of Q1 is connected to non-inverting pin 3 of IC1. Inverting pin 2 of IC1 is connected to voltage-divider preset R4. Using preset R4 you can vary the reference voltage at pin 2, which also affects sensitivity of the phototransistor. Op-amp IC1 amplifies the signal received from the phototransistor. Resistor R3 controls the base current of transistor BC548 (Q2). The high output of IC1 at pin 6 drives transistor Q2 to energies relay RL1 and switch on the appliance, say, hand dryer, through the relay contacts.
The working of the circuit is simple. In order to switch on the appliance, you simply interrupt the infrared rays falling on the phototransistor through your hand. During the interruption, the appliance remains on through the relay. When you remove your hand from the infrared beam, the appliance turns off through the relay. Assemble the circuit on any general-purpose PCB. Identify the resistors through colour coding or using the multimeter. Check the polarity and pin configuration of the IC and mount it using base. After soldering the circuit, connect +5V supply to the circuit.
Source : www.ecircuitslab.com/2011/05/wireless-on-off-switch.html
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
Tuesday, April 9, 2013
Process formation of RGB signal on TV
Basically the UOC is equipped with RGB or YUV input from external, so it is possible to use the DVD input. Selection of these inputs can be done internally within the IC. But in the G7 and G7A chassis input YUV signal is not used, so in the ground.
RGB signal processing flow is described according to the image below :
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| Diagram of the formation RGB signal |
1. Signal Yint, uint, and Vint is derived from a series of color decoder and Y / C switch is fed into a series of YUV selector 1.
2. From YUV selector, sub-carrier signal color (U and V) is inserted into the chain matrix. In this matrix series component sub-carrier signal BY of the color (U signal) and BY component of sub-carrier signal color (V signal) in separate. Here the color difference signal in the form of the color sub carrier. GY signal generated by a combination of color difference signals RY and BY.
3. From YUV selector, luminan signal is passed to a series of black stretch. The working principle is to sharpen the series of black stretch black levels. Gray color in a certain percentage in drag to a black color so the color is sharper.
4. Three color difference signals (RY), (BY) (GY) and luminan signal (Y) are mixed and processed in RGB adder circuit to produce three primary colors red, green and blue (RGB).
5. RGBOSD formed in the UOC IC is used to display the OSD text. The selection and arrangement RGBOSD kontrast between RGB and composite signals is done by way of a switch by the internal microprocessor.
6. Three output video signal (RGB signal) is assumed as the current that flows to the CRT cathode. Drive level coming into the cathode tube is always diadjust by CCC loop (Continues Cathode Calibration) and feedback currents in pass to Black Current Input pin 50.
7. CCC loop works as a stabilizer against the black level and drive the cathode in a loop (continuous) to the RGB signal in order to obtain the proper offset and gain.
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| CCC Loop Application |
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