Pump Controller For Solar Hot Water System

This circuit optimises the operation of a solar hot water system. When the water in the solar collector is hotter than the storage tank, the pump runs. The circuit comprises two LM335Z temperature sensors, a comparator and Mosfet. Sensor 1 connects to the solar collector panel while Sensor 2 connects to the hot water panel. Each sensor includes a trimpot to allow adjustment of the output level. In practice, VR1 and VR2 are adjusted so that both Sensor 1 and Sensor 2 have the same output voltage when they are at the same temperature. The Sensor outputs are monitored using comparator IC1.

When Sensor 1 produces a higher voltage than Sensor 2, which means that sensor 1 is at a higher temperature, pin 1 of IC1 goes high and drives the gate of Mosfet Q1. This in turn drives the pump motor. IC1 includes hysteresis so that the output does not oscillate when both sensors are producing a similar voltage. Hysteresis comprises the 1MO feedback resistor between output pin 1 and non-inverting input pin 3 and the input 1kO resistor. This provides a nominal 12mV hysteresis so that voltage at Sensor 1 or Sensor 2 must differ by 12mV for changes in the comparator output to occur.

Circuit diagram:

Since the outputs of Sensor 1 and Sensor 2 change by about 10mV/°C, we could say that there is a degree of hysteresis in the comparator. Note that IC1 is a dual comparator with the second unit unused. Its inputs are tied to ground and pin 2 of IC1 respectively. This sets the pin 7 output high. Since the output is an open collector, it will be at a high impedance. Mosfet Q1 is rated at 60A and 60V and is suitable for driving inductive loads due to its avalanche suppression capability. This clamps any inductively induced voltages exceeding the voltage rating of the Mosfet.

The sensors are adjusted initially with both measuring the same temperature. This can be done at room temperature; adjust the trimpots so that the voltage between ground and the positive terminal reads the same for both sensors. If you wish, the sensors can be set to 10mV/°C change with the output referred to the Kelvin scale which is 273K at 0°C. So at 25°C, the sensor output should be set to (273 + 25 = 298) x 10mV or 2.98V.Note:The sensors will produce incorrect outputs if their leads are exposed to moisture and they should be protected with some neutral cure silicone sealant. The sensors can be mounted by clamping them directly to the outside surface of the solar collector and on an uninsulated section of the storage tank. The thermostat housing is usually a good position on the storage tank.

Author: John Clarke - Copyright: Silicon Chip Electronics

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Preamp Stage For Ceramic Phono Cartridge Or Violin Pickups

While we have published a number of variations on a standard RIAA preamplifier for magnetic phono cartridges, we have not published a preamp stage for ceramic phono cartridges. Typically, these were supplied as turnover cartridges in record changers but there were higher quality versions such as the Decca Deram. These phono cartridges are piezoelectric devices which require a very high input impedance. Similarly, violin pick-ups made by Fishman, Barcus Berry and others are piezo devices. These two circuits have been requested for a violin pickup but could equally well suit a ceramic or crystal pickup. The op amp circuit uses a TL071 connected as a voltage-follower. It can run from a battery supply of ±9V.

Circuit diagram:

The alternative transistor circuit uses a BC549 connected as an emitter-follower but with bootstrapping of the input bias network to provide a high input impedance. Both circuits have input coupling capacitors but since the transducers are capacitive (ie, piezo) they could possibly be omitted. Both circuits will probably need to be followed by further gain, depending on the output level. For a violin pickup, a parametric equaliser is also recommended, and for this we would suggest the 3-band parametric equaliser published in the July 1996 issue of SILICON CHIP. With a slight change to the feedback of the first op amp in this circuit, the extra gain required could also be provided.

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Simplest Single Phase Preventor Circuit for Three Phase Motor Potection

 For a 3-phase induction motor,Lit is necessary that all the three phases of supply are present while it is on load.
When any one of the fuses goes out, or a phase is missing, the motor will continue to run with two phases only, but it will start drawing a huge current for the same load.

This high current may ruin the motor, unless switched off immediately. A single phase preventor circuit avoids such a mishap. With this circuit the motor will not run, unless all the three phases are present. In a 3-phase supply, the voltages are 120 degrees apart from each other. Thus the addition of three phases gives zero voltage. lf any one of the phase goes, voltage present at the summing point equals half the line voltage. ‘ In this circuit, the three phases (R, Y, B) are connected to line neutral, which in turn is connected to the ground of the   circuit.

When all three phases are present, voltage at point D is zero. So potential at pin 3 of 1C 741 is also zero, but voltage at pin 2 is nearly 4V. Here 741 is used as a comparator and the voltage at pin 6 is zero. Hence the relay cannot operate. When a phase goes out, voltage at point D goes up to about halt the line voltage. This voltage is divided by 150k and 50k resistors. The voltage at pin 3 is about 8V when 50k potentiometer is properly adjusted. The voltage at pin 6 is about 12V. This base voltage can drive the relay into operating condition. So, the relay would operate when any of the phases goes out.  This relay, when used in the control circuit of the 3-phase motor, or with a circuit breaker, would switch the power oft on operation.

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Brightness Control for 1 5v bulbs

Lots of people ask about low voltage brightness control diagram so i believe this can be very useful schema for you.I suppose you can use this for various purposes.So try this schema...







Parts:

Q1 BD681 100V 4A NPN Darlington Transistor

P1 470K Linear Potentiometer

C1 22nF 63V Polyester Capacitor

C2 100µF 25V Electrolytic Capacitor

D1,D2 1N4148 75V 150mA Diodes

IC1 7555 or TS555CN CMos Timer IC

R1 10K 1/4W Resistor

R2 47K 1/4W Resistor

R3 1K5 1/4W Resistor

LP1 1.5V 200mA Bulb

SW1 SPST Switch

B1 3V (Two 1.5V AA or AAA cells in series, etc.)

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Step Up Converter For 20 LEDs

The schema described here is a step-up converter to drive 20 LEDs, designed to be used as a home-made ceiling night light for a child’s bedroom. This kind of night light generally consists of a chain of Christmas tree lights with 20 bulbs each consuming 1 W, for a total power of 20 W. Here, in the interests of saving power and extending operating life, we update the idea with this simple schema using LEDs. 

Power can be obtained from an unregulated 12 V mains adaptor, as long as it can deliver at least about 330 mA.  The schema uses a low-cost current-mode controller type UCC3800N, reconfigured into voltage mode to create a step-up converter with simple compensation. By changing the external components the schema can easily be modified for other applications. To use a current-mode controller as a voltage-mode controller it is necessary to couple a sawtooth ramp (rising from 0 V to 0.9 V) to the CS (current sense) pin, since this pin is also an input to the internal PWM comparator.

Step-up Converter For 20 LEDs Circuit Diagram

The required ramp is present on the RC pin of the IC and is reduced to the correct voltage range by the voltage divider formed by R3 and R2. The RC network formed by R4 and C6 is dimensioned to set the switching frequency at approximately 525 kHz. The comparator compares the ramp with the divided-down version of the output voltage produced by the potential divider formed by R6 and R7. Trimmer P1 allows the output voltage to be adjusted. This enables the current through the LEDs to be set to a suitable value for the devices used. The UCC3800N starts up with an input voltage of 7.2 V and switches off again if the input voltage falls below 6.9 V. The schema is designed so that output voltages of between 20 V and 60 V can be set using P1.

This should be adequate for most cases, since the minimum and maximum specified forward voltages for white LEDs are generally between 3 V and 4.5 V. For the two parallel chains of ten LEDs in series shown here a voltage of between 30 V and 45 V will be required. The power components D1, T1 and L1 are considerably over specified here, since the schema was originally designed for a different application that required higher power. To adjust the schema, the potentiometer should first be set to maximum resistance and a multimeter set to a 200 mA DC current range should be inserted in series with the output to the LEDs. Power can now be applied and P1 gradually turned until a constant current of 40mA flows. The step-up converter is now adjusted correctly and ready for use.

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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.

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.

Source :  http://www.ecircuitslab.com/2012/01/simple-automatic-switch-for-audio-power.html

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Build a Stand by Power Circuit Diagram for Non Volatile Cmos Rams

This is  a simple Stand by Power Circuit diagram for Non Volatile Cmos Rams. To prevent loss of data when a CMOS RAM is switched from normal operation (Vcc = 5 volts) to stand-by mode (Vcc = VBAT) it must be ensured that the CS pin goes near the Vcc rail at all times. 

Ac coupling to the chip select is made through capacitor C, breaking the dc current path between Vqq (and hence VBAT) and the decoder output. So, whatever the impedance state of the decoder in power down, the battery will provide current only for the RAM, low enough to keep the voltage at CS near to V^.

Power Circuit Diagram

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Waterproof Directed Flashlight Ready For Any Objective

Anytime Id personally think about purchasing a brand-new light my personal thoughts introduced me back to a time when us just possessed any Maglite,or even the stock plastic range many of us experienced such as h2o. The actual Fenix Cree LED Flash light changed my thoughts about the approach My partner and i checked out the actual light. Directed highlights will be the tradition nowadays.Most like the Guided spotlights,because they are brighter,and much less cumbersome ultimately.
The potency of the actual Fenix Guided will be the obvious choice for people that should you prefer a brilliant and extremely tough light. This isnt the actual run of the mill flashlight. Wonderfully constructed from airplane rank T-S metal. 630 lumen is an incredible amount of radiance,and also the Fenix is said to be your Best Electric battery Brought Light on Earth!

The thing youll not be worried about,and that is through an massive area of gentle when you select.Which has a column projection associated with 984 Foot. youll be able to deal with a really significant region. Lookup and rescue teams like the Fenix.Income sign expensive unexpected emergency ,sos,and strobe signs,it really is perfect for missions.
An excellent accessory for your own urgent situation tool kit.Traveling out-of-doors inside bad weather isnt any location to do without standard life keeping items. The particular Fenix is additionally Water-proof,consequently absolutely no bother about the actual thunder storms.Stay the flash light up-right along with a reading through light.
The particular protective sprayed accurate wine glass contact lens is very not likely to ever split. Control switches are protected from your elements which has a plastic start. A lanyard along with shoulder strap include the sunshine,as well as Only two additional To Rings to be able to fasten h2o out there.
The particular Cree Directed light is exchangeable and definately will are Fifty,000 hrs. Twice Double a battery packs are all that is required in order to switch on the particular Fenix Directed. The particular Fenix LED Flash light can be vivid and also extraordinary.The quality and also the engineering allow this specific for you to stand out above all various other lighting in its discipline.
A solid perform gentle with spectacular lumen.There is little change continue being mysterious in a thick remember to brush environment. No problem stashing your own Brought torch away.Technology takes on a part while using Fenix also. Knowing how the precise setting you want.Your Fenix Guided flash light requires the anguish from changing the environment any time you hearth up.
Multiple choices learn how to options regulate electric battery consumption.The particular cleverest setting may be the powerful Turbo Function.The producer recommends at most Fifteen minutes at this setting.
In case you direct the stressful existence that requires that you have the greatest lighting effects.In case your straight into research,camping,walking kilometers inside the back-country ,or perhaps fixing the top in Only two am.You need to opt for standing and performance that will keep up.

Regardless of whether your certainly not planning to climb K2 to simply go away the face area on a board.The Fenix Guided flash light goes just about anyplace,and make others signaled simultaneously.Among the most secure alternatives on the marketplace.
The actual best battery pack brightest flashlight on this planet is a pretty remarkable application.Sector level material property,weather conditions immune,and also unexpected emergency flashing allow it to be crucial. Group the Fenix upwards along with be confident youve got every one of the firepower to be in any kind of setting and also control the actual darkness.The particular led light bulbs for home will give you the electricity in order to demand into any kind of scenario.

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Simple game for kids

This is simple game for kids.You can propose your Friends to bring this ring one end to another end.while your friends are bringing this ring one end to another end if it touch the coil the bulb will light up.Then he loses the game.the chance goes to another.If one could take the ring to another side that one can win this game.this method is so impotent to check you nerves.if you can do this patiently you have good health condition

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Temperature Detector For Fan Controller

The fan controller circuit for the Titan 2000 and other AF heavy-duty power amplifiers, has an output that sets a voltage if the fan controller reaches the end of its range. Since the controller responds to temperature, this signal is seen by the amplifier protection circuitry as an over temperature indication. The disadvantage of this output is that the maximum voltage for the fans is not constant, but depends on the load (number of fans, defective fans) and the mains voltage. This variation is caused by the fact that the supply voltage for the output stage is taken directly from the filtered transformer voltage.

If the fans should fail, for example, the maximum temperature limit would lie at a considerably higher level than the desired value. The accompanying circuit, which compares the magnitude of the fan voltage to a fixed reference value, has been developed to allow the maximum temperature to be reliably detected. This circuit is tailored for 12-V fans. The reference voltage is generated by the ‘micro power voltage reference’ D1 and the FET T1, which is wired as a current source. These components are powered directly from the applied fan voltage. The current source is set up to deliver approximately 50µA.

D1 can work with as little as 10µA. The supply voltage for the IC is decoupled by R10, C3 and C4, with D4 providing over voltage protection. A maximum supply voltage of 16 V is specified for the TLC271. This opamp works with a supply voltage as low as 3 V and can handle a common-mode voltage up to approximately 1.5 V less than the positive supply voltage. Accordingly, 1.2 V has been chosen for the reference voltage. The fan voltage is reduced to the level of the reference voltage by the voltage divider R2–R3–P1. The limits now lie at 11.2 V and 16.7V.

If you find these values too high, you can reduce R2 to 100 kΩ, which will shift the limits to 9.5 V and 14.2 V. The output of the voltage divider is well decoupled by C2. A relatively large time constant was selected here to prevent the circuit from reacting too quickly, and to hold the output active for a bit longer after the comparator switches states. A small amount of hysteresis (around 1 mV) is added by R4 and R5, to prevent instability when the comparator switches. D2 ensures that the magnitude of the hysteresis is independent of the supply voltage. Two outputs have been provided to make the circuit more versatile.

Output ‘R’ is intended to directly drive the LED of an optocoupler. In addition, transistor T2 is switched on by the output of the opamp via R7 and R8, so that a relay can be actuated or a protection circuit triggered using the ‘T’ output. The high-efficiency LED D3 indicates that IC1 has switched. It can be used as a new ‘maximum’ temperature’ indicator when this circuit is added to the fan controller. The circuit draws only 0.25 mA when the LED is out, and the measured no-load current consumption (with a 12.5V supply voltage) is 2.7 mA when the LED is on.

Resistors:

• R1 = 22kΩ
• R2 = 120kΩ
• R3 = 10kΩ
• R4,R6 = 1kΩ
• R5 = 1MΩ
• R7,R8 = 47kΩ
• R9 = 3kΩ9
• R10 = 100Ω
• P1 = 5kΩ preset

Capacitors:

• C1,C3 = 100nF
• C2 = 100µF 25V radial
• C4 = 47µF 25V radial

Semiconductors:

• D1 = LM385-1.2
• D2 = BAT85
• D3 = high-efficiency-LED
• D4 = zener diode 16V/1W3
• T1 = BF245A
• T2 = BC547B
• IC1 = TLC271CP

Miscellaneous:

• K1 = 2-way PCB terminal block, raster 5mm
• K2 = 3- way PCB terminal block, raster 5mm

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Fuel Reserve Indicator For Vehicles

Here is a straightforward circuit for monitoring the gasoline stage in vehicles. It offers an audiovisual indication when the gasoline stage drops alarmingly under the reserve degree, helping you to keep away from working out of petrol on the way. Nowadays autos come with a dash-mounted gasoline gauge meter that point outs the fuel degrees on an analogue display. The ‘reserve’ level is indicated with the help of a pink marking in some vehicles, but the needle motion in the path of the crimson marking is additionally complicated and no longer actual. This circuit displays the fuel tank under the reserve stage and warns thru LED indicators and audible beeps when the chance level is drawing near. 

Circuit diagram :

Fuel Reserve Indicator For Vehicles Circuit Diagram

The gas sensor system includes a tank-mounted waft sensor and a current meter (fuel meter), that are connected in sequence. The go with the flow-driven sensor hooked up to an interior rheostat offers excessive resistance when the tank is empty. When the tank is full, the resistance decreases, permitting extra current to cross in the path of the meter to give a higher studying. The gas monitoring circuit works by sensing the voltage model developed across the meter and prompts the beeper when the fuel tank is nearly empty. Its level A is hooked up to the input terminal of the fuel meter and point B is connected to the body of the car. The circuit consists of an op-amp IC CA3140 (IC1), two 555 timer ICs (IC2 and IC3) and decade depender CD4017 (IC4). 

Op-amp IC CA3140 is wired as a voltage comparator. Its inverting input (pin 2) obtains a reference voltage managed thru VR1. The non-inverting enter (pin 3) obtains a variable voltage tapped from the enter terminal of the fuel meter via resistor R1. When the voltage at pin 3 is better han at pin 2, the output of IC1 goes high and the green LED (LED1) glows. This situation is maintained until the voltage at pin three drops beneath that at pin 2. When this occurs, the output of IC1 swings from high to low, sending a low pulse to the set off pin of the monostable (usually held high by using R3) by manner of C1. The monostable set offs and its output goes high for a predetermined time according to the values of R5 and C2. With the given worths, the ‘on’ time will doubtless be around four minutes. 

The output of IC2 is used to power the astable circuit together with timer 555 (IC3) by implys of diode D2. Oscillations of IC3 are controlled with the help of R6, R7, VR2 and C4. With the given worths, the ‘on’ and ‘off’ time periods are 27 and 18 2nds, respectively. The pulses from IC3 are given to the clock enter (pin 14) of decade depender CD4017 (IC4) and its outputs go excessive one by way of one. When the circuit is swaped on, LED1 and LED2 glow in case your vehicle has adequate petrol within the tank. 

When the gasoline goes below the reserve stage, the output of IC1 goes low, LED1 flips off and a terrible set offing pulse is received at pin 2 of IC2. The output of IC2 goes excessive for round 4 minutes and all via this time frame, clock pin 14 of IC4 obtains the clock pulse (low to high) from the output of IC3. For the first clock pulse, Q0 output of IC4 goes high and the fairway LED (LED2) glows for round 50 2nds. On receiving the 2nd clock pulse, Q1 goes excessive to illuminate the yellow LED (LED3) and sound the buzzer for round forty five 2ds. This audio-visual sign warns you that the vehicle is working out of gasoline. On receiving the 0.33 clock pulse, LED3 and the buzzer go off. There is a niche of around two-and-a-half minutes before Q5 output goes excessive.

By the time Q5 goes excessive and the red LED (LED4) glows, 4 minutes elapse and the ability provide to IC3 is bring to an end. The output state at Q5 will no longer exchange except a low-to-high clock input is obtaind at its pin 14. Thus LED4 will glow constantly together with the beep. The continuous glowing of the pink LED (LED4) and the beep from the buzzer indicate that the car will run out of fuel very shortly. Q6 output of IC4 is related to its reset pin 15 via diode D3. This means that after ‘on’ state of Q5, the count will at all times begin from Q0. Capacitor C5 presents power-on reset to IC4 when switch S1 is closed. The output of IC1 can additionally be related to reset pin of IC4 by means of diode D1 (1N4148). So when your car is refueled above the reserve stage, LED2 glows to point that the tank has enough gas.

IC5 presents regulated 12V DC for right kind functioning of the circuit even when the battery is charged to greater than 12V. The circuit can be assembled on a perforated board. Adjust VR1 till the voltage at pin 2 of IC1 drops to 1.5V. When level A is hooked up to the fuel meter (fuel gauge) terminal that goes to the gasoline sensor, inexperienced LEDs (LED1 and LED2) glow to indicate the traditional gasoline degree. VR2 may additionally be varied to set the ‘on’ time frame of IC3 at round 20 2ds. Enclose the circuit in a small case and mount on the dashboard the use of adhesive tape. The circuit works most effective in automobiles with poor grounding of the physique.

Author : D. Mohan Kumar

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Video Switch for Intercom System

Nowadays a lot of intercom units are  equipped with video cameras so that you can  see as well as hear who is at the door. Unfortunately, the camera lens is perfectly placed  to serve as a sort of support point for people  during the conversation, with the result that  there’s hardly anything left see in the video  imagery.  One way to solve this problem is to install two cameras on the street side instead only  one, preferably some distance apart. If you  display the imagery from the two cameras  alternately, then at least half of the time you  will be able to see what is happening in front  of the door. Thanks to the video switch module described  here, which should be installed on the street  side not too far away from the two cameras,  you need only one monitor inside the house and you don’t need to install any additional video cables.

 

Circuit diagram :

Video Switch for Intercom System Circuit Diagram

Along with a video switch, the circuit includes  a video amplifier that has been used with  good results in many other Elektor projects,  which allows the brightness and the contrast  to be adjusted separately. This amplifier is  included because the distance between the  street and the house may be rather large, so it is helpful to be able to compensate for cable attenuation in this manner.  The switch stage is built around the well  known 4060 IC, in which switches IC2a and  IC2d alternately pass one of the two signals to  the output. They are driven by switches IC2b and IC2c, which generate control signals that  are 180 degrees out of phase. The switching rate for the video signals is  determined by a clock signal from an ‘old  standby’ 555 IC, which causes the signals to  swap every 2 seconds with the specified com ponent values.

 

Naturally, this circuit can also used in many other situations, such as where two cameras are needed for surveillance but only one video cable is available. 

 

 

 

 http://streampowers.blogspot.com/2012/06/video-switch-for-intercom-system_11.html

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Speaker Headphone Switch Circuit Diagram For Computers

If you need to use a headset with your PC, then you will know how frustrating it is continuously swapping over speaker and microphone cables. This is even worse if the PC is parked in a dark corner and the hard-to-read writing on the sound card sockets is covered in dust. This simple switch box eliminates all these problems. It sits on top of the desk and connects to the PC with stereo one-to-one cables.

On the rear of the box are sockets for the PC speaker and microphone connections and the existing speakers. On the front of the box are the sockets for the headset microphone and headphones, an input for an external microphone and two switches. One switch is used to direct the sound card output from the PC to either the existing speakers or the headphones.

Circuit diagram:

Speaker-Headphone Switch Circuit Diagram

The second switch connects either the headset microphone or the external microphone to the input socket of the PC sound card. The switches used were 3 position 4 pole rotary switches with the last pole unused and adjusted for 2-position operation. All sockets were stereo 3.5mm types. This multiple switching arrangement is very flexible and is especially handy if you want to use an external microphone while monitoring with headphones. The ground wire as well as the left and right wires are all switched to prevent noise that could otherwise be induced into the microphone input through joining separate earths. For the same reason, a plastic case is used so that the earths of the sockets are not shorted together as would happen with a metal case. You will require two additional short stereo extension cables to connect the box to the PC.

Author: Leon Williams - Copyright: Silicon Chip Electronics

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TDA1072A for AM receiver circuit

This TDA1072A integrated AM receiver circuit performs the active and part of the filtering functions of an AM radio receiver. TDA1072A is intended for use in mains-fed home receivers and car radios. The circuit design can be used for oscillator frequencies up to 50 MHz and can handle r. f. signals up to 500 mV. R.F. radiation and sensitivity to interference are minimized by an almost symmetrical design. The voltage-controlled oscillator provides signals with extremely low distortion and high spectral purity over the whole frequency range even when tuning with variable capacitance diodes. When required, band switching diodes can easily be applied. Selectivity is obtained using a block filter before the i.f. amplifier. The figure of the circuit is shown by the figure below;

The feature of TDA1072A is;
The inputs protected against damage by static discharge. Gain-controlled r.f. stage. Separately buffered, voltage-controlled and temperature-compensated oscillator, designed for simple coils. Internal generation of a.g.c. voltage with possibility of second-order filtering. Buffered field strength indicator driver with short-circuit protection.

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Contrast Control for LCDs

The adjustment control for the contrast of an LC-Display is typically a 10-k potentiometer. This works fine, provided that the power supply voltage is constant. If this is not the case (for example, with a battery power supply) then the potentiometer has to be repeatedly adjusted. Very awkward, in other words. The circuit described here offers a solution for this problem. The aforementioned potentiometer is intended to maintain a constant current from the contrast connection (usually pin 3 or Vo) to ground. A popular green display with 2x16 characters ‘supplies’ about 200 µA. At a power supply voltage of 5 V there is also an additional current of 500 µA in the potentiometer itself. Not very energy efficient either. Now there is an IC, the LM334, which, with the aid of one resistor, can be made into a constant current source. The circuit presented here ensures that there is a current of 200 µA to ground, independent of the power supply voltage. By substituting a 2.2-k? potentiometer for R1, the current can be adjusted as desired.

Circuit diagram:The value of R1 can be calculated as follows: R1 = 227x10-6 x T / I. Where T is the temperature in Kelvin and I is the current in ampères. In our case this results in:

R1 = 227x10-6 x 293 /
(200x10-6)
R1 = 333R

Note that the current supplied by the LM334 depends on the temperature. This is also true for the current from the display, but it is not strictly necessary to have a linear relationship between these two. Temperature variations of up to 10° will not be a problem however. This circuit results in a power saving of over 25% with an LCD that itself draws a current of 1.2 mA. In a battery powered application this is definitely worth the effort! In addition, the contrast does not need to be adjusted as the battery voltage reduces. When used with LCDs with new technologies such as OLED and PLED it is advisable to carefully test the circuit first to determine if it can be used to adjust the brightness.

Circuit diagram:

Contrast Controller Circuit Diagram For LCDs

The value of R1 can be calculated as follows: R1 = 227x10-6 x T / I. Where T is the temperature in Kelvin and I is the current in ampères. In our case this results in:

• R1 = 227x10-6 x 293 /
• (200x10-6)
• R1 = 333R

Note:

• The current supplied by the LM334 depends on the temperature. This is also true for the current from the display, but it is not strictly necessary to have a linear relationship between these two. Temperature variations of up to 10° will not be a problem however. This circuit results in a power saving of over 25% with an LCD that itself draws a current of 1.2 mA. In a battery powered application this is definitely worth the effort! In addition, the contrast does not need to be adjusted as the battery voltage reduces. When used with LCDs with new technologies such as OLED and PLED it is advisable to carefully test the circuit first to determine if it can be used to adjust the brightness.

Author: Heino Peters - Copyright: Elektor Electronics

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Pre Amplifier Circuit for Oscilloscope

An oscilloscope amplifier with 20 dB voltage gain is provided by this circuit with a frequency range from 0.5 to 50 MHz. By increasing the value of the 0.05 uF capacitor or try removing the capacitor, we can extend the low frequency response of this circuit. This is the figure of the circuit;

A particularly small level of input noise is delivered by this circuit, measured at approximately 20uA over a bandwidth range at 15 MHz. By adjusting the gain potentiometer connected between pins 3 and 10, then adjust the 1-KΩ trimmer potentiometer for an exact voltage gain of 10 are the ways to calibrate the gain. This helps preserve the scale factor of the oscilloscope.

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