Custom Search

Sponsor Links

Visitor Map


Tuesday, June 30, 2009

Simple USB Lamp Circuit

This is a simple USB powered lamp that can be used to light in your desktop during power supply failures. This is a figure of the circuit connection. The explanation of the principle work is in below.

The operation of USB lamp circuit is from the 5 V available from the USB port. The 5V from the USB port is passed through current limiting resistor R2 and transistor Q1. The base of transistor Q1 is grounded via R1 which provides a constant bias voltage for Q1 together with D2.The diode D1 prevents the reverse flow of current from battery.C1 is used as a noise filter. Two white LED’s are used here for the lamps, you can also use a 2 V torch bulb instead of LED’s. LED D3 indicates connection with USB port.

There are notes for this circuit. The first is USB port is only able to provide up to 100 mA current. So, don’t overload the circuit with more no of LED’s. Second, before wiring the circuits confirm the positive and ground leads of USB by a multi meter. The third is switch S1 can be used to turn on the lamp.

Simple Adjustable Frequency Oscillator Circuit

This is a very simple oscillator circuit that based on a 555 timer IC to generate square wave of frequency that can be adjusted by a potentiometer. With values given the frequency can be adjusted from a few Hz to several KHz. To get very low frequencies replace the 0.01uF capacitor with a higher value. The figure of the circuit is following in below.

The operation of the circuit is follow by the formula to calculate the frequency that is given in below:

1/f = 0.69 x C x (R1 + 2*R2)
And the duty cycle is given by:
% duty cycle = 100*(R1+R2)/(R1+ 2*R2)

In order to ensure a 50% (approx.) duty ratio, R1 should be very small when compared to R2. But R1 should be no smaller than 1K. A good choice would be make with R1 in kilo ohms and R2 in mega ohms. You can then select C to fix the range of frequencies.

Thursday, June 25, 2009

The Simple Wide Band VHF preamplifier circuit

This is a simple wide band VHF preamplifier that based on PNP transistor. This circuit is inexpensive circuit. The circuit may be used as a signal booster with VHF receivers whose front end suffers from low sensitivity (such as many valve and army surplus types). The frequency range of the preamplifier is roughly from 75MHz to 150MHz. This is the figure of the circuit.

The operation of the circuit is the two inductors in the circuit are home made. L1 consists of 10turns of 24SWG enameled copper wire; the internal diameter is 3mm, no core. Inductor L2 has 13 turns of the same wires, and an internal diameter of 5mm; no core is used either. A construction tip: close-wind the inductors using 3 and 5mm drill bits respectively as temporary formers. The prototype of the preamplifier was successfully used with an 88-108 MHz FM broadcast receiver and a 2-metre VHF ham receiver. The preamplifier draws about 2.5mA from a 5-volt supply.

Simple Variable Voltage Regulator Using LM317T

This is a simple circuit that can use as voltage regulator. This circuit is adjusts by LM317T as core of the circuit. LM317T is adjustable 3 terminal positive voltage regulators capable of supplying in excess of 1.5 amps over an output range of 1.25 to 37 volts. The figure of the variable voltage regulator using LM317T is in below;

The principle work of this circuit is output voltage is set by two resistors R1 and R2 connected as shown below. The voltage across R1 is a constant 1.25 volts and the adjustment terminal current is less than 100uA. The output voltage can be closely approximated from Vout=1.25 * (1+(R2/R1)) which ignores the adjustment terminal current but will be close if the current through R1 and R2 is many times greater. A minimum load of about 10mA is required, so the value for R1 can be selected to drop 1.25 volts at 10mA or 120 ohms. Something less than 120 ohms can be used to insure the minimum current is greater than 10mA. The example below shows a LM317 used as 13.6 volt regulator. The 988 ohm resistor for R2 can be obtained with a standard 910 and 75 ohm in series.

When power is shut off to the regulator the output voltage should fall faster than the input. In case it doesn't, a diode can be connected across the input/output terminals to protect the regulator from possible reverse voltages. The power transformer should be large enough so that the regulator input voltage remains 3 volts above the output at full load, or 16.6 volts for a 13.6 volt output.

Simple FM Antenna Booster Circuit

This is a low cost fm antenna booster that can be used to listen to program from distant FM stations clearly. The antenna fm booster circuit comprises a common-emitter tuned RF preamplifier wired around VHF/UHF transistor 2SC2570 (C2570). This is the schematic of the simple FM Antenna Booster.

Assemble the circuit on a good quality of printed circuit board. Adjust input/output trimmers (VC1/VC2) for maximum gain. Input coil L1 consists of four turns of 20SWG enameled copper wire (slightly space wound) over 5mm diameter former. It is tapped at the first turn from ground lead side. Coil L2 is similar to L1, but has only three turns. Pin configuration of transistor 2SC2570 is shown in the fm antenna booster schematic.

Simple AM/FM/SW Active Antenna Using MOSFET

This is a simple circuit that can be used to an active antenna. This circuit is based on MOSFET to be core of operation. The MOSFET that used is MPF102. This is the figure of the active antenna.
The circuit can used to AM, FM or SW frequency. On the short wave band this circuit is comparable to a 20 to 30 foot wire antenna.

This circuit is designed to be used on receivers that use to an-tune the wire antennas, such as inexpensive units and car radios. The basic operation of this circuit is L1 can be selected for the application. A 470uH coil works on lower frequencies (AM), for short wave, try a 20uH coil. The unit can be powered by a 9 volt battery. If a power supply is used, bypass the power supply with a .04uF capacitor to prevent noise pickup. The antenna used on this circuit is a standard 18" telescoping type. Output is taken from jack J1 and run to the input on the receiver.
Source of the figure: "Popular Electronics" Magazine, Jul, 89 issue. (C)Copyright Gernsback Publications, Inc., 1989

Simple Adjustable Voltage Source Circuit

This is a simple but less efficient method of controlling a DC voltage is to use a voltage divider and transistor emitter follower configuration. The figure is illustrated the principle work of the circuit.

The principle of this circuit is using a 1K pot to set the base voltage of a medium power NPN transistor. The collector of the NPN feeds the base of a larger PNP power transistor which supplies most of the current to the load. The output voltage will be about 0.7 volts below the voltage of the wiper of the 1K pot so the output can be adjusted from 0 to the full supply voltage minus 0.7 volts. Using two transistors provides a current gain of around 1000 or more so that only a couple milliamps of current is drawn from the voltage divider to supply a couple amps of current at the output.

There are notes for attention. This circuit is much less efficient than the 555 timer dimmer circuit using a variable duty cycle switching approach. In the figure above, the 25 watt/12 volt lamp draws about 2 amps at 12 volts and 1 amp at 3 volts so that the power lost when the lamp is dim is around (12-3 volts * 1 amp) = 9 watts. A fairly large heat sink is required to prevent the PNP power transistor from overheating.

Friday, June 12, 2009

A Lighting Point Circuit

It is a simple circuit. Before install the light point we must create this circuit. An electrical circuit as mentioned before is just a loop that current travels through continuously non stop. To break this loop we use a switch. The continuous flow of electricity will light up any light that has been designed to work with the specified amount of current or electrical supply. This is the concept of the light point.

How the circuit is operates? With reference to the diagram above, run 2 wires from the main switch panel. It would be advisable to use two different color coded wires to easily differentiate where the wire go. In this example we shall use the red wire for the live wire and the black wire for the neutral. The red wire or the live wire goes to the switch terminal, and the black or neutral wire goes to the light holder’s terminals. From the switch, run another wire to the light holder’s other terminal. This is the switch wire. You can see the Live wire and the Switch wire is actually one single piece of wire, cut off into half by the switch. If the switch is ON, it connects the wire back, if it is OFF, the wire gets cut off again. Thus you can switch the lights ON and OFF. At the mains, (Make sure all the Mains have been switched off), connect the red wire to any one of the sub circuit breakers. The black wires goes to the neutral link which in fact is a thick copper strip with all the neutral wires connected together. Just try to squeeze another one in.

Tuesday, June 2, 2009

Simple Water Alarm Circuit

This simple water alarm circuit is a simple circuit that used to indicate level of drying in some place. The simple water alarm is based on 555 timer IC and a transistor. The figure show how is the circuit work. 555 IC is used to be an unstable oscillator and the transistor powered the circuit using emitter current. Transistor that can be used is BC109C. This circuit can controlled by automatic if connected with microcontroller. Principle work of this circuit is when under dry conditions, the transistor will have no bias current and be fully off. As the probes get wet, a small current flow between base and emitter and the transistor switches on. A larger current flows in the collector circuit enabling the 555 oscillator to sound.

An On/Off switch has provided and remembered to use a non-reactive metal for the probe contacts. Gold or silver plated contacts from an old relay may be used, however a cheap alternative is to wire alternate copper strips from a piece of ferro board. These will eventually oxidize over but as very little current is flowing in the base circuit, the higher impedance caused by oxidization is not important. No base resistor is necessary as the transistor is in emitter follower, current limit being the impedance at the emitter (the oscillator circuit).

Simple Speaker Microphone Circuit

This circuit allows you to use a cheap and a simple loudspeaker as a microphone. This circuit is based on a transistor BC109C. Sound waves reaching the speaker cone cause fluctuations in the voice coil. The voice coil moving in the speaker magnetic field will produce a small electrical signal. The circuit is designed to be used with an operating voltage between 6 and 12 volts dc. This is the picture of the circuit;

How is this circuit work? The first transistor operates in common base mode. This has the advantage of matching the low input impedance of the speaker to the common base stage, and secondly has a high voltage gain. The second stage is direct coupled and operates in emitter follower. Voltage gain is slightly less than unity, but output impedance is low, and will drive long cables.

Speech quality is not as good compared to an ordinary or ECM microphone, but quite acceptable results can be obtained. Speaker cones with diameters of 1 inch to 3 inches may be used. Speaker impedance may be 4 ohm to 64 ohm. The 8.2 ohm resistor value may be changed to match the actual speakers own impedance.

Simple Op-Amp Radio Circuit

This circuit is a simple design for crystal radio. Audio amplifier for this radio is fairly sensitive and receives several strong stations with a minimal 15 foot antenna. Longer antennas will provide a stronger signal but the selectivity will be worse and strong stations may be heard in the background of weaker ones. Using a long wire antenna, the selectivity can be improved by connecting it to one of the taps on the coil instead of the junction of the capacitor and coil.

The operation of this circuit is the inductor was wound with 200 turns of #28 enameled copper wire on a 7/8 diameter, 4 inch length of PVC pipe, which yields about 220 uH. The inductor was wound with taps every 20 turns so the diode and antenna connections could be selected for best results which turned out to be 60 turns from the antenna end for the diode. The diode should be a germanium 1N34A type for best results, but silicon diodes will also work if the signal is strong enough.

The carrier frequency is removed from the rectified signal at the cathode of the diode by the 300 pF C and the audio frequency is passed by the 0.1uF C to the non-inverting input of the first op-amp which functions as a high impedance buffer stage. The second op-amp stage increases the voltage level about 50 times and is DC coupled to the first through the 10K resistor. If the pairs of 100K and 1 Meg resistors are not close in value 1% and we may need to either use closer matched values or add a capacitor in series with the 10K resistor to keep the DC voltage at the transistor emitter between 3 and 6 volts. Another approach would be to reduce the overall gain with a smaller feedback resistor (470K). High impedance headphones will probably work best, but walkman stereo type headphones will also work. Circuit draws about 10 mA from a 9 volt source.

Simple Current Loop Interface Circuit

This is a very simple circuit to interface a current loop sensor to an input which is designed for a voltage, such as that from a standard potentiometer. The circuit is based on five transistors. They will amp the input that is entered the circuit. This is the figure of the circuit.

The operation of this circuit is Tr1 and Tr2 are a current mirror arranged to source about 1mA into the sensor, via Tr2. This current can be adjusted by the preset to 'back-off' the zero position current. This allows an electrical zero adjust (in practice we usually prefer to use the throttle's mechanical zero adjust). Tr3, 4 and 5 are a second mirror which reflect the sensor's output current (less the backed off zero portion) into the 4K7 resistor is a resistor is a current to voltage converter. We have therefore developed an output voltage proportional to throttle position and it has the same 3 wires as a standard potentiometer.

The throttle itself consists of a coil and some electronics with a steel jacketed brass slug which is moved in and out of the coil by the throttle movement. The assembly has only two contacts and draws a current of between 600 micro amps and 2 milliamps: the current varies with slug position as the throttle is moved. As such it is a system which borrows much from the industrial 4-20mA current loop sensor standard.

Simple 12 Volt Lamp Dimmer Circuit

This is a simple design schematic for lamp. This circuit based on 555 IC that’s used to unstable oscillator. 12 volt / 2 amp lamp dimmer that can be used to dim a standard 25 watt automobile brake or backup bulb by controlling the duty cycle of 555 IC. This is a picture of the schematic;

The operation of this circuit is when the wiper of the potentiometer is at the uppermost position, the capacitor will charge quickly through both 1K resistors and the diode, producing a short positive interval and long negative interval which dims the lamp to near darkness. When the potentiometer wiper is at the lowermost position, the capacitor will charge through both 1K resistors and the 50K potentiometer and discharge through the lower 1K resistor, producing a long positive interval and short negative interval which brightens the lamp to near full intensity. The duty cycle of the 200 Hz square wave can be varied from approximately 5% to 95%. The two circuits below illustrate connecting the lamp to either the positive or negative side of the supply.

Monday, June 1, 2009

A Simple PWM Circuit Using 555 Timer IC

PWM is the most common method of speed control to control DC motor. It is a one fundamental of control system in programming interface or robotics. PWM is the process of switching the power to a device on and off at a given frequency, with varying on and off times. These on and off times are referred to as “duty cycle”. This is a simple design of PWM circuit that using 555 IC. In the figure shows the wave forms of 10%, 50%, and 90% duty cycle signals.

How is this circuit work? When this circuit powers up, the trigger pin is L as capacitor C1 is discharged. It will begin the oscillator cycle, causing the output to go H. If the output is H, capacitor C1 begins to charge through the right side of R1 and diode D2. And then the voltage on C1 reaches 2/3 of +V, the threshold (pin 6) is activated, which in turn causes the output (pin 3), and discharge (pin 7) to go LOW. If the output (pin 3) goes L, capacitor C1 starts to discharge through the left side of R1 and D1. When the voltage on C1 falls below 1/3 of +V, the output (pin 3) and discharge (pin 7) pins go H, and the cycle repeats.

Pin 5 is not used for an external voltage input, so it is bypassed to ground with a 0.01uF capacitor. For note the configuration of R1, D1, and D2. Capacitor C1 charges through one side of R1 and discharges through the other side. The sum of the charge and discharge resistance is always same, therefore the wave length of the output signal is constant. Only the duty cycle varies with R1. The overall frequency of PWM signal in this circuit is determined by the values of R1 and C1. In the schematic above, this has been set to frequency 144 Hz.

A Simple Crossover Circuit for Tweeter

A single coil speaker is not good in handling high and low frequency at the same time. If we could filter out the low frequency and play it through a tweeter, it will produce more sound quality than using a single speaker. In this figure shows the answer for the problem in above. This is a simple design circuit for protected thee voltage and current in tweeter speaker.

The concept of operation this circuit is the speaker that can protected is tweeter with 4 or 8 ohm impedance. R1 is a potentiometer resistor that used to adjust matching the tweeter speaker output level to that of woofer. R1 should be rated more than 2 Watts.

A Simple 3 Band Equalizer

This is a simple 3 band graphic equalizer circuit that’s built by a single op amp IC LF351 IC and few passive components. The component values of this circuit are not very critical and can be replaced with nearest values with a little loss on the performance. This is feature make it easy to be assembled from your junk box. This is a figure of the circuit;

How is the simple 3 band graphic equalizer work? The op amp LF351 is wired to operate in three frequency ranges-high, medium and low. The circuit is designed such that the circuit produces +/-20 dB boost or attenuation for 50Hz,1KHz and 10Khz by varying POT’s R3, R6 and R9.The maximum amplification for any of these bands at maximum supply voltage is 20dB.The op amp LF 351 is wired as an inverting amplifier whose response to frequencies 50Hz,1Khz and 10KHz can be varied by adjusting POT’s R3,R6 and R9.