VHF (100-450 MHz) 250W Power Amplifier

Two octave wideband amplifier (covering both the civil and military airbands between 100 and 450 MHz), equipped with two MOSFET devices, which is capable of generating 250 W of output power are given on this design procedures and measurement results report. One of the two octave wideband amplifier has to use the device s with the output capacitance reduced to the utmost minimum in order to achieve a good broadband capability. It was possible to obtain a respectable power gain of more than 10 dB throughout the whole band while applying PHILIPS’ BLF548 MOSFETs. The BLF548 is a balanced N-channel enhancement mode vertical D-MOS transistor in a SOT262 package. This device is especially designed for use in wideband amplifiers up to 500 MHz. 150 W nominal output power at a supply voltage of 28 Volts can be delivered by the transistor. The attainable bandwidth will exceed 300 MHz due to the low output capacitance.

Notes

1. American Technical Ceramics type 100B or capacitor of same quality.

2. American Technical Ceramics type 175B or capacitor of same quality.

3. The striplines are on a double copper-clad PCB with P.T.F.E. fibre-glass dielectric (er = 2.2); thickness 1/32 inch.

4. T2 and T3 are equipped with a Toroidal core, grade 4C6 (cat.no. 4322 020 97171).

Fan Speed Controller Using Op-Amp

We can make an enhancement to DAC drive fan controllers with the use of an external amplifier that closes the loop around the tachometer. Essentially linear control over the full range of 8 bit DAC codes from 0 to 255 is provided by this enhancement. This only requires a little signal conditioning and a suitable amplifier arrangement since the tachometer is already there. Figure a shows us that the tachometer pulses are conditioned such that all pulse width information is removed (differentiated) and only pulse rate information remains. Fan speed or frequency is represented by this pulses. Than, this pulse is used as the feedback to an integrating motor control amplifier.

To provide pulses just shorter than the duration of the shortest tachometer pulse at full fan speed, the time constant of the differentiator is initially set. Usually, this will provide a very little gain. We can increase the gain by decreasing the value of either R2 or C1. We have to set the gain so the fan just achieves full speed with the full DAC output applied to the input of the amplifier circuit.

To provide a smooth response to speed changes without any overshoot or hunting, the time constant of the integrator is set. Typically, this is done empirically with the actual system and fan. The response of the amplifier with the integration capacitor C2 at two values, 0.1uF and 1.0 uF is depicted by the plots in figure b and figure c. Either value meets the requirement for stability which dictates less than 25% overshoot

Electric Field Detector with 6 Million Gain Transistor

This is a circuit that can produce 6 million gain. As well as detecting general electric noise, this circuit can be used to detect “mains hum,” the presence of your hand without any direct contact, and detect static electricity. Here is the schematic diagram of the circuit:

The mains cable can be located by this circuit by moving it across any wall. The gain is achieved from 200 x 200 x 200. Since the circuit detects very weak electric field, it might look like ghost detector because electric field has weird pattern sometimes.

Siren Driver Circuit

This is a driver circuit for siren. This circuit usually used for car alarms. To build this circuit, we use VD-MOS FETs. This circuit receives 12 v supply from battery. A microprocessor sends complementary pulse waveforms to the driver circuit as inputs. Here is the circuit :

This circuit uses two PHC21025 which each of them contains two FETs. Two BSN20 VD-MOS FETs in small SOT23 packages also used in this circuit. The maximum configuration of this circuit needs eight components and the minimum configuration of this circuit needs six components

Magnetic Reed Switch Alarm

This circuit is made to be an alarm, both for home and handbags. If it is installed for home it will placed on door or windows, and if it is installed for bags or handbags it will placed in the bag. This circuit consists of a small magnet and a reed switch. If the magnet looses its contact with the reed switch, SW1 opens, the circuit starts oscillating and the loudspeaker emits a loud alarm sound.so this circuit suitable for use as an anti-theft alarm.

This circuit uses A complementary transistor-pair which is wired as a high efficiency oscillator, directly driving a small loudspeaker. Low part-count and 3V battery supply enable a very compact construction.



Notes :



The loudspeaker’s dimensions are limited only by the box that contain it.

An on-off switch is unnecessary because the stand-by current drawing is less than 20µA.

Current consumption when the alarm is sounding is about 100mA.

If the circuit is used as anti-bag-snatching, SW1 can be replaced by a 3.5mm mono Jack socket and the magnet by a 3.5mm.

Do not supply this circuit with voltages exceeding 4.5V: it will not work and Q2 could be damaged.

Audio Speech Compressor

There are many low power SSB rigs and kits don’t have any real speech processor circuitry, although there is a built in speech processor in most modern HF. Speech processing is an important thing, when the SSB is operated at low power to get through the QRM. Speech processing can be done by this circuit. This is a simple and low cost circuit but it can perform well. This circuit includes the microphone element. So, we can assemble complete speech processor microphone in an old defunct desk mike. Here is the schematic diagram of this circuit :

This circuit contains a feedback amplifier and an audio preamplifier. S1 should be closed, to use the speech processor. R5 is used as the gain control for basic preamplified microphone that is given by Leaving S1 open. Q2 is triggered to conduct by voice peaks from the feedback amplifier, when S1 is closed. It causing the gate of Q1 to become negative. The resistance between the source and drain of Q1 substantially increase due to the gate of Q1 become negative. During very large voice peaks, Resistor R1 allows a small amount of audio to pass. to smooth out the voice, this circuit uses capacitor C2. C6 gives a time delay, so we can do the fast attack, slow release action. R7 can be replaced by a potentiometer. So we have variable speech compression control. [Source: Radio Amateur Society of Norwich]

Random Blinking (Flashing) LED

We can using this circuit to make the LEDs blink in a random pattern according to the slight differences in the three Schmitt Trigger oscillators.

The CD4511 is BCD to 7 segment Driver, so the pattern of the led is actually the come from seven segment representation. Arrange the LEDs to be far from seven segment pattern if you want to avoid people analyze your circuit. The randomness is based on the frequency difference because the 22uF and 47k resistors that determine the frequency have at least 5% tolerance.

SA58672 Small Class-D Audio Amplifier for Mobile Device

This is a circuit of SA58672 Small Class-D Audio Amplifier. This circuit is suitable for mobile device. It has maximum output power of 3.0 W for a 4ohm load and 1.7W for 8ohm load with power supply of 5V. If we uses 3.6 V power supply, the maximum output power is 900mW with 8ohm load. Here is the circuit :

Using 9-bump Wafer Level Chip Scale Package (WLCSP), the SA58672UK save space in portable designs, because it measures only 1.66 x 1.71 x 0.6 mm.

This circuit produces better overall audio performance because it has improved RF rectification and immunity to noise. The SA58672UK is suitable for cellular handsets or wireless and other portable audio application because it has fast start-up time of 7 ms eliminates pop-on sounds. [Source: NXP Application Note]

Small Amplifier Using Transistors

When audio is detected, the output is push-pull and consumes less than 3mA (with no signal) but drives the earpiece to a very loud level. It’s extremely difficult to set up because the whole circuit is DC coupled. Basically you don’t know where to start with the biasing. 8k2 between the emitter of the first transistor and 0v rail and the 470R resistor are the two most critical component.

The emitter voltage on the BC 547 is set by the 8k2 across the 47u and this turns it on. To call the driver transistor, the collector is directly connected to the base of a BC 557. Current flow through the 1k and 470R resistors so that the voltage developed across each resistor turns on the two output transistors is caused by these transistors and the output of BC 557 are now turned on. The end result is mid-rail voltage on the join of the two emitters.Major negative feedback is provided by 8k2 feedback resistor while the 330p prevents high-frequency oscillations occurring. [Source: Talking Electronics]

Discrete 9-12V Microphone Pre-Amplifier

This is a microphone pre-amplifier circuit that use discrete components. The gain of this circuit is 100 and should be enough for most microphones. It is set by the ratio of the 10k resistor to the 100R. As common-emitter amplifiers, This circuit uses two directly coupled transistors. Here is the schematic diagram of circuit:

Please note that this circuit has no bias voltage source, so you can’t use with condenser type microphones. You can use this circuit with dynamic type microphone, or condenser electret module with active circuit inside (any microphone which is equipped with battery inside can be used).

12V Inverter Circuit Using 4013

This circuit is a circuit diagram 12V inverter is very easy to build, cheap components that many electronics hobbyists may even already have. Though it is possible to build a more powerful circuit, the complexity caused by the very heavy currents to be handled on the low-voltage side leads to circuits. The circuit diagram of 12v inverter is easy to follow. A classic 555 timer chip, identified as IC1, is configured as an astable multivibrator at a frequency close to 100 Hz, which can be adjusted accurately by means of potentiometer P1. It is used to drive a D type flip-flop produced using a CMOS type 4013 IC. This produces perfect complementary squarewave signals (in antiphase) on its Q and Q outputs suitable for driving the output power transistors. The following is a schematic drawing:

 

As the output current available from the CMOS 4013 is very small, Darlington power transistors are used to arrive at the necessary output current. We have chosen MJ3001s from the now defunct Motorola (only as a semi-conductor manufacturer, of course!) which are cheap and readily available, but any equivalent powerDarlington could be used.



These drive a 230 V to 2 × 9 V centre tapped transformer used ‘backwards’ to produce the 230 V output. The presence of the 230 VAC voltage is indicated by a neon light, while a VDR (voltage dependent resistor) type S10K250 or S07K250 clips off the spikes and surges that may appear at the transistor switching points.



12 Inverter Parts List

Resistors

R1 = 18k?
R2 = 3k?3
R3 = 1k?
R4,R5 = 1k?5
R6 = VDR S10K250 (or S07K250)
P1 = 100 k? potentiometer

Capacitors

C1 = 330nF
C2 = 1000 ?F 25V

Semiconductor

T1,T2 = MJ3001
IC1 = 555
IC2 = 4013

Miscellaneous

LA1 = neon light 230 V
F1 = fuse, 5A
TR1 = mains transformer, 2×9V 40VA (see text)

The Darlington transistors should be fitted onto a finned anodized aluminium heat-sink using the standard insulating accessories of mica washers and shouldered washers, as their collectors are connected to the metal cans and would otherwise be short-circuited. An output power of 30 VA implies a current consumption of the order of 3 A from the 12 V battery at the ‘primary side’. So the wires connecting the collectors of the MJ3001s [1] T1 and T2 to the transformer primary, the emitters of T1 and T2 to the battery negative terminal, and the battery positive terminal to the transformer primary will need to have a minimum crosssectional area of 2 mm2 so as to minimize voltage drop. The transformer can be any 230 V to 2 × 9 V type, with an E/I iron core or toroidal, rated at around 40 VA.

Properly constructed on the board shown here, the 12 inverter circuit should work at once, the only adjustment being to set the output to a frequency of 50 Hz with P1. The circuit should not be too difficult to adapt to other mains voltages or frequencies, for example 110 V, 115 V or 127 V, 60 Hz. The AC voltage requires a transformer with a different primary voltage (which here becomes the secondary), and the frequency, some adjusting of P1 and possibly minor changes to the values of timing components R1 and C1 on the 555.

Preamp + Tone Control Circuit Using Transistor

This circuit is a circuit diagram preamp and tone controls are combined in a single series. Series preamp and tone controls are using the transistor as a control. In the picture below P1 to control the volume level, to control the level of P2 and P3 for Bass control Treble level. This circuit is a circuit diagram mono channel, built a similar circuit to make this circuit stereo. The following is a schematic drawing:

Component:

R1__________220K
R2__________100K
R3__________2K7
R4 R5_______8K2
R6__________4K7
R7, R8, R13___2K2
R9__________2M2
R10, R11_____47K
R12_________33K
R14_________470R
R15_________10K
R16_________3K3



C1, C2, C9____470nF 63V

C3, C4_______47nF 63V

C5, C6_______6n8 63V

C7__________10?F 63V

C8, C10______22?F 25V

C11_________470?F 25V



Q1, Q3_______BC550C Low noise NPN 45V 100mA High gain

TransistorsQ2__________2N3819 General-purpose N-Channel FET

FM Tracking Transmitter Using a 555 Timer

Circuit diagram is designed for tracking transmitter audio tone in FM frequency band. Circuits that can be used the signal transmitter or remote control transmitter. In circuits that use only components that are available. Transmitter’s range is 100 m in the distance using the 9V power supply and matching the antenna. Circuit diagram is built by IC timer 555 to produce audio and tone based on the JFET in the circuit as the core. JFET circuit operation is the first (Q1) is the cable as a Hartley oscillator frequency modulated by the audio tone. The second (Q2) JFET is wired as a buffer to isolate the oscillator from the antenna based on the Q1. Diode D1 is used as varactor here.

The diode is reverse bias voltage generated by slim on pin 2 & 6 of IC1 results. This change in capacitance of the junction diode reverse bias, which in turn change the frequency of the oscillator to achieve frequency modulation. For inductor L1 can be made by winding 5 turns of 18 SWG enameled copper wire on 3 / 8 inches long, 3 / 16 inch diameter plastic tube. The coil must be tapped in the center. The antenna can be a 20cm long wire.

Car Anti-Theft Wireless Alarm

This alarm circuit is an anti- theft wireless alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF FM radio-controlled, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park. The receiver unit of the wireless alarm uses an CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside. Receiver is tuned to the transmitter’s frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transis- tor T2 (BC548) does not conduct. This results in the relay driver transistor T3 getting its forward base bias via 10k resistor R5 and the relay gets energised. The following is a schematic drawing:

When an intruder tries to drive the car and takes it a few metres away from the car porch, the radio link betw- een the car (transmitter) and alarm (receiver) is broken. As a result FM radio module gene-rates hissing noise. Hissing AC signals are coupled to relay switching circ- uit via audio transformer. These AC signals are rectified and filtered by diode D1 and capacitor C8, and the resulting positive DC voltage provides a forward bias to transistor T2. Thus transistor T2 conducts, and it pulls the base of relay driver transistor T3 to ground level. The relay thus gets de-activated and the alarm connected via N/C contacts of relay is switched on.

If, by chance, the intruder finds out about the wireless alarm and disconnects the transmitter from battery, still remote alarm remains activated because in the absence of signal, the receiver continues to produce hissing noise at its output. So the burglar alarm is fool-proof and highly reliable. (Ed: You may have some problem catching the thief, though, if he decides to run away with your vehicle_in spite of the alarm!)

Voltmeter To Frequency Meter Using 4528

Normally we often encountered the frequency meter can be used in speed sensor, tachometer, measurement or signal recurring. This frequency to voltage converter (FVC) can be used to change the voltage into a digital or analog tachometer. Circuit that consists of three blocks. The first block is squarer, the input signal to a square wave. This block is protected from high input voltage up to 400V, but remember this only works if the value of capacitor C1 is for 400V. Input Impedance around 560k, so it is safe to connect the ignition pick-up coil in parallel with the CDI (capacitor discharge ignition) circuits without a problem. Supply is protected from voltage spike by Zener diode D3. Here is a schematic picture:

The second block is retriggerable monostable multi vibrator. Monostable multi-vibrator is to convert fixed width pulses to provide output, the voltage output of the average will depend on the duty factor pulses input / waveform, but only depends on the input frequency. Pulse width is determined by R9 + R5 and C4. According to the datasheet of IC 4528, the period of the monostable :

t = 0.2 x R5 x C4 x ln (VDD-VSS)

R and C are in ohm and Farad, VDD-VSS is in the pin 16 voltage minus the voltage on pin 8, and t in seconds. Minimal value of R9, the monostable multi-vibrator output pulse width will be 0.2 * 4700 * 22e-9 * ln (12) = 5.139e-5, and this will change the frequency of 19.460 kHz to 12 Volt output. This gives a conversion factor 1.622kHz/Volt. If you set the maximum value to R9 (100k) then the pulse width of monostable multi-vibrator output akan 1.145 MS. This setting will give the maximum voltage output of 12V at 874Hz, or about 72.8Hz per Volt conversion. If you use the tachometer to the application, wide rage this adjustment will accommodate almost any type of engine.

A last block of the first order low pass filter about U2, about 0.1 seconds of time set by R6 and C5 constant. With the slow time, you can not read all the frequencies below 10Hz or close, but OK for a variety of applications. Although the diagram does not show the scheme decoupling capacitor for bypassing the supply line for u3 noise, it’s good to add a 100nF cap u3 as close as possible to the power pin (pin 8 and 16), since the monostable multi-vibrator is sensitive to such noise.

2-25V 5A Power Supply Using LM338

This circuit is a circuit diagram power supply circuit uses a LM338 adjustable 3 terminal regulator to supply a current of up to 5A over a variable output voltage of 2V to 25V DC. It will come in handy to power up many electronic circuits when you are assembling or building any electronic devices. The schematic and parts list are designed for a power supply input of 240VAC. Change the ratings of the components if 110V AC power supply input is required. The mains input is applied to the circuit through fuse F1. The fuse will blow if a current greater than 8A is applied to the system. Varistor V1 is used to clamp down any surge of voltage from the mains to protect the components from breakdown. Transformer T1 is used to step down the incoming voltage to 24V AC where it is rectified by the four diodes D1, D2, D3 and D4. Electrolytic capacitor E1 is used to smoothen the ripple of the rectified DC voltage.

Diodes D5 and D6 are used as a protection devices to prevent capacitors E2 and E3 from discharging through low current points into the regulator. Capacitor C1 is used to bypass high frequency component from the circuit. Ensure that a large heat sink is mounted to LM338 to transfer the heat generated to the atmosphere.

Toggle Flip Flop Laser Pointer Using CD4013

The circuit below is similar to the one above but can be used with a laser pointer to toggle the relay rather than a push button. The IR photo transistor Q1 (Radio Shack 276-145A) or similar is connected to the set input (pin 6). The photo transistor should be shielded from direct light so that the voltage at the set input (pin 6) is less than 1 volt under ambient conditions and moves to more than 10 volts when illuminated by the laser pointer or other light source.

The reset time is about a half second using a 4.7uF cap which prevents the circuit from toggling more than once during a half second interval. The 10K resistor and diode provide a faster discharge path for the 4.7uF cap so the circuit can be retoggled in less than 1 second. The 3K resistor in series with the photo transistor may need be adjusted for best performance. The relay shown is a solid state variety to be used with lights or other resistive loads at less than 3 amps. A mechanical relay can also be used as shown in circuit above.

Mobile Cellphone Battery Charger Circuit Using 555

This diagram is a series of circuits Mobile Cellphone Battery Charger. Stops charging when battery is full charged, Portable unit Charging of the mobile phone, cellphone battery is a big problem while traveling as power supply source is not generally accessible. If you keep your cellphone switched on continuously, its battery will go flat within five to six hours, making the cellphone useless. A fully charged battery becomes necessary especially when your distance from the nearest relay station increases. Here’s a simple charger that replenishes the cellphone battery within two to three hours. Basically, the charger is a current-limited voltage source. Generally, cellphone battery packs require 3.6-6V DC and 180-200mA current for charging. These usually contain three NiCd cells, each having 1.2V rating. Current of 100mA is sufficient for charging the cellphone battery at a slow rate. A 12V battery containing eight pen cells gives sufficient current (1.8A) to charge the battery connected across the output terminals. The circuit also monitors the voltage level of the battery. It automatically cuts off the charging process when its output terminal voltage increases above the predetermined voltage level. The following is a schematic drawing:

Part :

P1 = 20K
P2 = 20K
R1 = 390R
R2 = 680R
R3 = 39R-1W
R4 = 27K
R5 = 47K
R6 = 3.3K
R7 = 100R-1W
C1 = 4.7uF-25V
C2 = 0.01uF
C3 = 0.001uF
D1 = 5.6V-1W Zener
D2 = 3mm. Red LED
Q1 = SL100
S1 = On/Off Switch
B1 = 1.5vx8 AA Cells in Series
IC1 = NE555 Timer IC

Timer IC NE555 is used to charge and monitor the voltage level in the battery. Control voltage pin 5 of IC1 is provided with a reference voltage of 5.6V by zener diode D1. Threshold pin 6 is supplied with a voltage set by P1 and trigger pin 2 is supplied with a voltage set by P2. When the discharged cellphone battery is connected to the circuit, the voltage given to trigger pin 2 of IC1 is below 1/3Vcc and hence the flip-flop in the IC is switched on to take output pin 3 high. When the battery is fully charged, the output terminal voltage increases the voltage at pin 2 of IC1 above the trigger point threshold.

This switches off the flip-flop and the output goes low to terminate the charging process. Threshold pin 6 of IC1 is referenced at 2/3Vcc set by P1. Transistor Q1 is used to enhance the charging current. Value of R3 is critical in providing the required current for charging. With the given value of 39-ohm the charging current is around 180 mA. The circuit can be constructed on a small general-purpose PCB. For calibration of cut-off voltage level, use a variable DC power source. Connect the output terminals of the circuit to the variable power supply set at 7V. Adjust P1 in the middle position and slowly adjust P2 until LED (D2) goes off, indicating low output. LED should turn on when the voltage of the variable power supply reduces below 5V. Enclose the circuit in a small plastic case and use suitable connector for connecting to the cellphone battery.

20 watt Car Power Amplifier using TDA2004

This circuit diagram we Power Amplifier IC TDA2004. Main features of this powerful package MULTIWATT ® (a trademark of SGS-THOMSON Microelectronics), where an IC chip power amplifier is designed specifically for car radio applications, is the ability of high current (3.5A) and the ability to drive a very low Impedance (down to 1.6R). TDA2004 low noise, low distortion, and strong. Sense of security operations supported by the protection features: highly inductive load, the load dump voltage surge, too hot, AC-ground output short, fortuitous open ground. Here is a schematic diagram of a standard circuit:

This is another important cost and storage space: a very low external component count, and very simple mounting system with no need for electrical isolation between the package and heat sink because the heat from the metal contacts of the package are connected to land.

Simple Parking Sensor Using LM324

Circuit diagram is a simple parking sensors, sensing the distance between where the rear bumper of the car and obstacles behind the car. In the circuit diagram there are two parts to the scheme and the scheme for the transmitter receiver. Distance can be understood from a combination of LEDs (D5 to D7) glowing. At 25cm D7 akan beam, 20 cm in e6 & D7 akan shining and 5cm in the D7, D5 and e6 akan glow. When the constraints that exceed 25 cm above none of the LEDs will glow. This circuit is based on the LM324 as a core system. following is a circuit diagram for the image transmitter:

 

There are pictures on the IC1 NE555 is the cable as astable multivibrator increase IR diode D1 to emit IR pulses. That operates at a frequency transmitter must be set 120Hz.The IR pulses transmitted by D1 will be reflected on the obstacles and received by D2 (infra red). You can also use the photo diode. The received signal amplified by akan IC2a.The peak amplified signal is detected by diode D4 and capacitor C4.R5 and R6 compensates the forward voltage drop of D4.The output voltage from the peak detector will be proportional to the distance between the bumper cars and obstacles. Output from the peak detector is given to the input from three other comparators IC2b, IC2c and IC2d the IC2 LM324. The comparators switch status LEDs according to their input voltage inverting input and the reference voltage at the non-inverting input. Resistances R7 to R10 is used to set the reference voltage for the comparators. Here is a circuit diagram for the image of the recipient:

To note that the D1 & D2 must be installed near (~ 2cm) of each other, seen in the same direction. D1 which can be a general purpose IR LED. D2 which can be general purpose IR photo diode with filter Sunday. Right to work in the circuit, some trial and error is required with the position of D1 and D2 in the dash board. All capacitors must be rated 25V.

18W Amplifier Circuit Using HA13118

This is a circuit diagram of power amplifier circuit. Circuit diagram of this amplifier is a type of mini amplifier, which generated power is only 18W. Circuit diagram audio amplifier IC HA13118 supported by the component. The main types of this amplifier is the amplifier bridge as the output line is not grounded. Supply voltage required for this circuit is 8 – 18V DC, at least 1-2 Amps. Maximum output power will only be obtained with a 18V power supply at greater than 2 A, using 4 ohm speakers. The following is a schematic drawing:

Power supply must be filtered well to reduce the main hum, which regulated the supply will further reduce noise. Additional filtering is unnecessary if operating from a battery supply. This power amplifer circuit despite having a low power, but the results are quite satisfactory. Power amplifer is suitable to use in car audio systems.

2 X 22 Watt Stereo Amplifier

2 X 22 Watt Stereo Amplifier using IC TDA 1554

Here is the circuit diagram of a powerful and high quality stereo amplifier using IC TDA 1554.The circuit has only very few components.The circuit works best with a 4 Ohm speaker.



Notes

IC must be connected to a heat sink. A computer cabinet fan can also be used in addition(not necessary).Any way better the cooling better the performance.The circuit roughly draws 6A current at 12 V at full volume.So the power supply must be any thing more than 6A.Up to 18 V can be used ,which gives a bit more power boost.Commonly used is 12 V.



Parts List

R1 39K 1/4 Watt Resistor

C1,C2 10uf 25V Electrolytic Capacitor

C3 100uf 25V Electrolytic Capacitor

C4 47uf 25V Electrolytic Capacitor

C5 0.1uf 25V Ceramic Capacitor

C6 2200uf 25V Electrolytic Capacitor

U1 TDA1554 Two Channel Audio Amp Chip

MIS Heatsink For U1, Binding Posts (For Output), RCA Jacks (For Input)



Circuit Diagram .

FM Transmitter

2 km FM transmitter

With a matching antenna, the FM transmitter circuit shown here can transmit signals up to a range of 2 kilo meters. The transistor Q1 and Q2 forms a classic high sensitive preamplifier stage. The audio signal to be transmitted is coupled to the base of Q1 through capacitor C2. R1, R3, R4, R6, R5 and R9 are the biasing resistors for the preamplifier stage comprising of Q1 and Q2. Transistor Q3 performs the collective job of oscillator, mixer and final power amplifier.C9 and L1 forms the tank circuit which is essential for creating oscillations. Inductor L2 couples the FM signal to the antenna.

Circuit diagram.

Notes.

■Assemble the circuit on a good quality PCB.

■The circuit can be powered from anything between 9 to 24V DC.

■Inductor L3 can be a VK220J type RFC.

■For L1 make 3 turns of 1mm enamelled copper wire on a 10mm diameter plastic former. On the same core make 2 turns of 1 mm enamelled copper wire close to L3 and that will be L2.

■Frequency can be adjusted by varying C9.

■R9 can be used to adjust the gain.

■For optimum performance, value of C8 must be also adjusted.

■Using a battery for powering the circuit will reduce noise.

Electronic Combination Lock

Simple Electronic Combination Lock using IC LS 7220


This is the circuit diagram of a simple electronic combination lock using IC LS 7220.This circuit can be used to activate a relay for controlling (on & off) any device when a preset combination of 4 digits are pressed.The circuit can be operated from 5V to 12V.

To set the combination connect the appropriate switches to pin 3,4,5 and 6 of the IC through the header.As an example if S1 is connected to pin 3, S2 to pin 4 , S3 to pin 5, S4 to pin 6 of the IC ,the combination will be 1234.This way we can create any 4 digit combinations.Then connect the rest of the switches to pin 2 of IC.This will cause the IC to reset if any invalid key is pressed , and entire key code has to be re entered.

When the correct key combination is pressed the out put ( relay) will be activated for a preset time determined by the capacitor C1.Here it is set to be 6S.Increase C1 to increase on time.

For the key pad, arrange switches in a 3X4 matrix on a PCB.Write the digits on the keys using a marker.Instead of using numbers I wrote some symbols!.The bad guys will be more confused by this.

 

  

Parts List

C1 1 1uF 25V Electrolytic Capacitor

C2 1 220uF 25V Electrolytic Capacitor

R1 1 2.2K 1/4W Resistor

Q1 1 2N3904 NPN Transistor 2N2222

D1 1 1N4148 Rectifier Diode 1N4001-1N4007

K1 1 12V SPDT Relay Any appropriate relay with 12V coil

U1 1 LS7220 Digital Lock IC

S1-S12 12 SPST Momentary Pushbutton Keypad (see notes)

HD1 1 12 Position Header

Simple Code Lock circuit

This is Simple Code Lock circuit. This circuit will turn on a relay when the 8-way DIP switches receives the correct code. Here is the schematic diagram of the circuit:

There are two different types of DIP, they are piano-key DIP sw and 8-way DIP sw. This circuit will not draw the current if the switch is kept off. This circuit can give 256 different combination because the combination is in binary. So it would be very difficult for a burglar to keep up with the settings of the switches

Intercom

Below is a 2-station intercom using common 8R mini speakers. The “press-to-talk” switches should have a spring-return so the intercom can never be left ON.

Power the speaker from a separate power supply is the secret to preventing instability (motor-boating) with a high gain circuit like this. An extra station (or two extra stations ) can be connected to this design.