Miyerkules, Hulyo 8, 2015

1 Watt FM Amplifier Circuit

This is a 1 watt fm amplifier with a good design that can be used to amplify a rf signal in the 88 – 108 MHz band. It is very sensitive if you use good rf power amplifier transistors, trimmers and coils. It has a power amplification factor of 9 to 12 dB (9 to 15 times). At an input power of 0.1W the output will be 1W.

You must choose T1 depending on applied voltage. If you have a 12V power supply then use transistors like: 2N4427, KT920A, KT934A, KT904, BLX65, 2SC1970, BLY87. At 18 to 24V power supply you must use transistors like: 2N3866, 2N3553, KT922A, BLY91, BLX92A. You may use 2N2219 at 12V but you will get an output power of 0.4W maximum.

Calibration of the 1 watt fm power amp

Do not connect any RF source, just apply the power supply and measure the voltage at point 1. Adjust R3 until you measure 0.7V. Replace the antenna with 2 x 100 Ω 0.5W resistors in parallel at the RF output. Now connect the rf signal that you need to amplify and connect this RF Probe to the output.
Slowly adjust C1 in order to get the highest voltage value on the rf probe. Now adjust R3 again to get 0.7 V at point 1. Now adjust C5 and C6 for maximum output voltage (must be between 12V to 18V).

Check the temperature of T1′s heatsink, if it is ok turn off the power supply, disconnect the 2 resistors of 100 Ω and connect the antenna (keep the probe connected). Apply the power and now adjust again C1, C5 and C6 for maximum voltage indication on the probe.

You may use an ampermeter in order to check the current flow through T1. This must not exceed 150mA at 12V and 100mA at 24V or the transistor will burn. L2 and L3 coils must have an angle of 90 degrees between them. Don’t use the 1W rf fm amplifier if you find that you tv set is jammed and the laws of your country does not allow the use of FM transmitters.

Component values
R1 = 100Ω
R2 = 2.2KΩ at 12V and 4.7kΩ at 24V
R3 = 10KΩ
R4 = 100Ω
C1 = C5 = C6 = 10 – 60pF
C2 = C4 = 1nF
C3 = 10uF
D1 = 1N4148
L1 = 20 turns of 0.2mm EnCo* wire over R4
L2 = 7 turns of 0.8mm EnCo* wire with 6mm diameter on air
L3 = 4 turns of 0.8mm EnCo* wire with 7mm diameter on air
T1 = 2N4427, KT920A, KT934A, KT904, BLX65, 2SC1970, BLY87 (2N2219, output of 0.4W) at 12V
T1 = 2N3866, 2N3553, KT922A, BLY91, BLX92A at 24V
* EnCo = enamelled copper

Alternating Current(AC) Detector

AC to DC rectifier

smoothing output

Simple Stereo Amplifier For any Mp3 Player

500 WATT RMS CLASS-AB AUDIO POWER AMPLIFIER FOR 2-OHMS LOUDSPEAKER

Infrared Headphones Receiver Circuit

Use this infrared headphones receiver with the ir headphones transmitter.
Use 600Ω headphones. BPW41N and BP104 have a filter for visible light and are centered on 950nm at 25⁰C.

At normal light illumination and 3 to 4 meters distance the audio distorsion were 1 – 2%, wich is not bad for such a simple ir headphones receiver schematic

IR headphone receiver circuit diagram

Infrared Headphones Transmitter Circuit

The transmitter offers a optical link (infrared) for headphones. Three infrared leds (ir) are polirised by T1 current, P1 is used to adjust the current level . Current consumption of this headphones infrared transmitter is about 60mA at 9V.

Maintain separated adapter ground and audio signal ground to prevent current reactions thru LED. The optical link is relative directional and can be improved by placing the leds in different angles and placing reflectors behind them.

The optimal input audio level is 100 – 200mV for 1.2 – 2.4 m coverage of this headphones ir transmitter. On the site we provide the infrared receiver schematic for this infrared headphones transmitter.

Infrared headphones transmitter circuit

Impulse Modulated Infrared Transmitter Circuit

This infrared transmitter can be used with this infrared receiver. This transmitter uses. The modulated signal is produced by comparison of an audio signal with a triangle signal of high frequency using a comparator IC. An appropriate triangle signal generator must have the offset equal with half of the 5V power supply voltage and the triangular signal size is 2.5V. Check out the infrared alarm circuit too.

For a wider range of the infrared transmitter the current through LEDs must he high. Because the LED cannot stand high dc currents, the impulses must be short so we use PWM. The pulses are generated by XOR gate IC2d that compares the original PWM signal with the delayed by R5-C3-IC2c. The IC2d output signal produce T1 switching and in this way the LEDs absorbed current is limited at 400 mA peak with help from R6. The average current consumption of the infrared transmitter circuit will be around 90 mA.

P3 adjustment is made without input signal with help of an oscilloscope, so that all impulses from the output signal have the same width. Then adjust P2 so that the intervals between impulses come equal. IC1 output will then be a perfect rectangular wave.

Working with the receiver and the transmitter at the same time feed an input signal at maximum value then adjust P1 to obtain minimum interference in the received signal. Finally, you may use IC2a and IC2b for the triangle signal generator.

Infrared Transmitter Circuit Diagram

Infrared Alarm Barrier Receiver Circuit Schematic

How to make an infrared barrier alarm

The transmitter and receiver circuits of the infrared alarm system shown here have been designed for a range of several meters, almost independent of ambient light conditions. Only in the rare case of the receiver sensor being exposed to bright, direct sunlight, some screening measures have to be added.

The transmitter does not emit a continuous infrared signal, Rather, it is modulated, that is, the 36-kHz carrier used to pulse the IRED (infrared emitting diode) on and off is itself switched on an off at a rate of about 300 Hz. The reason for doing so is that most infrared sensors, including the ones suggested in the diagram do not respond very well to continuous incidence of infrared light. Switching the IR source off, even for a small period, allows IR detectors to ‘recuperate’, and so optimise their ability to minimize the response to ambient light.

The transmitter consists of two oscillators built around the ubiquitous 555 IC. Here, the current-saving CMOS version TLC555 (or 7555) is used. Alternatively, the two 555’s may be replaced by a single TLC556 (or 7556). IC1 is the 300-Hz generator, IC2, the 36-kHz source. The IRED type LD274 is pulsed at a relatively high peak current via driver transistor T1. If in your application the distance covered by the IR beam is relatively short, the value of resistor R5 may be increased to save on current consumption. Preset P1 is adjusted for a carrier frequency of 36 kHz exactly (failing test equipment, adjust it for optimum range).

The receiver is equally simple and also based on a CMOS 555. As long as the sensor picks up infrared light from the transmitter, the reset input of the 555 IC is held low and the buzzer is silent. Components D1 and C2 act as a low-frequency rectifier to cancel the effect of the 300-Hz modulation on the transmitter signal. When the infrared light beam is interrupted, the oscillator built around the 555 is enabled and starts to produce a warning tone.

Finally, the test values indicated in the infrared barrier alarm circuit diagram are average dc levels measured with a DVM, under light/no light conditions. In fact, most test points carry rectangular or sawtooth waveforms.

Infrared Light Alarm Transmitter Circuit Schematic

This infrared alarm barrier can be used to detect persons passing through doorways, corridors and small gates. The transmitter emits a beam of infrared light which is invisible to the human eye. The buzzer at the output of the receiver is activated when the light beam is interrupted by a person passing through it.

Invisible Infrared Alarm Circuit

This circuit uses invisible infrared light to detect the movement of people through the door. A short beep will be generated when the infrared beam breaks. So it is ideal to monitor the passages in shops, banks etc where many people are moving.

Two Infrared LEDs always emit continuous infrared beam to the Photodiode. The IR LEDs and Photodiode are placed on the opposite frames of the door and properly aligned. Resistor R1 is the current limiter giving around 70 mA current through the LEDs which is necessary to increase the output of IRLEDs. IC1 is designed as Current to Voltage converter with the reverse biased photodiode connected to its inverting input. The non inverting input is directly grounded.

Resistor R2 and VR1 forms the feedback loop to adjust the sensitivity of the IC. Normally the Photodiode generates a small current by accepting the energy from the infrared Beam. This tiny current will be amplified by IC1 and gives a high output. This forward biases T1 and it conducts. The emitter current from T1 keeps T2 off since it is a PNP transistor. Since T2 is off, Buzzer remains silent. In short, in the standby mode, LED glows indicating the active state of circuit and buzzer remains off.