VISIBLE_LIGHT_RECEIVER

Published:2009/6/17 1:41:00 Author:May

This receiver for amplitude-modulated light signals uses phototransistor Q1 mounted in a para-bolic reflector (to increase range). Any npn phototransistor should work. Emitter-follower Q2 drives amplifier Q3. The output from Q3 feeds volume control R7 and audio amplifier UI. A 9- to 12-V supply is recommended for the receiver.   (View)

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LIGHT_WAVE_VOICE_COMMUNICATION_RECEIVER

Published:2009/6/16 23:54:00 Author:May

This light-wave receiver consists of a 741 op-erated as a preamplifier and an LM386 operated as a power amplifier. Potentiometer R2 is the gain control. Various kinds of detectors can be used as the front end of the receiver. Phototransistors are very sensitive, but they do not work well in the presence of too much ambient light. A 100-kQ se-ries resistor is required if you use a phototransis-tor. Solar cells, photodiodes, and LEDs of the same semiconductor as the transmitter all work well in this circuit.   (View)

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FM_LIGHT_BEAM_RECEIVER

Published:2009/6/16 23:51:00 Author:May

This receiver will pick up IR or light beams that are frequency modulated on a 50-kHz carrier Q2/Q1/Q3/Q4 from an active filter and amplifier and differential amp Q5/Q6 provide more gain.   (View)

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POWER_MOSFET_INVERTER

Published:2009/6/16 23:29:00 Author:May

T1 is a suitable transformer for the voltage desired, with a 12.6-V CT winding.   (View)

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dc_to_ac_INVERTER

Published:2009/6/16 23:28:00 Author:May

A multivibrator circuit drives a pair of 2N3055 power transistors transformer with a 120-V primary.   (View)

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DIGITAL_INVERTER

Published:2009/6/16 23:27:00 Author:May

A CMOS digital inverter is formed by con-necting two MOSFETS, as shown.   (View)

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ONE_WAY_VOICE_ACTIVATED_INTERCOM

Published:2009/6/16 22:57:00 Author:May

An omnidirectional electret microphone can be used to pick up the sound and convert it into an electrical signal. The output of the microphone is fed along two paths. In the first path, the signal is sent to the inverting input at pin 6. In the second path, the microphone signal is fed to the non-in-verting input of U2, where it is amplified and output to the speaker, SPKR1.   (View)

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FAST_INTEGRATOR

Published:2009/6/16 22:54:00 Author:May

  (View)

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IR_RECEIVER

Published:2009/6/16 22:26:00 Author:May

This circuitis just about the simplest IR ro-celver you can build The parts are cheap，the lay－outis not critical，and a 9-V battery will last a longtime   (View)

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WIRELESS_IR_HEADPHONE_RECEIVER

Published:2009/6/16 22:18:00 Author:May

IR detector diode D1 intercepts the IR signal at around 40 kHz and feeds it from U1, a high-gain preamp, to PLL, U2, a 4046 configured to serve as an FM detector. U3 is an audio amplifier that feeds a pair of headphones or a speaker.   (View)

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WIRELESS_IR_HEADPHONE_TRANSMITTER

Published:2009/6/16 22:17:00 Author:May

The transmitter for the wireless headphones is built around a CD4046 CMOS phase-locked loop, coupled with a driver transistor, and a pair of infrared LEDs. Although the CD4046 is comprised of two phase comparators, a voltage-controlled oscillator (or VCO), a source follower, and a zener ref-erence, only its VC0 is used in this application.   (View)

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INFRARED_RECEIVER

Published:2009/6/16 22:14:00 Author:May

The circuit operates from a 5-V supply and has a current consumption of 2 mA. The output is a current source that drives or suppresses a current of more than 75 pA with a voltage swing of 4.5 V.The Q-killer circuit eliminates distortion of the output pulses because of the decay of the tuned in-put circuit at high input voltages. The input circuit is protected against signals of more than 600 mV by an input limiter. The typical input is an AM signal at a frequency of 36 kHz.   (View)

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AND_GATE

Published:2009/6/16 21:46:00 Author:May

A left-over section of a quad op amp can be used to save cost and eliminate an extra logic chip for this AND gate.   (View)

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1_kHz_TONE_FILTER

Published:2009/6/16 21:29:00 Author:May

The Wien-bridge based filter has a variable bandwidth and a center frequency of 900 Hz. The circuit will oscillate if the 10-kΩ pot is set too low.   (View)

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FULL_WAVE_RECTIFIER_AVERAGING_FILTER

Published:2009/6/16 21:27:00 Author:May

The input signal is rectified by D1 and D2 Op amp U1-a，and fed to output amp U2 R8 is set for correct circuit calibration.   (View)

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PASSIVE_T_FILTER_CONFIGURATIONS

Published:2009/6/16 21:19:00 Author:May

  (View)

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BI_QUAD_RC_BANDPASS_FILTER

Published:2009/6/16 21:19:00 Author:May

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AUDIO_RANGE_FILTER

Published:2009/6/16 21:18:00 Author:May

The LMF380 switched audio filter by National Semiconductor is used here to obtain a third-oc-tave filter set that covers the entire audio range.   (View)

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455_kHz_NARROW_BAND_IF_FILTER

Published:2009/6/16 21:14:00 Author:May

This filter uses five 455-kHz ceramic resonators. The impedance is 330Ω, the bandwidth is 800 Hz, and the ultimate rejection ≥60dB. The ceramic resonators could be replaced by crystals.   (View)

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CURRENT_DRIVEN_SALLEN_KEY_FILTER

Published:2009/6/16 21:13:00 Author:May

The low-pass Sallen-Key filter is staple for designers because it contains few components (A).By redesigning the filter, a current to voltage conversion can be avoided when the input signal to be filtered is in current form (B).   (View)

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