AUM001
Audio
Stereo audio power amplifier
A compact stereo amplifier for experimenting with speaker-level audio from a 12 V supply.
Original schematic↗
The circuit library.
Find a signal worth following. Original schematics, clearer explanations, and practical notes for your next experiment.
AUM002
Audio
Electret microphone preamplifier
Bring a small microphone signal up to a useful level with an adjustable LM358 preamplifier.
Original schematic↗
AUM003
Audio
Bass-boost audio amplifier
Explore low-frequency emphasis with a small mono speaker amplifier.
Original schematic↗
AUM004
Audio
LM380 two-way intercom
Use a loudspeaker as both a sound pickup and an output transducer in a wired intercom.
Original schematic↗
AUM005
Audio
Three-output audio distribution amplifier
Buffer one audio source and feed three separate line-level connections.
Original schematic↗
AUM006
Audio
Baxandall bass and treble control
Shape an audio signal with a passive tone network and two transistor stages.
Original schematic↗
AUM007
Audio
Loudspeaker microphone preamplifier
Turn a small dynamic loudspeaker into a practical speech pickup.
Original schematic↗
AUM008
Audio
Ten-band active audio equalizer
Study a bank of active filters for adjusting different parts of the audio spectrum.
Original schematic↗
AUM009
Audio
Single-supply stereo tone control
Adjust volume, balance, bass, and treble with a compact stereo control stage.
Original schematic↗
AUM010
Audio
TDA2030 audio amplifier
Build a class-AB mono amplifier around the classic TDA2030.
Original schematic↗
AUM011
Audio
20 W audio power amplifier
A speaker amplifier design with an output network intended for higher current.
Original schematic↗
AUM012
Audio
Stereo matrix surround decoder
Derive additional audio channels from the relationship between left and right signals.
Original schematic↗
AUM013
Audio
Two-input audio mixer
Combine two audio sources with individual level and balance controls.
Original schematic↗
AUM014
Audio
250 mW audio amplifier
A small speaker amplifier illustrating an alternative bias and feedback arrangement.
Original schematic↗
AUM015
Audio
Push-button stereo volume control
Set a stereo audio level in steps using a PT2253 and LM358 buffers.
Original schematic↗
CHI001
Converters & charging
Transformer inverter study
An archived push-pull inverter for studying DC-to-AC conversion.
Review required↗
CHI002
Converters & charging
Two-cell Ni-Cd charger study
Examine a comparator-based charge cutoff for two small nickel-cadmium cells.
Review required↗
MSR001
Test & measurement
ICL7107 digital voltmeter
Display a measured voltage with a 3½-digit LED converter.
Original schematic↗
MSR002
Test & measurement
Diode temperature display
Use the temperature dependence of a silicon diode in a digital thermometer.
Original schematic↗
MSR003
Test & measurement
LM3914 battery voltage monitor
See a battery’s terminal voltage on a ten-LED display.
Original schematic↗
MSR004
Test & measurement
Crystal oscillator tester
Check whether a crystal oscillates in a simple transistor test circuit.
Original schematic↗
MSR005
Test & measurement
PIC VHF/UHF frequency counter
Count high-frequency signals using an RF prescaler and a PIC16F84.
Original schematic↗
MSR006
Test & measurement
Digital frequency comparator
Compare two pulse frequencies using flip-flops, a NAND gate, and an LM311.
Original schematic↗
MSR007
Test & measurement
Electronic metronome
Generate a repeating beat for practicing rhythm and exploring oscillator timing.
Original schematic↗
MSR008
Test & measurement
AD8313 RF signal-strength meter
Turn an RF detector’s output into a ten-step visual indication.
Original schematic↗
PCR001
Computer interfaces
Parallel-port LCD interface
Drive a 16×2 character display from a legacy PC printer port.
Original schematic↗
PCR002
Computer interfaces
PL2303 USB-to-RS-232 interface
Study a USB serial adapter based on the Prolific PL2303 family.
Original schematic↗
POS001
Power supplies
Inductor-based DC step-up converter
Explore how a switched inductor can produce a higher DC voltage.
Original schematic↗
POS002
Power supplies
12 V to 6 V linear regulator
Reduce a nominal 12 V supply for a lower-voltage DC load.
Original schematic↗
POS003
Power supplies
LM723 adjustable bench supply
Explore adjustable voltage and current limiting with a classic regulator.
Review required↗
RFR001
Radio & RF
Class-C RF power amplifier
Study a tuned transistor output stage for a radio transmitter.
Original schematic↗
RFR002
Radio & RF
Two-transistor FM transmitter
Explore microphone amplification and frequency modulation with two 2N2222 transistors.
Original schematic↗
RFR003
Radio & RF
Analog television A/V modulator
Combine composite video and an audio subcarrier in a historic VHF design.
Original schematic↗
RFR004
Radio & RF
Buffered crystal oscillator
Generate a crystal-controlled signal and isolate it from the load.
Original schematic↗
RFR005
Radio & RF
Crystal-based video RF modulator
Convert a composite video signal into a historic VHF television channel.
Original schematic↗
RFR006
Radio & RF
Logic-gate FM oscillator
An experimental FM source built around inverters and a 10.7 MHz resonator.
Original schematic↗
RFR007
Radio & RF
Video-only television modulator
A tunable analog RF modulator for composite camera signals.
Original schematic↗
RFR008
Radio & RF
Three-stage FM transmitter
Study separate audio, RF oscillator, and RF output stages.
Original schematic↗
RFR009
Radio & RF
Two-stage UHF antenna preamplifier
Add gain ahead of a receiver with a filtered, two-stage RF amplifier.
Original schematic↗
RFR010
Radio & RF
BF180 UHF antenna preamplifier
A tuned RF input and common-base transistor stage for receiver experiments.
Original schematic↗
RFR011
Radio & RF
TCA440 27 MHz AM receiver
Follow a superheterodyne signal path from RF input to detected audio.
Original schematic↗
RFR012
Radio & RF
FM multiplex stereo decoder
Recover left and right audio from a compatible FM multiplex signal.
Original schematic↗
RFR013
Radio & RF
Analog satellite receiver study
An archival tuner, video detector, and audio decoder for analog satellite signals.
Original schematic↗
RFR014
Radio & RF
SAB6456 divide-by-64 prescaler
Reduce an RF frequency to a lower rate for counting or comparison.
Original schematic↗
RFR015
Radio & RF
20 m variable crystal oscillator
Explore the tuning-range and stability tradeoff of a buffered VXO.
Original schematic↗
SEC001
Security & sensing
Capacitive proximity alarm
Detect a nearby hand by disturbing a sensitive RC oscillator.
Original schematic↗
SEC002
Security & sensing
Infrared remote-control relay
Send a light signal to a separate receiver that operates a relay.
Original schematic↗
SEC003
Security & sensing
Four-step electronic combination lock
Demonstrate sequential switching with a simple resettable lock circuit.
Original schematic↗
SEC004
Security & sensing
Dual-555 door alarm
Use two timer stages to provide an exit delay and a door-triggered alarm.
Original schematic↗
TEL001
Telephony
Analog telephone speech interface
Study the speech path of a traditional wired telephone.
Original schematic↗
TEL002
Telephony
Telephone-triggered light controller
Detect ringing and off-hook conditions to control a timed light output.
Review required↗
TEL003
Telephony
DTMF tone decoder
Convert telephone-style dual-tone signals into a digital code.
Original schematic↗
UCT001
Microcontrollers
PIC hobby-servo controller
Adjust a small servo’s position using a switch and pulse-width control.
Original schematic↗
VID001
Video
CA3100 video distribution amplifier
Buffer a composite video signal for distribution to following equipment.
Original schematic↗
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