LM3914Analog
10-LED bar voltmeter
10-LED bar voltmeter built with the LM3914, a driver with ten internal comparators, a programmable reference and constant-current outputs that light the LEDs in bar mode across a 5 V full scale.
CD4026Digital
Single-digit counter with 7-segment display
CD4026 decade counter with a built-in driver for a common-cathode seven-segment display. One pushbutton advances the count from 0 to 9 and a second one clears it. No microcontroller and no external decoder — the chip does both jobs on its own.
AD8302RF
Gain and phase meter for RF signals
Gain and phase meter between two RF signals built around the AD8302, which compares amplitude and phase from DC up to 2.7 GHz and delivers two voltages — one proportional to the amplitude ratio in dB and one to the phase difference in degrees — directly readable by an ADC.
KA2284Audio
5-LED VU meter
5-LED VU meter built with the KA2284, a dedicated IC that rectifies an audio signal and distributes it across a bargraph of three green LEDs, one yellow and one red.
2N3906Analog
Dual LED blinker with PNP astable multivibrator
Astable multivibrator built with two 2N3906 PNP transistors that take turns driving the two anodes of a common-cathode bicolor LED, making it blink alternately between red and green.
CD4017Digital
Sequential 10-output counter with LEDs
CD4017 decade counter driven by hand with a pushbutton. Each press moves the active output to the next LED (D1 to D10), and a second button clears the count back to zero. A classic way to see CMOS logic in action without an oscilloscope.
2N3904Analog
Astable multivibrator with transistors
Classic astable multivibrator built with two 2N3904 transistors that switch alternately to blink two LEDs. The circuit generates a square wave with no integrated circuit at all.
LOC110Analog
Linear isolation amplifier for an isolated analog input
Isolation amplifier built around the LOC110 linear optocoupler that copies a 0 to 5 V analog voltage across a galvanic barrier. The trick is the servo loop on the input side, which cancels the LED non-linearity and leaves the gain set by nothing but two resistors.
LM2596Power
Step-down DC-DC converter 12 V to 5 V, 3 A
Step-down DC-DC converter built around the LM2596-5.0 that turns a 12 V input into a regulated 5 V output at 3 A. Using the fixed-voltage version of the IC shrinks the circuit to the bare minimum — an input capacitor, a Schottky freewheeling diode, an inductor and an output capacitor.
CH340GDigital
USB to UART converter
USB to asynchronous TTL serial port converter based on the WCH CH340G in SOP-16, with a 12 MHz crystal and bus-powered from USB.
INA1650Audio
Balanced line driver for XLR output
Balanced line driver for XLR output based on the Texas Instruments INA1650, with laser-trimmed matched internal resistors, integrated EMI/RFI filters and dual ±18 V supply.
OPA1678Audio
Phantom-powered piezoelectric microphone preamplifier
Differential preamplifier for a piezoelectric microphone powered by phantom power, with ESD protection and Zener clamping, using both channels of the OPA1678 as mirror branches.
HLW8032Sensors
AC power meter
How to measure the voltage, current and power consumed by a 220 V AC load using the HLW8032, a resistive divider and a 1 mΩ shunt resistor.
LM324Sensors
Photodiode light sensor
How a transimpedance amplifier built with an LM324 and a feedback resistor converts photodiode current into a voltage proportional to the received light intensity.
LM386Audio
Mono audio amplifier
How to build a low-power mono audio amplifier with the LM386, a gain capacitor and a coupling capacitor to drive a speaker directly from a 4 to 12 V supply.
HX711Sensors
Force/weight sensor
A concise guide to the HX711 from Avia Semiconductor — pinout, two-wire serial interface and internal regulator for connecting a load cell directly to a microcontroller.
CH9329Digital
USB keyboard and mouse emulator via serial port
A concise guide to the CH9329 from Nanjing Qinheng Microelectronics — pinout, operating modes and serial communication modes for emulating a USB keyboard, mouse and custom HID device.
TM1637Digital
LED display and keypad driver
A concise guide to the TM1637 from Titan Micro Electronics — pinout, internal operation and the two-wire communication protocol used to drive 7-segment displays and read a keypad matrix.
LM324Analog
Square wave oscillator
How a square wave oscillator works using an LM324 operational amplifier with positive feedback and a timing capacitor.
A4988Power
Stepper motor driver
How the A4988 application circuit works — the bipolar stepper motor driver with microstepping and PWM current regulation.
7805Power
High current regulator
How to get past the current limit of a 7805 regulator by adding a PNP pass transistor. Resistor Re, together with the MJ2955's VBE, sets when the transistor steps in to share the current, taking the output up to about 5 A.
7805Power
Constant current source
How to use a 7805 voltage regulator as a constant current source. A single resistor sets the output current at I = 5 V / R, taking advantage of the fixed 5 V the regulator keeps between its output and common pins.