LM324Analog
Photodiode amplifier
How a transimpedance amplifier built with an LM324 and a feedback resistor converts photodiode current into a voltage proportional to the received light intensity.
openschematics.cc
Application examples for hardware design
HX711Analog
Load cell front-end with 24-bit ADC
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.