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MM74C922N-based encoded matrix keypad

Posted on May 17, 2014 by R-B 5 comments

Matrix keypads are an excellent way of providing user input data into microcontroller-based systems. Keypads find applications in remote controls, standalone data-loggers, security systems, door entry systems, calculators, microwave ovens, etc. They are usually implemented as pushbutton switches arranged in a row and column matrix format to reduce the number of I/O connections. For example, a 16-switch keypad is arranged in a 4 X 4 matrix format requiring 8 I/O connections. A pressed key is detected and identified by scanning the keypad to look for a short circuit condition between a row and a column wire. The keypad scanning can

RFID access control for garage door

Posted on May 14, 2014 by R-B Leave a comment

Jason Hamilton has built this Arduino-based RFID access control to open his garage door using RFID. The project has a master RFID key hard-coded into the Arduino firmware, which allows you to add other keys to the system. The new keys are all stored into the EEPROM memory of Arduino.

Single and multi-phase AC induction motor control using the PIC16F1509 microcontroller

Posted on May 13, 2014 by R-B One comment

This application note from Microchip provides a detailed analysis of driving a single and multi-phase AC induction motor using the 8-bit PIC microcontrollers. It shows how to build a low-cost three-phase inverter circuit using PIC16F1509 to add speed control and soft-start to a single and multi-phase AC induction motor.

DC booster for your 12V load

Posted on May 13, 2014 by R-B One comment

This 12V DC booster circuit uses the MC34063A device which contains all the primary functions required for DC−to−DC converters. It has a built-in temperature compensated reference, comparator, controlled duty cycle oscillator with an active current limit circuit, driver and high current output switch. It operates from 3.0 to 40.0V DC and can supply output current up to 1.5A. This booster can thus power your 12V load with a 3.7V Li-Ion battery.

DIY lock-in amplifier using the AD630 balanced modulator

Posted on May 13, 2014 by R-B One comment

Lock-in amplifiers are used to detect and measure very small AC signals which are buried in an overwhelming noise. For example, consider a case where you want to single out a 5 mV sine wave from a white noise signal with 2 V amplitude. A lock-in amplifier makes this measurement possible. It uses a technique called phase-sensitive detection, which uses a specific frequency reference to extract the component of the signal at the reference frequency and phase. Noise signals, at frequencies other than the reference frequency, are then rejected and do not affect the measurement. This instructable describes how to construct

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