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555 Contest Entry: AM radio

Posted on February 26, 2011 by R-B Leave a comment

555 timer based AM radio receiver published on Tube Time is one of many entries for the currently running 555 contest. This project uses a 555 timer as AM demodulator plus amplifier to drive the speaker. The radio signal is tuned with an LC tank circuit. The 555 timer is configured as a PWM where a ramp signal is created with a capacitor and a potentiometer. The radio signal picked by the LC circuit is superimposed on the ramp signal which varies the duty cycle of the output PWM wave. The variation in the duty cycle corresponds to the audio

2-Wire Keypad Interface Using a 555 Timer

Posted on February 20, 2011 by R-B 23 comments

Keypads are a very commonly used input device in microcontroller-based systems. In a keypad, multiple switches are arranged in rows and columns so that they could be interfaced to a microcontroller with a minimum number of I/O pins. For example, a 12-key keypad is arranged in a 4×3 format, which allows to interface the 12 keys to a microcontroller with only 7 connections. The location of each key on the keypad is defined by two coordinates: the row and the column. When a key is pressed, it connects its row with its column. The microcontroller must scan all the rows

Radio frequency identification (RFID) with a microcontroller

Posted on February 18, 2011 by R-B Leave a comment

RFID is a technology that uses radio waves for transmitting the identity (unique serial number) of an object or a person. If you have an electronic key to access your office building, it probably uses the same technology. An RFID system has a reader and a transponder (also called tag). The reader transmits electromagnectic waves in its surrounding through an antenna system, and when a tag passes passes through the zone, it is activated and the reader can read the identification data stored inside the electronic tag.

How to measure capacitance with a microcontroller?

Posted on February 15, 2011 by R-B 2 comments

Microcontrollers are widely used in measuring various physical variables. The techniques involved in the measurements could be different for individual variable type and are mostly based on the characteristics of the variables to be measured. This tutorial describes some methods for measuring the capacitance of a capacitor using microcontrollers. The techniques use the characteristics of the capacitor itself and are therefore universal and can be easily implemented with any microcontrollers.

Where do I buy my electronics components from?

Posted on February 14, 2011 by R-B 4 comments

I have been living in Southern Virginia for past 3 years and I haven’t seen any retail store to shop for electronics components that are needed for my projects, except the Radioshack stores. I don’t prefer to go to Radioshack as the prices are much higher than my budget. A few years ago, I discovered an online store named Futurlec. I was surprised with their prices, their stuffs were really cheap and of good quality. I made 4 orders in the first year, and I was very happy with what I got. The only problem was they shipped their items

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