This stepper motor driver can control two independent steppers via RS232 interface. Control commands can be sent by using simple terminal program like HyperTerminal. Circuit is capable to drive two unipolar stepper motors operating in full step mode. Motors can be powered from 24V and consume up to 0.5A of current.

ATtiny2313 microcontroller sends control pulses via ULN2803A chip, which can drive up to 500mA. Firmware is developed by using BASCOM AVR software. Or you can just download hex file which is ready to flash to microcontroller. This might be useful device for testing stepper motors.

Measuring device is combined of mini application module with Atmega128 microcontroller and two SFR04 sonic modules. Measuring principle is very simple. Measure time between sonic transmission and echo reception and then divide it by sound speed in this environment. Timing is explained in this diagram.

Calculated distance is displayed on LCD screen. Sonic distance meter can measure distances from 3cm up to 3 meters and can reflect form 3 cm obstacles at 2 meter distance. I would say quite good addition to some robotic platform. Source codes are written for AVR-GCC compiler and can be downloaded form site.

There are many versions of DTMF decoders outside the Internet, but all are doing pretty the same - decoding dual tone codes in to digits, that can be later interpreted by microcontroller. This device uses an integrated decoder chip MT8870DE which decodes all 16 DTMF tone pairs in to 4 bit code.

AVR Microcontroller reads these codes and outputs them to LCD as characters. DTMF receiver stores last 234 received digits in EEPROM that can be viewed by scrolling an LCD character line. DTMF Decoder also can be connected to PC via RS232 interface. So each time TDMF signal is received it sends digit to Terminal. Program is written by using free WinAVR GCC compiler tools.

The latest keyboard version is an evolution of older one which was based on ATtiny2313 and could be connected to PC via PS/2 and was based on Attiny2313 microcontroller. Latest wearable keyboard is ported to at90usbkey demo board and can be connected to PC via USB.

Keyboard is able to produce all usual characters with few keys that are pressed in groups. It may be convenient to use it on special conditions like for portable computers, palmtops and so on. If you want to study it more John W. McKown provides project files and compiled firmware for free.

Telephone lines that maybe found in your house may be used not only for making calls but also for other purpose like home automation, remote device control. To make it possible there is an interface between phone line and microcontroller system needed.

This DTMF extension is universal module that can be connected to any microcontroller platform. It detects DTMF tones and decodes them to binary digits that can be easily read by microcontroller, which can decide what tasks to perform. DTMF decoder is based on CM8888 chip which is ideal for interfacing with MCU. Here is an example source code for interfacing with AVR ATmega8535 microcontroller which is written for WinAVR compiler toolset.