If you go to AVR site and open an AVR application note AVR053 you will notice that there are different RC oscillators installed in to AVR chips during history. Simply speaking each new version of oscillator introduces better features and improvements. But is it really truth? ChaN has made interesting research on these oscillator version. He simply tested output signal with fixed width and measured timing fluctuations of it. And he found out, that RC generator frequency slowly fluctuates during time.
AVR internal oscillator jitter research - [Link]
This is small versatile USB board developed by Brian Schmalz. He used PIC-USB capable microcontroller for easy USB interfacing and this way got simple parallel port replacement.
There is not much about circuit itself as there is only PIC microcontroller, USB connection and I/O pins. Such simple design allows making smal PCB that may fit anywhere starting from integrating in to test-boards and ending as stand alone applications. Author have compiled a nice list of various board versions that include different PIC microcontrollers, different PCB types that can fit in various applications like for plugging to breadboard, or very small SOIC board for tiny projects. Author also provides a list of various firmware versions along with bootloaders. To make things more easier there are few demo applications available for testing or modifying to your own needs. [via]
Simple PIC USB I/O board - [Link]
Dubravko Gacina have sent a link to his project that was participating i a circuit cellar MSP430 design contests some time ago. This is a digital temperature and humidity metter based on MSP430F413 microcontroller. MSP430 microcontrollers are known as ultra low power MCU devices that are ideal for battery operated devices. Sadly that there is no more information including circuit and firmware.
MSP430 TeHuMet project - [Link]
Tomward made these great business cards that can dial you! he writes -
I bet nobody has given you a business card before that actually dials you up by itself! Read on to find out how I did it ….
Do you like making things? Do you do it for money, or would like to? If so, you need a business card. These can be your best advertising, but we all know business cards are boring and get thrown away. I have toyed with plastic or etched stainless cards before – these are really cool, but cost a lot, and are not really distinctively “you”.
“The Open Source project Liberlab aims to help democratize educational scientific experimentation through the creation and use of a DIY digital lab at a very low price ( ~ 15 €/$). Liberlab can also be used to learn about robotics, automation, human-machine interface or interactive arts.”
Liberlab – Open source data acquisition and control - [Link]
Learn how to interface PCF8583 Real Time Clock with an AVR microcontroller. Source code is included.
The PCF8583 is a clock/calendar circuit based on a 2048-bit static CMOS RAM organized as 256 words by 8 bits. Addresses and data are transferred serially via the two-line bidirectional I2C-bus. The built-in word address register is incremented automatically after each written or read data byte. Address pin A0 is used for programming the hardware address, allowing the connection of two devices to the bus without additional hardware.The built-in 32.768 kHz oscillator circuit and the first 8 bytes of the RAM are used for the clock/calendar and counter functions. The next 8 bytes may be programmed as alarm registers or used as free RAM space. The remaining 240 bytes are free RAM locations.
Real Time Clock PCF8583 - [Link]
The idea of this project was to build DIY autopilot kit that anyone could build and use in their flying models like helicopters. Autopilot uses two dual axis ADXL202 accelerometers to read 3D acceleration, also it reads attitude, engine stats, position, payload stats. All these readings and control is operated by realtime system OS, which reads each sensor at some predefined rate. This is really quite complex system which seems to be stil under development – but it already gives positive results. [via]
Autopilot for autonomous aerial hobbyist vehicles - [Link]
There may be some situations when it is hard to use a tachometer only because it is impossible to read revolutions per minute mechanically. The only way is to read RPM without touching rotating shaft. This great design was constructed by Ibrahim Kamal who used an IR signal to transmit and receive it reflected from reflective stripe fixed to rotating shaft. Device is controlled by AT89S52 microcontroller which counts reflected pulses and displays value on LCD. RPM counting algorithm uses last three times between pulses and this way constantly gives instant RPM value. RPM meter consists of two parts: microcontroller board and IR proximity sensor connected to microcontroller board via simple 4 wire cable. Project files are available for download in a single zip.
Contact-less tachometer counts up to 99kRPM - [Link]
This simple device, designed by Wichit Sirichote, measures the quality of AC voltage. The device measures 3rd harmonic which is used to find the distortion value comparing to fundamental frequency. Device calculates DFT of signal which is captured via step down isolation transformer and 10-bit ADC. Testing showed that clean sine wave gives less than 0.5% of distortion, while square wave gives about 33%. Project description includes detailed measurement theory outline and practical examples as well. Project is built on test board which was developed for general purposes. Source code is available for download. [via]
PIC18F2550 based harmonic distortion meter - [Link]
RFM12 is a transmitter and receiver module in single board. It can be powered by using 2.2V to 5.4. It makes ideal module for embedded systems. Module communicates via SPI interface. Wigbert Picht and Dirk Milewski have made simple Atmega8 tesboard, where RFM12 module is soldered as SMD element and can be configured with jumpers. There can be any sensors connected to this board like temperature. [via]
Interfacing RFM12 transceiver module - [Link]