Friday, October 18, 2013

[TC] Building an analog meter clock with Atmel and Adafruit


“We wanted to design a microcontroller board that was small enough to fit into any project – and low cost enough to use without hesitation,” Adafruit’s Limor Fried (aka LadyAda) explained. “[It is] perfect for when you don’t want to give up your expensive dev-board and you aren’t willing to take apart the project you worked so hard to design.”
Although the Trinket launched in September, the ATtiny85-powered Trinket has already tipped up in a number of projects including a sound-reactive color LED organ, IR control device, Tap Tempo and a temperature/humidity sensor. Today, we’ll be talking about building a Trinket-powered analog meter clock. As Adafruit’s Mike Barela notes, the Trinket is a perfect fit for clock projects, as the platform is small and easy to hide behind a larger display.
“Clocks don’t need a lot of logic, this example only has maybe 20 lines of code, [while] adding a digital display via I2C is possible using seven segment or character-based displays (with the library code posted for other projects),” Barela wrote in a detailed tutorial on the subject. ”This [specific] project interfaces Trinket to the the Adafruit DS1307 real-time clock (RTC) breakout board to form a clock. But in a twist, the display is done using two analog meters. One for hours, one for minutes.”
According to Barela, the Trinket is capable of outputting to a meter without digital to analog converters.
“Trinket has pulse width modulation (PWM) on three of its pins. The meter uses a moving coil inductance movement, acting to average the indication of current flowing through it,” he continued.
“If you have narrow pulses, the average voltage it sees is lower, thus the current is lower for the fixed resistance attached to it. For wide pulses, the meter sees nearly the supply voltage and will stay around the full scale. This circuit varies the pulse width sent to the meters proportional to the hour of the day and the minutes after the hour.”
For two meters, says Barela, two of the three PWM pins on Trinket will be used (the third is also an I2C pin connected to the clock module). Although there are many ways to display the finished product, Adafruit decided to go with the meters “free-floating” in a colorful box, rather than a cabinet or plexiglass display.
To kick off the project, Barela recommends Makers first unpack their Trinket. Those using a breadboard or Perma-Proto board will want to solder on the (provided) header pins. After unpacking the DS1307 kit and building the circuit, Makers are instructed to modify the Arduino IDE to work with Trinket by adding the hardware definition file, the avrdude.conf file – while changing the ld.exe program from the 2008 dated version to the 2009 dated version and installing the driver for USBtinyISP appropriate to your operating system.
“To prepare the Trinket for other programs, you will want to first load the Trinket Blink sketch into the Arduino software then load it onto the Trinket to verify everything works well. You must press the hardware reset button on the Trinket then quickly press upload in the Arduino software to upload a sketch,” Barela added. “If you get an error, try the reset-upload process again. If you continually cannot load the blink sketch, check to make sure the Trinket is connected (without any wires connected to pins #3 and #4) and the Arduino IDE software has all the required changes.”'


Source: http://atmelcorporation.wordpress.com/2013/10/18/building-an-analog-meter-clock-with-atmel-and-adafruit/

[TC] "Biocrats BharatOvation 2013" Organised By University Of Pune on 10th and 11th Dec, 2013.



Objectives of Event:

  • Creation of a platform in India for visionary Innovators, Industrial Houses, Venture Capitalists, Angle investors, Govt. policy makers, Scientists and Technocrats to discuss innovations, especially aimed at the bottom of the pyramid, with regards to funding and further technology development possibilities.
  • Provide a unique platform to grass-root innovators to showcase their innovations to masses and directly tap into market and potential customers.
  • Ensure that the deserving innovations are taken up by leading industrial houses for further development and commercialization.
  • Showcase capability of Indians to 'innovate under constrains'.
  • Promote, gather and felicitate 'out-of-box' ideas from masses
  • Generate new scientific ideas and concepts relevant for the common people
  • Sensitize, encourage & initiate the process of innovative thinking amongst common people



Submit Your Idea athttp://ii.unipune.ac.in/site/join?0%5BshowRegForm%5D=0


Thursday, October 3, 2013

[TC] Circuit for Over-Voltage Protection

Over-voltage protection circuits are used to protect voltage-sensitive loads. Voltage transients may occur due to a number of reasons such as transformer switching, load switching, and short/open circuit in rectifier and regulator circuit. Such transients can affect proper functioning of an electronic circuit or even damage it. Hence it is necessary to use an over-voltage protection circuit to protect expensive loads against all the sources of voltage transients.



In electronics engineering, where over-voltage protection experiment is included in the syllabus, the present circuit can be used to very effectively demonstrate the effect to students.

Circuit and working


Fig. 1 shows the demo circuit for over-voltage protection. It is built around a rectifier comprising four 1N4007 diodes (D1 through D4), 10V voltage regulator IC 7810 (IC1), SCR 2P4M (SCR1), transistor BC548 (T1) and a few other components. SCR1 is used as a protective component. 

Fig. 1: Demo circuit for over-voltage protection

If voltage exceeds beyond the withstanding voltage capacity of the device that needs to be protected (6V bulb here), the circuit disconnects the device from supply. To demonstrate this, potmeter VR1 connected across regulator IC1 is used to increase the voltage at the output of regulator IC1. When the output voltage of IC1 increases, voltage at the base of transistor T1 also increases, which triggers SCR1 through resistor R6. Once SCR1 triggers, fuse blows and disconnects the power supply from the device.



For demo, set VR1 at the maximum limit (say, 1k) and switch on the circuit. Using a digital multimeter, measure the output at CON3. It should be around 10.3 V. Now reduce VR1 resistance in steps. At around 800 Ω, the multimeter reads 10.9 V. Reduce the resistance further until SCR1 fires. Experimentally, it was found that at around 680 Ω, the SCR turns on after receiving a triggering pulse and a heavy current passes through the fuse wire. Due to this, the fuse wire blows and the load disconnects from the supply.


Construction and testing


An actual-size, single-side PCB of the demo circuit for over-voltage protection is shown in Fig. 2 and its component layout in Fig. 3. After assembling the circuit on PCB, enclose it in a suitable box.




Fig. 2: An actual-size, single-side PCB of the demo circuit for over-voltage
protection



Fig. 3: Component layout for the PCB
Download: http://www.electronicsforu.com/electronicsforu/circuitarchives/my_documents/my_files/C24_overvoltage.zip


To test the circuit for proper functioning, switch on S1 and measure the input voltage (230V AC) between TP2 and TP3. Also verify the output of IC1 as 10 V at TP1 with respect to TP0. Check voltage variation at the base of transistor T1 corresponding to change in the resistance value of VR1.  


Source : http://electronicsforu.com/
Authors : Milind M. Sutar, Dr J.L. Bhosale and Prof. P.B. Joshi