To solve those problems, I came up with a second version of digital thermometer.

This version of digital thermomter is basically the same as the previous one. However, this version of digital thermometer solves the problems encountered previously. There is also some improvements in the aesthetics aspect and also in the firmware.

I used a voltage regulator with a higher current rating. This is to avoid the regulator to heat up easily and to dissipate any heat as fast as possible. I also put the voltage regulator as far from the sensor as possible.

I also used a smaller and better seven-segment display. This has resulted to a smaller but more beautiful board. It also resulted to easier PCB routing.

However, I kept LM35 as the sensor. I had no reason to change the sensor at all. Besides, this temperature sensor is probably the easiest to use.

To keep the functionality simple and the same, I did not replace the microcontroller that I used in the first version. I kept ATtiny26 as the brain of the digital thermometer. It is easy to use and just enough to my application.

Build it…

If you are interested to build this project, here are the source files for you: digitalthermometer

Features

The microcontroller used in this project is ATtiny2313. This microcontroller is from the AVR family of microcontrollers of Atmel. It has 2KB of flash memory for program storage, 128 bytes of RAM, and 128 bytes of EEPROM. It also has enough I/O ports for this project, USART for serial communication, and it has up to 8MHz of internal oscillator.

The TX and RX pins of the microcontroller are brought out to male headers for future use. The pins can be used to communicate with PC or other devices using UART. Therefore, this project can be customized so that its animations would be programmable using a customized PC software.

The project is powered by four AA batteries. The battery holder can be mounted on the copper side of the PCB which makes the project more compact.

The 8×8 matrix can be made detachable. Female header connectors can be used as the LED matrix socket. This makes the LED matrix easily replaceable and reusable.

Buid it…

If you are interested in building the project, you can download the Eagle schematic and PCB files here.

While building it, make sure that you solder a jumper wire beneath the microcontroller as shown below:

Sample…

Here is a demo of the project.

The source code of the demo is compiled using WinAVR and AVR Studio and it can be downloaded here.

SOURCE FILES

PCB and SCH

Sample code

Please continue to read as I go a bit deeper to the details of what builds this easy project.

The Microcontroller

This project features ATtiny26L microcontroller. This microcontroller is from the AVR family of microcontrollers  manufactured by Atmel. It has 2Kbytes of flash memory and 128 bytes of SRAM which is enough for this project. It also has several 10-bit ADC channels, more than enough for the analog temperature sensor, and it has enough digital I/O pins for the seven-segment displays.

The Temperature Display

To display the temperature, I used four common anode seven-segment displays. The seven-segment displays are driven by PNP transistors and a special technique called “multiplexing” is used to effectively control the displays using only a few digital I/O pins.

Notice how I mounted the fourth seven-segment display by reversing it  to display the °C sign.

The Sensor

The sensor used in this project is LM35. LM35 is an analog temperature sensor and it has a sensitivity of + 10.0 mV/°C. It is accurate enough and it is suitable for different applications. It is rated for full -55° to +150°C range.

]]> http://voltsandbytes.com/diy-digital-thermometer/feed/ 3 http://voltsandbytes.com/8-pin-avr-based-mood-lamp/ http://voltsandbytes.com/8-pin-avr-based-mood-lamp/#comments Tue, 22 Dec 2009 15:04:59 +0000 jer http://voltsandbytes.com/?p=212

I got a sample of a RGB LED (Red Green Blue Light Emitting Diode). So, I decided to make something fun out of it. Using an 8-pin AVR microcontroller, ATtiny45, I made a simple prototype to control the RGB LED using PWM or Pulse Width Modulation.

Then, I put the prototype inside a translucent candle vase. The vase diffused the light from the RGB very nicely and below is the video of the result.

I soldered a potentiometer to ATtiny45 to provide an input to its on-chip ADC or analog-to-digital converter. The rate of color transitions of the RGB LED can, then, be controlled by adjusting the potentiometer.

The following are the pictures of the prototype. No printed circuit boards were used to simplify the project. The project is powered by two AA batteries.

Below is the schematic of the prototype.

The following is the source code for the project. The compiler that I used is WinAVR.

#include <avr/io.h>
#define F_CPU 1000000UL
#include <util/delay.h>

int main(void)
{ unsigned char a=0,b=0,c=0,aa=0,bb=0,cc=0,temp;
 DDRB=0xFF;
 PORTB=0xFF;

//initialize ADC
 ADMUX=0b00100011;
 ADCSRA=0b10000100;

//Set OC0A on Compare Match, clear OC0A at BOTTOM
 TCCR0A|=(1<<COM0A1); 
 TCCR0A|=(1<<COM0A0); 
 //Set OC0B on Compare Match, clear OC0B at BOTTOM
 TCCR0A|=(1<<COM0B1); 
 TCCR0A|=(1<<COM0B0);
 //Fast PWM, TOP=0xFF, Update of OCRx at BOTTOM
 TCCR0A|=(1<<WGM01);     
 TCCR0A|=(1<<WGM00);
 //clkI/O/(No prescaling)
 TCCR0B&=~(1<<WGM02); 
 TCCR0B&=~(1<<CS02);  
 TCCR0B&=~(1<<CS01);
 TCCR0B|=(1<<CS00);

OCR0A=0×00;
 OCR0B=0×00;

//PWM1B: Pulse Width Modulator B Enable
 GTCCR|=(1<<PWM1B);
 //OC1x Set on compare match. Cleared when TCNT1= $00.
 GTCCR&=~(1<<COM1B1);
 GTCCR|=(1<<COM1B0);
 //clock select bits
 TCCR1&=~(1<<CS13);
 TCCR1|=(1<<CS12);
 TCCR1&=~(1<<CS11);
 TCCR1|=(1<<CS10);

//OCR1B=0xFF;
 //OCR1C=0xFF;

while(1)
 { ADCSRA |= (1<<ADSC);
  while((ADCSRA&0×10)==0×00);
  temp=ADCH;

OCR0A=c;
  OCR0B=b;
  OCR1B=~a;

while(temp>0)
  { temp–;
   _delay_ms(1);
  }

if(aa==0)
  { a=a+1;
   if(a==0xFF)
   aa=1;
  }

  if(aa==1)
  { a=a-1;
   if(a==0)
   aa=0;
  }

if(bb==0)
  { b=b+3;
   if(b==0xFF)
    bb=1;
  }

  if(bb==1)
  { b=b-3;
   if(b==0)
    bb=0;
  }

if(cc==0)
  { c=c+5;
   if(c==0xFF)
    cc=1;
  }

  if(cc==1)
  { c=c-5;
   if(c==0)
    cc=0;
  }
 }
}

The development tool that I am talking about is the AVR Dragon.

AVR Dragon is highlighting In-System-Programming, High Voltage Serial and Parallel Programming, JTAG, and debugWire. You can almost do all kinds of programming and debugging methods with those features. Aside from that, the PC communication and power is provided by USB. It is fully supported by the free AVR Studio IDE which makes developing AVR projects very fast.

Using the AVR Dragon requires some hardware setup first. Each target AVR MCU must be connected to the proper header pins provided with the board. However, the user must provide and solder the other remaining header pins to fully use it. Also, one major drawback of the AVR dragon is that it does not come with wire connectors and USB cable.

All in all, I am a very satisfied user of AVR Dragon and it saved me from a lot of hassles. For a retail price of USD49, it gives me the comfort that i deserve when it comes to developing projects using my favorite AVR microcontrollers.