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

Every circut board requires a power supply to operate properly. Usually, the power supply provides+5Vdc or +3.3Vdc to the whole circut board. There are also instances in which the power supply is not integrated to the circuit board and power must be provided by an external or separate power supply.

Overview

This project is a DIY DC power supply. It can provide a regulated +5Vdc or +3.3Vdc to any circuit board that requires external power supply. It uses two voltage regulators: one for +5Vdc and the other for +3.3Vdc. It also features power-indicating LED (light-emitting diode) and reverse-polarity protection diode.

Hardware

The circuit of this project is very basic. It includes a voltage source connector (JP1) which a regulated or unregulated power source can be connected. Mine is a 9-volt battery connector so that 9-volt batteries can be connected to my board.

When the voltage source or battery is connected properly or in correct polarity, current passes through 1N4001 diode (D1). The purpose of the diode is to block any negative voltage that may damage the whole circuit board.

The voltage that passed through the diode enters 7805 (IC1) which is a 5-volt regulator. This IC provides a constant and regulated +5Vdc output as long as its input voltage is within +7Vdc and +35Vdc.

Another voltage regulator is LM1117-3.3 (IC2) which is a +3.3-volt regulator. Its input is +5Vdc from IC1 and its output is a regulated +3.3Vdc.

Decoupling capacitors (C1, C2, C3) are also found in the circuit. These capacitors filter the inputs and outputs of each voltage regulator and they enhance the regulating capabilities of each voltage regulator.

The dual-row male header connectors (JP2 and JP3)  included in the circuit can be used to provide power to different circuit boards that require +3.3Vdc or +5Vdc. The light-emitting diode (LED1) serves as a power indicator.

Build it…

If you want to build it, you may download the Eagle schematic and PCB files here.

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

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;
  }
 }
}

USB has established itself as the new standard for connectivity. That is why USB connectivity has become the “holy grail” of most embedded applications.

Well, let me get straight to the point. If you want to start developing projects with USB interface, you want to have  the  proper development tools. To have the tools that you need, you either have to buy or to do-it-yourself.

If you want to build a USB development board yourself, here is one for you.

 This development board features Microchip’s PIC18F4550. This development board is a simplified version of Microchip’s PICDEM Full Speed USB. It has one trimmer for ADC, LEDs, push buttons, and USB connector. Most of the pins of PIC18F4550 are brought out to header connectors. It is powered by USB port. Lastly, it is compatible with Microchip’s MCHPFSUSB USB Framework.

Since this development board is a simplified PICDEM FS USB board, hex files can be loaded to PIC18F4550 using the USB bootloader provided by Microchip. Microchip also provided a software tool to download hex files to PIC18F4550.

Here is a video of my development board in action.

Aside from the software tool, Microchip also provides a lot of application notes, sample codes, and libraries to help developers in developing USB embedded applications.

I tried writing a simple code using CDC and here is the video.

Download

The schematic of the board can be downloaded here. You will need Eagle CAD to open the schematic file.

The 8051 is a popular 8-bit single chip microcontroller which was first introduced by Intel. The first 8051 is a 40-pin microcontroller which has 4kB of program memory, 128 bytes of RAM, 2 timer/counter, 1 UART, and six interrupt sources.

Later on, the 8052 microcontroller was introduced. The 8052 microcontroller is a better version of 8051 microcontroller. It has 8kB of code memory and 256 bytes of RAM. It also has an additional timer.

8051 became very propular and it became an industry standard. Due to its popularity, many semiconductor manufacturers like Atmel, Infineon Technologies, Maxim Integrated Products, NXP, ST Microelectronics, Silicon Laboratories, Texas Instruments, Cypress Semiconductor, etc have included 8051 in their line of products.

What is AT89C2051?

AT89C2051 is manufactured by Atmel and it is a member of 8051 family of microcontrollers. Unlike the original 8051 microcontroller which has 40 pins, AT89C2051 has only 20 pins which makes it ideal for 8051 beginners. It takes the standard features of the original features of 8051 except that it has only 20 pins compared to 40 pins of the original 8051. However, AT89C2051 is made of flash program memory and it has additional on-chip analog comparator.

AT89C2051 Pin Diagram and Description

VCC

This pin is the supply voltage pin. The voltage range that can be supplied to this pin is from 2.7 volts to 6 volts but the most commonly used is 5 volts. Just remember to put a decoupling capacitor across this pin to filter out sudden voltage changes in the supply line and put the capacitor as close to VCC pin as possible. Typical values for the capacitor is 100nF.

GND

This is the pin for ground.

XTAL1 & XTAL2

These are the input and output, respectively, of the inverting oscillator amplier located inside AT89C2051. The inverting oscillator amplier can be used as an on-chip oscillator as shown below. Either a quartz crystal or a ceramic resonator may be used. The values of C1 and C2 can be from 20pF to 40pF if a quartz crystal is used and 30pF to 50pF if a ceramic oscillator is used. Frequencies can be up to 24MHz.

The device can also be driven by an external clock source. Just connect the external clock source to XTAL1 and leave XTAL2 unconnected.

RST

This is the input for device reset. The device is being reset as soon as the RST pin goes HIGH.

There is one thing that must be considered for this pin. The  AT89C2051 must operate as intended as soon as it is powered up. To be able to make that happen, AT89C2051 must perform the first instruction located in its program memory. Therefore, the MCU must undergo a reset upon powering up and this is called the power-on reset. The power-on reset for AT89C2051 will only occur when there is a capacitor across VCC and RST pin and a pulldown resitor from RST to ground. The typical configuration for the RST is shown below.

P1.0 – P1.7

Pins P1.0 to P1.7 are the pins of Port1. These pins are bidirectional which means any pin of Port1 can be used as an input pin or an output pin. Pins P1.2 to P1.7 have internal pullups but pins P1.0 and P1.1 require external pullups. However, pins P1.0 and P1.1 are also used as inputs of the on-chip analog comparator.

P3.0 - P3.7

Pins P3.0 to P3.7 are the pins of Port3. Like the Port1, Port3 is also bidirectional and all pins have internal pullups. P3.6 can not be accessed externally because it is hard-wired internally to the output of the on-chip analog comparator. Other functions of the pins of Port3 are shown below: 

AT89C2051 Basic Hardware Configuration

The image above shows the summary of what was just discussed and it shows the basic hardware configuration to make AT89C2051 work.