Thursday, September 30, 2010

Dual Scale Digital Room Thermometer using PIC Microchip

Digital thermometers are popular among hobbyists. Here is one based on PIC microchip that measures temperatures from -55C to +125 C using DS1820 sensor and display on a character LCD in both C and F scales. The firmware is written in mikroC compiler from mikroelektronika,  and the circuit is easy to build. The firmware provided takes care for entire temperature range of sensors.

Monday, September 27, 2010

3-wire Serial LCD for PIC12F Series Microcontrollers

Low pin-count microcontrollers like PIC12F series don't have enough I/O ports to directly drive a seven segment or character LCD display. However, it can be done with the use of a serial-in-parallel-out shift register. The idea is to first transfer the character data or LCD command serially from the microcontroller to the shift register, and when it is ready at the parallel output of the shift register, send an Enable signal to the LCD module to accept it. Of course LCD pins are connected at the parallel output of the shift register. The circuit below shows how to use a 74HC595 shift register for this purpose.

Saturday, September 25, 2010

PIC12F683 Timer1 Module + Frequency Counter + MikroC

The Timer1 module inside PIC12F683 is a 16-bit timer/counter. If used as an asynchronous counter, this module can be used for counting the frequency of an external clock source applied to its GP5/T1CKI port. The following example is a 0-65535 Hz frequency counter using Timer1 module of PIC12F683. The Timer1 module is reset first and then turned ON for 1 sec to count the clock pulses arrived at its T1CKI port during that period. The number of pulses arrived in  second is frequency itself. The measured frequency value is sent to PC through serial port and displayed on a hyperterminal receiver window. If the external clock frequency is over 65535 Hz, Timer1 overflows and an interrupt is generated. In case of the overflow, "Frequency out of range " message is displayed on the window. A 555 Timer IC running as an astable multivibrator is used as the external clock source.

Tuesday, September 21, 2010

Various Audio Amplifier IC Circuits

Here are some of the popular audio amplifier IC circuits.


6 Watt Audio Amplifier based on TA7222AP IC

This circuit provides audio amplification of approximately 6W. It uses TA7222AP audio amplifier IC that can deliver 6W to a 4 Ohm speaker. This IC has other nice features like muting function, low distortion, high ripple rejection, short circuit protection, thermal shut down etc. This amplifier can be operated from 8 to 12V and this makes it ideal for car radio applications.


Variable Dual Power Supply for your Experiments

This power supply provides variable positive and negative DC voltage for your experiments. It is based on LM317 (positive voltage regulator) and LM337 (negative voltage regulator) ICs.
The diodes D5 and D6 are to protect external reverse polarities, and VR1A and VR1B (each 2K) are potentiometers to control the output voltages.

High Current (10A) 13.8V Power Supply

This circuit uses LM723 IC that provides a very good voltage regulation. The 3 pass transistors connected in parallel with LM723 require heat sinking. The output voltage is tuned to 13.8V by resistor R9 and the resistor network formed by resistors R4 through R7 controls the current limiting. The LM723 limits the current when the voltage drop across R5 approaches .7 volts. The thermal runaway is not a problem here because the circuit samples the collector current through pass transistors.

Variable DC Power Supply for Hobbyists and Students


A variable DC power supply is one of the most important tools for an electronics hobbyist. In order to carry out an experiment you need a reliable DC power source that can be varied according to the need of the experiment. Last week I felt I must have one on my workbench, and thought to make one for myself. This design is very simple but is great for powering almost all kinds electronic projects. It uses LM350 (a 3-pin IC) to generate a variable DC power supply. I would recommend to read the datasheet before doing this project.

The LM350 is an adjustable 3-terminal positive voltage regulator that is capable of supplying in excess of 3A over a 1.2V to 33V output range. They are exceptionally easy to use and require only 2 external resistors to set the output voltage.

Main Features
  • Adjustable output down to 1.2V
  • Guaranteed 3A output current
  • Guaranteed thermal regulation
  • Output is short circuit protected 

Cheap Microcontroller Programmers for Students and Hobbyists

Few years ago, microcontroller programmers and development boards were quite expensive to afford for students and hobbyists. Besides they were not easily available everywhere.When I was in school, we had two AT89C51 programmers in our whole department of electrical engineering and we had to get permission to use them. Things have been changed since then, and now you can buy one for less than $20 online that could fulfill a student's or hobbyists' need.

I am writing this article with the intention to show some cheap microcontroller programmers that you can buy online. The most popular microcontrollers among hobbyists and students are PIC (from Microchip) and AVR (from Atmel). For PIC, people usually recommend to buy Microchip's PICkit because the programming software is maintained by Microchip itself, and the software also provides debugging feature. But the disadvantage is it is little bit expensive for beginners. I don't have PICkit, I bought a third party programmer, it works great. And if you are going to use high level compiler for programming, debugging is rarely used for beginner's level project. But I would definitely recommend one thing: buy USB programmer and not serial or parallel type, because the later two are outdated and modern laptops (and may be computers) don't have them.

AVR Programmers
1. Pololu USB AVR Programmer: The Pololu USB AVR Programmer is an extremely compact, low-cost in-system programmer (ISP) for Atmel’s AVR mirocontrollers. The USB AVR programmer connects to your computer’s USB port via an included USB A to mini-B cable and communicates with your programming software, such as AVR Studio or AVRDUDE, through a virtual COM port using the AVRISPV2/STK500 protocol. The programmer connects to your target device via an included 6-pin ISP programming cable.The programmer is powered by the 5V USB power bus, and it is intended for programming AVRs that are running at close to 5 V (note that the programmer does not deliver power to the target device).
Cost: $19.95 Buy it here:

Monday, September 13, 2010

Mains AC Frequency Monitor using PIC Microchip

This project reads the AC line frequency and displays on a LCD. The 120V AC is first converted to 12V AC using a step-down transformer. With the help of a BJT, the output Sine wave is further converted to 5V square pulses which is fed to TOCKI pin of PIC16F628A. The Timer0 module is used as an 8-bit counter. The counter counts the number of pulses arrived at TOCKI port in 1 sec, which, in fact, is frequency of manis AC, and displays it on a LCD.

Monday, September 6, 2010

PIC16F886 Temperature and Humidity Meter

SHT11 is a digital humidity and temperature sensor on one chip. This project describes the interface between PIC16F886 microchip and SHT11 sensor and displays the measurements on a LCD display.
In order to get temperature or humidity data, SHT11 needs
  • Connection reset sequence (consists of at least 9 pulse while data is high).
  • Transmission start sequence (consists of lowering data while clock is high follow by lowering and highering clock then release data to high).
  • Command byte (consists of 000 and 5bit command code)
  • wait untill measurement compleated.
  • get 2 bytes data
  • get CRC byte if need.