NDIR Based Co2 Meter

The next review is about a home-built Co2 meter, which is built on the concept of NDIR. NDIR stands for non-dispersive infrared sensor which is a simple spectroscopic device often used as gas detector. It is called non-dispersive because wavelength which passes through the sampling chamber is not pre-filtered instead a filter is used before the detector. We already have NDIR based gas-modules which are a common type, small size sensor, using non-dispersive infrared (NDIR) principle to detect the existence of CO2 in the air, with good selectivity, non-oxygen dependent and long life. The sensor used is a MH-Z14 IR module which outputs a PWM wave based on the level of gas detected. It has a sensitivity of 0 to 2000ppm Co2. For those who are interested in the project an inbuilt library has been provided for the AVR Mega controller whose main job is to read PWM and with the help of some mathematical operation, that are not too hard to derive, the level of Co2 is displayed. A rather simple project but it can act as a base… Continue reading

ATmega88 based POV weather station generates its own power

We like POV(Persistence of Vision) projects – specially those with unique ways to transmit energy to the turning row of LEDs (Light Emitting Diodes). This POV however beats the rest that we have seen so far – this one is a freakin weather station. Instead of displaying graphics this POV displays the current temperature and relative humidity. And the best thing we like about this guy? It generates its own energy! It uses a stepper motor as a generator, when a stepper motor is turned current flow through its wires. It is then rectified using a set of diodes and stored into a 6 – capacitor charge bank. The Charged stored in the bank is then fed to a  TPS5420 buck converter that outputs 3.5V – just enough to drive the ATmega88 microcontroller and the 8 – LED array. The ATmega88 is operating at 10MHz while it gathers humidity and temperature data from an SHT21 using I2C protocol. To sync when to start displaying, it uses a hall effect sensor from an old floppy drive  – this is used to determine absolute… Continue reading

A microcontroller based DDS function generator using an AD9833

A DDS Function Generator

First what do we mean by DDS – DDS stands for direct digital synthesis. A DDS chip generates a waveform from an internal ROM with table. The ROM table could contain square, triangular, sawtooth or sine wave forms. A high frequency oscillator is used to drive a DDS chip – the high frequency clock is taken into a large internal divider that in turn would generate clock signals of less than 1Hz. The derived low frequency signal will be used to tell the on-chip digital to analog converter to go to the next value on the ROM table. This particular project makes use of the AD9833 DDS sinewave generator from analog devices. A 50MHz clock was used to drive the AD9833 while an ATmega32 was used as the main controller that takes user input though a numeric keypad, displays the current output through a 16×2 liquid crystal display (LCD) and communicates with the AD9833 through 3 wire SPI. The challenge in building the project comes with the fact that high speed waveforms are difficult to amplify and easily gets infested… Continue reading

A microcontroller based automobile digital RPM meter

Some of the smaller cars available today does not have an RPM meter on them – this would be some trouble since you wont be able to determine the actual speed of the car’s engine, thus will have an impact on the fuel consumption since engines are efficient at a certain range of shaft speed. This project makes use of an AVR microcontroller and a signal conditioning circuit that makes use of an LM324 operational amplifier (Op-Amp). The input signal was taken from the High Voltage (HV line) of the main distributor of the engine. This specific point was chosen since all (gasoline) engines have an HV line. The signal from the HV line is fed into the signal conditioning circuit before being fed to the microcontroller’s PB1 pin. The Timer/Counter1 External Counter Input mode of the PB1 pin is used as an external clocking source for the MCU’s timer1 making it able to do frequency measurements. While another timer (timer0) is used to measure the elapsed time. If you wonder whats in the HV line that makes it a good… Continue reading

LED Dog Collar – keeps your dog safe at night

Ken has two dogs, one of them ‘sunshine’ likes to run around when given the chance to go out. This gives him worries since she could be hit by a car. To lessen his worries he rigged up a bunch of LEDs into a dog collar. The LEDs are connected to an AVR ATTINY2313 microcontroller. Current limiting resistors are used to regulate current that flows through the LEDs. The entire electronic set up including the ATTINY2313 and the LEDs are powered using 3 AAA batteries. The PCB was made using toner transfer method while an arduino was used as an ISP to program the ATTINY2313. The good thing about building DIY stuff in your home is that what ever you do you always find a way to utilize hot glue – the electronic components in the board is covered with hot glue, the LEDs are helt to place by hot glue and the PCB was mounted on the collar with [what else?] HOT GLUE!     Continue reading

RF garage door opener

After Mike moved to his new place, he found that current garage door opener is does not work as expected. So he decided to make his own remote controlled garage door opener. As usual RF link consists of two parts – transmitter and receiver. Building receiving part is easier as there isn’t much restrictions on size and power supply because it always stays inside garage and can be powered with wall wart power supply. So it is based on Olimex AVR-MT-128 development board with LCD. LCD currently displays times the garage door was opened. For RF communications he has chosen cheap 315MHz RF modules. There is more hustle with transmitter as it has to be carried around. It must have decent small size, range and power usage. It is based on Attiny13 microcontroller. As power supply there is a 9V battery used that is scaled down to 5V (wouldn’t call this efficient). Prototype version has proved itself be reliable. Now it time to make it compact… Continue reading