Air pressure, temperature and altitude with BMP280 sensor

BMP280 is a digital air pressure sensor especially designed for mobile applications. It is a very small device, having a footprint of 2 by 2.5 millimeters. Interfacing with a development board would be difficult if breakout boards wouldn't exist. Even so, there's another issue: sensor's nominal voltage is 1.8 V. Fortunately, it can handle 3.3 volts. BMP280 can measure atmospheric pressure and temperature. Since there is a correlation between pressure and altitude, the latter can be estimated.

I ended up wiring this sensor to a 5 V development board because of the display. Pressure, temperature and altitude required 3 rows, so I used my ST7920 graphic LCD. Although this controller works at 3.3V, the way my display is hardwired by manufacturer does not because you cannot increase contrast enough. I connected the display in SPI mode, so only 4 wires are used (3 for SPI and 1 is reset). The BMP280 supports either SPI or I²C interface. Because the only level shifter I have is one I built a while ago for I²C, this is the protocol I wrote the code for.

The BMP280 sensor on the breadboard

Arduino Thermometer with... TV Output

Analog video is getting replaced by digital signals which provide better resolution and picture without noise or interference. Although receivers for digital signals are cheap and popular, devices for generating such signals are expensive and intended for professional use only. On the other hand, analog video is easy to generate with simple hardware. You can even broadcast it over RF (on wire, not on air) with common modulators (standalone devices or modules from video game consoles, set top boxes, VCRs etc.).

An easy way to generate video signal is by using a microcontroller and some resistors. I'll use for this purpose an Arduino board (ATmega 328p) with the TVout library. The video signal is of low resolution and black&white. But it can be used to display data on a TV screen. If you no longer own a TV with analog video input, an USB capture card can be used. TVout library is interrupt based, therefore will interfere with some of other interrupt dependent microcontroller features.

Compute Heat Index with Arduino and DHT Sensor

The heat index is a parameter that takes into account temperature and relative humidity, to determine the apparent temperature or the human perceived equivalent temperature. Heat index was developed in 1978 by George Winterling and was adopted next year. It is also known as humiture, according to Wikipedia contributors.

To compute this index, you need to know current temperature and relative humidity. An easy way to find both is by using an Arduino development board with a DHT sensor (DHT11, DHT22). These sensors measure temperature and humidity and send it to the microcontroller using a digital protocol. Thus, there is no need for calibration. You can read the values directly from the sensor module. However, you should take into account that the accuracy of these sensors is not the best. DHT11 has an accuracy of +/-5% for humidity and +/-2 degrees Celsius for temperature. DHT22 (AM2302) is slightly better with an accuracy of +/-2% for humidity and +/-0.5 degrees Celsius for temperature. More than that, DHT22 has extended ranges for both temperature and humidity.