PIR sensors are also referred to as Passive Infra Red sensors. They can detect motion of a human or animal from 2 meters distance.  PIR's are basically made of a pyroelectric sensor, which can detect levels of infrared radiation.

The DHT11 sensor is made of two parts, the capacitive humidity sensor and the thermistor. There is also a basic chip inside that converts the analog signal to a digital signal with the temperature and the humidity.The digital signal is easy to read using a microcontroller. The result is shown on a LCD display.

With this project you can show the temperature on you PC. This thermometer plugs in on any free serial port. It gives temperature readings accurate to 0.5°C with no calibration.The project consists of the ATTiny2313 RS232 board and the DS1621 Thermometer board and software for the PC. It can display both indoor and outside temperature on the PC screen (see picture below).

This small thermometer board uses the Microchip TCN75 device. It is a cheaper clone of the LM75, it costs about 2,50 Euro. The TCN75 comes in a SO8 packaging. The TCN75 is a serially programmable temperature sensor.

This small thermometer board can be connected directly to PORTD of the AVR 2313 Project board. It uses the Dallas DS1621 Digital Thermometer and Thermostat chip. The DS1621 measures temperatures from -55° to +125° in 0.5° steps and doesn't need calibration or external components. It has also a build-in thermostat with high and low set-points which can be programmed by the user.

The LM35 of National Semiconductors that is used in this project is a precision centigrade temperature sensor, which has an analog output voltage. It has a range of -55ºC to +150ºC and a accuracy of ±0.5ºC .

The LM335AZ is a cheap (0,75 €) temperature sensor that reads the surrounding temperature and is calibrated in degrees Kelvin. The LM335 has an output from −40°C to 100°C.

Measure the temperature with the SPI digital temperature sensor and show it on an LCD display.

The LM335AZ is a small low cost (0,75 €) analog temperature sensor that reads the ambient temperature and is calibrated in degrees Kelvin. The LM335 has an output from −40°C to 100°C.

A photocell or photo resistor is a Light Dependent Resistors (LDR). LDR's are sensors that detect light. They are small, inexpensive, low-power, easy to use and don't wear out.