The circuit uses a constant current drive and a four wire connection to the probes. This allows almost any length of probe connecting cable without re-calibration. Surface mount chips are wonderful, but for prototype work these can be difficult to use. If you only have SMD parts available to make it easier you can construct a SO to DIP adapter.
Two Channel Thermometer: [Link]
This simple circuit is designed to report the temperature via any standard FM broadcast band radio at regular intervals. It uses a simple low bit rate tone signalling scheme which can be interpreted easily by both humans and machines. Such a device can be used stand-alone or as part of a PC-based weather station or HVAC system.
There are endless practical applications for such a device, just think about how many time you wanted to measure a temperature and for that you needed to run wires to the sensor. Now with this circuit you can place the device where you need the temperature reading and no more wires need to be connected.
Wireless Digital Thermometer: [Link]
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 output voltage is 10mV/ºC . The output voltage is converted by the AD convertor of the ATMega8. The temperature is displayed on an LCD module. In this example the thermometer has a range of 0ºC to 40ºC and a resolution of 0.5ºC. If you want to have a readout in Fahrenheit you can use the LM34.
LM35 Based Thermometer Display Temperature on LCD: [Link]
This 3-digit digital thermometer is easy to build for beginners or hobbyits. PIC16F628 is used to read digital values of temperature from a DS1820 sensor. All 7-segments are driven by a power logic 8-bit shift register TPIC6B595 with open collector output. For the 7-segment we need 12V volt to drive it because it has 3 LED per one segment. Source code in C Compiler is available.
3-Digit Digital Thermometer: [Link]
At this thermometer, the IC thermo sensor (S8100) or the diode (1S1588) is used as the thermo sensor. When using the IC thermo sensor, the thermometry to +100°C from -40°C is possible. Also, when using the diode, the measurement to +150°C from -20°C is possible. Both sensors are contained in the kit.
LCD Thermometer With Range From -20 to +150°C: [Link]
