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Did you finish your digital thermometer?

I have noticed that there are lots of temperature sensor projects out there in the internet, but the question is how many of them end up to be left on breadboard. I also found myself not hawing one that I could do simple temperature readings when ever and where ever I need. Lets see another simple temperature probe which is also a breadboard prototype. But with some work can be made in to portable probe. rahulkar built this thermometer using Attiny85 microcontroller and LM35 temperature sensor. His probe is able to measure temperature from 0 to 150ºC or in Fahrenheit (selectable with button). Since Attiny is small IC he used MAX7219 7-segment LED display driver which accepts serial data. So he placed five digits to display full range of temperatures. He programmed Attiny85 with Arduino code which takes only few lines. To make probe more useful I would change circuit a bit to extend temperature range to negative as sensor can measure from -55 to +150ºC. Continue reading

LM35 thermometer based on Attiny26

There will be never enough of thermometers as we know. There are tons of projects with different sensors and displays. You can choose the one which suits your needs best. SO here is another simple to built thermometer by using LM35 temperature sensor. Temperature sensor gives 10mV per ºC. This means that at 25ºC the output will be 250mV. If you connect this sensor directly to 5V referenced MCU with 10-bit ADC accuracy, you get 4.9mV step or 0.49ºC resolution. In order to increase resolution there is an operation amplifier used which adds gain of 11 to sensor signal. Gain increases resolution by order of magnitude – to 0.0445ºC. Attiny26 reads temperature value and displays it on 4-digit 7-segment LED display. LED display is common anode where each anode is driven with transistor key. Microcontroller simply scans through digits at 60fps rate to make impression that all digits are light at once. Power supply is provided by using 7805 voltage regulator which drops voltage from 9V to 5v. For longer battery life there could be switched DC/DC converter used. Continue reading

AVR based thermostat for home heater

Candrian wanted to optimize home fireplace which heats water for radiators. The idea is first to heat up water inside fireplace and then open valve to let hot water to radiators. Original thermostat suppose to work that way, but in reality thermostat shuts the valve once cool return water cycles around. In order to prevent opening and closing valve frequently he designed his own thermostat which would allow to set time span when valve stays open even if water temperature drops. Some may not agree that this idea is good, because first priority would be to keep fireplace water temperature at working level to get optimal burn and prolong life-cycle due to condensation and corrosion. Anyway, everyone have their own needs and lets focus more on electronic part of thermostat, Schematic of thermostat is pretty simple. It is built around Atmega198 microcontroller which controls couple mechanical relays. They drive electrical valves. Temperature is captured by using LM35 sensor which is attached to microcontrollers analog input. Standard LCD and rotary encoder gives simple and intuitive user interface where time delays and… Continue reading

Really simple Attiny26 based digital thermometer

Since most of microcontrollers already have ADC built in you don’t need digital temperature sensors in order to measure temperature. Such sensor can be well known LM35 precision device which outputs linear 10mV per Celsius. If using analog sensor for controlling, you practically don’t need a microcontroller to get desired results. Anyway if you need to display temperature value properly you might need an MCU for this. Jerson have published his small design where he interfaces LM35 temperature sensor to Attiny26 microcontroller and displays it on four 7 segment LED display. It would work if sensor were connected to ADC directly, but with 10mV step per Celsius you would lose a resolution as ADC accepts much wider range of analog signals than sensor produces. To solve this problem he used OPA344 based amplifier that rises sensor voltage to appropriate level and thus have decent resolution of 0.0445 Celsius. Continue reading

Dual Thermometer with Graphical LCD

Dont know if using grafical LCD is very effective way of building thermometer, but if you have few spare laying on your desk – why not. As a result you can bild very cool thermometer as Andrei did. He used few standard parts like PIC16F88 microcontroller, KS0108 graphical LCD and couple LM35 temperature sensors. He also made Proteus VSM simulation – this is much easier to test firmware or even modify existing one without building real board. All necesasry files including source code written for CCS C compiler, Proteus VSM simulation file and hex you can find here. Continue reading