Intelligent bi-colour backlit LCD display’s thermometer ICL7106 PIC16F84A LM324 74HC148


Fig.1 - The thermometer with the green backlight

Fig.1 – The thermometer with the green backlight

What I’m getting ready to explain below, is an original solution I adopted to backlight the thermometer’s project SP0003. Thanks to this, I solved quite easily the main difficulty that consists in generating an even illuminated background to the LCD display using some common LEDs.

At that time, I was also learning how to use the microcontrollers and I wished to make my first real project (and not only on a breadboard) with the PIC16F84A. I programmed the µC for changing the backlight’s brightness according to the room’s light intensity because it could be annoying in the dark, or insufficient in the opposite condition. I also thought that it could be nice switching the LCD backlight colour by pressing a push button.

To complete the project, I inserted a power supply to the thermometer capable of accepting a wide range of DC or AC voltage.

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Precise Thermometer with 3½ Digits LCD Display ICL7106 AD590

Go to the project BP003 if you want to add a bi-colour LED backlight and a power supply board on the thermometer. In addition, an useful video clip is available there to watch the thermometer in action.


Fig.1 – The digital thermometer's LCD display in action

Fig.1 – The digital thermometer in action

I wanted to build this project because I needed a thermometer in my house, but also, because I wanted to have the occasion to use a LCD display for the first time.

I have always been fascinated by LCDs. Their capability to make numbers, letters and drawings on a glass plate is something magic. Thanks to this project I learnt a bit more about them and I discovered the tricks of the wizardry. Despite this, and even if the LCD displays have become obsolete, I still think they are the result of an amazing technology.

I chose to use the ICL7106 as the driver for the LCD display. This specific IC by Intersil, has also inside an A/D converter necessary to “transform” the analogue signal generated by the temperature transducer into a digital one. For practical reasons, I decided to split the project in two different sections, and then, in two different boards: one for the LCD display and another one for the ICL7106 IC.

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