RGB colour-illuminated scaleThis bargraph thermometer from Elektor Labs is based on an Arduino Nano. It offers a beautiful graphical representation of ambient temperature using a Russian IN-9 tube and an illuminated scale with various RGB-controlled colours.
The temperature scale in degrees Celsius as well as Fahrenheit extends from 10 °C to 30 °C / 50 °F to 85 °F.
The circuit consists of a 5-to-150 V "voltage doubler" step-up converter, an IN-9 tube driver based on a low-voltage rail-to-rail opamp, two RGB LEDs and of course the Nano.
An unwavering glow of the tube is obtained by the Arduino Nano switching the IN-9 tube on and off at about 75 Hz. To prevent cathode poisoning of the IN-9 tube, a pleasant sweep animation is displayed at an adjustable interval.
The temperature sensor is a type DS18B20. As the total power consumption is under 1 watt, the thermometer may even be powered from a standard USB port on a computer.
The corresponding Elektor-Labs project page provides insights into the choice of the IN-9 tube and the way it is driven. A full kit of this project is available in Elektor's online Store. It is easy to assemble since only through-hole parts are used.
The complementing article with all the tech ins and outs of the project will appear in Elektor Magazine edition 4/2018 (July & August) due out by mid-June.